Subcategory Distribution
Recent News in General Relativity and Quantum Cosmology (gr-qc)
On the Holographic Dual of a Symmetry Operator at Finite Temperature
Topological symmetry operators of holographic large $N$ CFT$_D$'s are dual to dynamical branes in the gravity dual AdS$_{D+1}$. We use this correspondence to establish a dictionary between thermal expectation values of symmetry operators in the Euclidean CFT$_D$ and the evaluation of gravitational saddles in the presence of a dynamical brane. Expectation values of $0$-form symmetry operators in the CFT$_D$ are then related to branes wrapped on volume minimizing cycles in the bulk, i.e., the Euclidean continuation of a black hole horizon. We illustrate with some representative examples, including gravity in AdS$_3$, duality / triality defects in 4D $\mathcal{N} = 4$ Super Yang-Mills theory, and the dual of R-symmetry operators probing 5D BPS black holes.
Apparent $w<-1$ and a Lower $S_8$ from Dark Axion and Dark Baryons Interactions
We show that a simple coupling between dark energy and dark matter can simultaneously address two distinct hints at new physics coming from cosmological observations. The first is the recent evidence from the DESI project and supernovae observations that the dark energy equation of state~$w$ is evolving over cosmic time from an earlier value that is~$<-1$ to a present-day value~$>-1$. The second observation is the so-called~$S_8$ tension, describing the suppression of the growth of matter overdensities compared to that expected in the~$\Lambda$CDM model. We propose a stable, technically natural particle physics implementation of this idea, in which dark matter consists of dark baryons in a strongly-coupled hidden sector, and the dark energy field is the associated dark axion. The time-variation of the dark matter mass results in an effective dark energy equation of state that exhibits a phantom crossing behavior consistent with recent results. It also results in a slight delay in matter-radiation equality, which suppresses the overall growth of density perturbations.
Primodial power spectrum in loop quantum cosmology for different regularizations
In Loop Quantum Cosmology, the quantization of the Hamiltonian constraint involves a regularization procedure which is affected by certain ambiguities. Moreover, different regularizations lead to distinct mathematical formulations and, consequently, to different physical predictions. In this work, we explore the impact of this regularization on the primordial power spectrum of cosmological perturbations. More specifically, we study this power spectrum for the conventional regularization used in Loop Quantum Cosmology and for two alternative prescriptions suggested in the literature. We set initial conditions for the perturbations at the bounce corresponding to a recently proposed vacuum state, optimally adapted to the background dynamics. This choice of vacuum is based on an asymptotic Hamiltonian diagonalization in the ultraviolet sector of the perturbations which provides a non-oscillating power spectrum. Employing a suitable approximation to the propagation equations of the perturbations around the bounce, we are able to obtain an analytic expression for the primordial power spectrum of this vacuum for all the discussed regularizations. We compare the results and prove that the main relevant distinction between the corresponding spectra is the scale where power suppression occurs. The associated wavenumber scale is proportional to the square root of the critical density in Loop Quantum Cosmology, density which is different for each of the studied regularizations.
Natural inflation in Palatini $F(R,X)$
In the context of Palatini gravity, $F(R,X)$ models, with X the inflaton kinetic term, are characterized by the appealing property of generating asymptotically flat inflaton potentials. In this paper, we study the case of a Jordan frame potential which is positive and bounded, specifically, natural inflation. We compute the CMB observables and show that for a wide class of $F(R,X)$ theories, including the quadratic one, natural inflation is still viable.
Proto-neutron star oscillations including accretion flows
The gravitational wave signature from core-collapse supernovae (CCSNe) is dominated by quadrupolar oscillation modes of the newly born proto-neutron star (PNS), and could be detectable at galactic distances. We have developed a framework for computing the normal oscillation modes of a PNS in general relativity, including, for the first time, the presence of an accretion flow and a surrounding stalled accretion shock. These new ingredients are key to understand PNS oscillation modes, in particular those related to the standing-accretion-shock instability (SASI). Their incorporation is an important step towards accurate PNS asteroseismology. For this purpose, we perform linear and adiabatic perturbations of a spherically symmetric background, in the relativistic Cowling approximation, and cast the resulting equations as an eigenvalue problem. We discretize the eigenvalue problem using collocation Chebyshev spectral methods, which is then solved by means of standard and efficient linear algebra methods. We impose boundary conditions at the accretion shock compatible with the Rankine-Hugoniot conditions. We present several numerical examples to assess the accuracy and convergence of the numerical code, as well as to understand the effect of an accretion flow on the oscillation modes, as a stepping stone towards a complete analysis of the CCSNe case.
The First Model-Independent Chromatic Microlensing Search: No Evidence in the Gravitational Wave Catalog of LIGO-Virgo-KAGRA
The lensing of Gravitational Waves (GWs) due to intervening matter distribution in the universe can lead to chromatic and achromatic signatures in the wave-optics and geometrical-optics limit respectively. This makes it difficult to model for the unknown mass distribution of the lens and hence requires a model-independent lensing detection technique from GW data. We perform the first model-independent microlensing search in the wave-optics limit on the 80 GW events observed with both the LIGO detectors from the third observation catalog GWTC-3 of LIGO-Virgo-KAGRA using the analysis method $\mu$-\texttt{GLANCE}. These unmodelled searches pick up one plausible candidate $\rm GW190408\_181802$ with a slightly above threshold residual amplitude compared to the residual expected from detector noise. However, exploring the microlensing modulation signatures on this event, we do not find any conclusive evidence of the microlensing signal in the data. With this, we confidently rule out the presence of any statistically significant microlensing signal in the 80 events of GWTC-3 in a model-independent way.
Thermodynamics of sign-switching dark energy models
We perform a comprehensive thermodynamic analysis of three sign-switching dark energy models in a flat FLRW cosmology: graduated dark energy (gDE), sign-switching cosmological constant ($\Lambda_s$), and smoothed sign-switching cosmological constant ($\Lambda_t$). We systematically derive key cosmological thermodynamic quantities -- horizon temperature, horizon entropy, internal entropy, total entropy, and their first and second derivatives -- using the Generalised Second Law (GSL) as the fundamental evaluation criterion. We first confirm the compliance of the $\Lambda$CDM model with the GSL, establishing a baseline for comparison. We find that despite their unconventional negative-to-positive energy density transitions, both $\Lambda_s$ and $\Lambda_t$ remain thermodynamically consistent. In contrast, gDE exhibits significant issues: divergences in its equation-of-state lead to infinite horizon temperature and entropy derivatives; and asymptotically, the horizon temperature diverges while entropy approaches zero, causing entropy reduction and violating the GSL. We highlight a key insight: models with divergences in the product of the dark energy equation-of-state parameter and its energy density ($w_x \Omega_x$) inevitably produce thermodynamic inconsistencies in standard cosmology. This thermodynamic approach provides a complementary criterion alongside observational constraints for evaluating the physical viability of cosmological models.
Spherically symmetric horizonless solutions and their frozen states in Bardeen spacetime with Proca field
In this paper, we construct a static spherical symmetric Bardeen-Proca star (BPS) model, which consists of the electromagnetic field and Proca field minimally coupled with gravity. The introduction of the Proca field disrupts the formation of event horizons, ensuring that these solutions are globally regular throughout the spacetime. We obtain families of BPS solutions under several magnetic charge conditions. Based on these results, we further investigate the ADM mass, Noether charge, and energy density distribution of them. We find that when the magnetic charge is sufficiently large, solutions with a critical horizon $r_{cH}$ emerge as $\omega \rightarrow 0$, and the time component of the metric approaches zero inside $r_{cH}$. To an observer at infinity, the collapse process of the matter near the critical horizon appears frozen. Consequently, we refer to the solution with $r_{cH}$ as the frozen Bardeen-Proca star (FBPS). Additionally, we also investigate the circular geodesic orbits of BPS. For the light ring, we find that the light rings always appear in pairs, located on both sides of the critical horizon and moving further apart as the frequency $\omega$ decreases. For timelike circular orbits, we investigate their distribution in the spacetime of BPSs and highlight four representative families of BPS solutions.
Superluminal Dark Photons as a Solution to the GRB 221009A Anomaly
The detection of exceptionally high-energy {\gamma}-photons (up to 18 TeV) from GRB 221009A by the LHAASO Collaboration challenges conventional physics. Photon-axion-like particle (ALP) oscillations have been proposed to explain this anomaly, but they rely on specific parameter tuning. We present an alternative explanation involving superluminal dark photons. Building on the frameworks of Markoulakis and Valamontes, we propose that dark photons facilitated faster-than-light (FTL) propagation of information, allowing {\gamma}-photons to bypass extragalactic background light (EBL) attenuation. This hypothesis aligns with cosmological observations and experimental results, including those from the LHC, providing a robust framework for addressing the GRB 221009A anomaly.
Stability of Positive Mass Theorem for Static Quasi-Local Energy of Compact (Locally) Hyperbolic Graphical Manifolds
In this paper, we consider compact graphical manifolds with boundary over (locally) hyperbolic static space. We prove the stability of the positive mass theorem with respect to the Federer--Fleming flat distance for the static quasi-local Brown-York energy of the outer boundary of compact (locally) hyperbolic graphical manifolds.
Probing classical and quantum violations of the equivalence of active and passive gravitational mass
The equivalence of active and passive (EAP) gravitational mass is one of the most fundamental principles of gravity. But in contrast to the usual equivalence of inertial and (passive) gravitational mass, the EAP has not received much attention. Here we revisit this principle and show how it can be used to probe quantum gravity in laboratory-based experiments. We first examine how the dynamics under EAP violations affects classical systems and show that new laboratory tests can be performed, to improve over the current experimental bounds and to test new manifestations of EAP violations. We then extend the analysis to the quantum domain, where quantized energy contributes to mass and the EAP principle can thus shed light on how quantum source masses would gravitate. We show that experiments with cold polar molecules, and future experiments with nuclear atomic clocks, can test the quantum EAP in a regime where quantum gravity phenomenology could become relevant. Our results open new opportunities for fundamental tests of gravity in high-precision laboratory experiments that can shed light on foundational principles of gravity and its interface with quantum theory.
The entropy of dynamical de Sitter horizons
We propose a new formula for the entropy of a dynamical cosmological event horizon, which is valid to leading order for perturbations of a stationary asymptotically de Sitter spacetime. By introducing a nontrivial correction term, we generalize Gibbons and Hawking's first law of event horizons to non-stationary eras. We also develop the non-stationary physical process first law between two arbitrary horizon cross-sections for the cosmological event horizon.
Testing f (R) gravity models with DESI-BAO and other cosmological data
In this paper, we conduct a statistical analysis of various cosmological models within the framework of f (R) gravity theories, motivated by persistent challenges in modern cosmology, such as the unknown mechanisms driving the late-time accelerated expansion of the universe. We begin by presenting a comprehensive formulation of these theories and discussing their potential to resolve the outstanding issues. Following this, we perform a detailed statistical examination in a cosmological context, leveraging a wide array of observational data. Special attention is given to the incorporation of the latest Baryon Acoustic Oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI) and of the Pantheon++SH0ES compilation, which play a critical role in constraining these models. Our results show an increase in the values of the distortion parameter b and of the Hubble parameter H0 estimates, due to the use of this new compilation of SnIa data. However, no major changes are perceived when using the DESI data set instead of the previous BAO observations.
Long-lived Quasinormal Modes and Gray-Body Factors of black holes and wormholes in dark matter inspired Weyl Gravity
We calculate quasinormal modes and gray-body factors of a massive scalar field in the background of three compact objects in the Weyl gravity: Schwarzschild-like black holes, known as Mannheim-Kazanas solution, non-Schwrazschild-like black holes and traversable wormholes found recently in [P. Jizba, K. Mudru\v{n}ka, Phys.Rev.D 110 (2024) 12, 124006]. We show that the spectrum of the massive field is qualitatively different from massless one both in the frequency and time domains. While the mass term leads to much longer lifetime of the modes, the arbitrarily long-lived modes, known as quasi-resonances, are not achieved.
The transition to phenomenological behaviour of static solutions of the Einstein-Dirac system for an increasing number of fermions
Static spherically symmetric solutions to the Einstein-Dirac system were constructed numerically for the first time in 1999 by Finster, Smoller and Yau \cite{FSY1} in the case of two fermions. In 2020 this result was generalized by Leith, Hooley, Horne and Dritschel \cite{LHHD} to a system consisting of an even number $\kappa$ of fermions. They constructed solutions for $2\leq\kappa\leq 90$. The purpose of the present investigation is to compare the properties of static solutions of the Einstein-Dirac system with static solutions of the Einstein,-Vlasov system as the number of fermions increases, that is, for $2\leq\kappa \leq 180$. Since the Einstein-Vlasov system is a fully classical physical model, whereas the Einstein-Dirac system is semiclassical and thus has a quantum signature, this framework provides an excellent opportunity to study the transition from quantum to classical behaviour. It turns out that even for a comparatively small number of particles, the features of the solutions are remarkably similar. For both systems, we find highly relativistic solutions having a multi-peak structure with strikingly similar characteristics. We also investigate the maximum compactness ratio $\sup 2m/r$ of the solutions. The solutions of both systems share the fundamental properties regarding the maximum compactness ratio and obey the inequality derived in \cite{A2}. Furthermore, we investigate the sign of the pressure components of solutions of the Einstein-Dirac system. For small values of $\kappa$, there are regions where the radial pressure is negative. These regions disappear as $\kappa$ increases. This supports the interpretation we make as a transition from quantum to classical behaviour as the number of fermions increases.
Small-scale metric structure and horizons: Probing the nature of gravity
A recently developed tool allows for a description of spacetime as a manifold with a Lorentz-invariant (lower) limit length built-in. This is accomplished in terms of geometric quantities depending on two spacetime events (bitensors) and looking at the 2-point function of fields on it, all this being well suited to embody nonlocality at the small scale. What one gets is a metric bitensor with components singular in the coincidence limit of the two events, capable to provide a finite distance in the same limit. We discuss here how this metric structure encompasses also the case of null separated events, and describe some results one obtains with the null qmetric which do have immediate thermodynamic/statistical interpretation for horizons. One of them is that the area transverse to null geodesics converging to a base point goes to a finite value in the coincidence limit (instead of shrinking to 0). We comment on the discreteness this seems to imply for the area of black hole horizons as well as on possible ensuing effects in gravitational waves from binary black hole coalescences.
Copenhagen Survey on Black Holes and Fundamental Physics
The purpose of this survey is to take a snapshot of the attitudes of physicists, which may be useful to sociologists and historians of science. A total of 85 completed surveys were returned out of 151 registered participants of the "Black holes Inside and out" conference, held in Copenhagen in 2024. The survey asked questions about the nature of black holes and some of the most contentious issues in fundamental physics. A number of surprising results were found. For example, some of the leading frameworks, such the cosmological constant, cosmic inflation, or string theory, while most popular, gain less than majority of votes from the participants. The only statement that gains majority approval (by 68% of participants) was that the Big Bang means that "the universe evolved from a hot dense state", not "an absolute beginning time". This provides reasons for caution in describing ideas as consensus in the scientific community when a more nuanced view may be justified.
Search for continuous gravitational waves from neutron stars in five globular clusters with a phase-tracking hidden Markov model in the third LIGO observing run
A search is performed for continuous gravitational waves emitted by unknown neutron stars in five nearby globular clusters using data from the third Laser Interferometer Gravitational-Wave Observatory (LIGO) observing run, over the frequency range $100$--$800\,\mathrm{Hz}$. The search uses a hidden Markov model to track both the frequency and phase of the continuous wave signal from one coherent segment to the next. It represents the first time that a phase-tracking hidden Markov model has been used in a LIGO search. After applying vetoes to reject candidates consistent with non-Gaussian artifacts, no significant candidates are detected. Estimates of the strain sensitivity at 95\% confidence $h_{0,\mathrm{eff}}^{95\%}$ and corresponding neutron star ellipticity $\epsilon^{95\%}$ are presented. The best strain sensitivity, $h_{0,\mathrm{eff}}^{95\%} = 2.7 \times 10^{-26}$ at $211\,\mathrm{Hz}$, is achieved for the cluster NGC6544.
Ignition of weak interactions and r-process outflows in super-collapsar accretion disks
The collapse of rotating massive (~$10 M_\odot$) stars resulting in hyperaccreting black holes (BHs; "collapsars") is a leading model for the central engines of long-duration gamma-ray bursts (GRBs) and a promising source of rapid neutron capture ("r-process") elements. R-process nucleosynthesis in disk outflows requires the accretion flow to self-neutronize. This occurs because of Pauli-blocking at finite electron degeneracy, associated with a critical accretion rate $\dot M > \dot{M}_{\rm ign}$. We analytically examine the assumptions underlying this "ignition threshold" and its possible breakdown with increasing BH mass $M$. Employing three-dimensional general-relativistic magnetohydrodynamic simulations with weak interactions, we explore the physical conditions of collapsar accretion disks with $M$ ~ 80-3000 $M_\odot$ over more than a viscous timescale as they transition through the threshold. There is remarkable agreement between our simulations and the analytic result $\dot{M}_{\rm ign}\propto \alpha^{5/3}M^{4/3}$ for $M$ ~ 3-3000 $M_\odot$. Simulations and analytic analyses consistently show that the largest BHs leading to r-process nucleosynthesis at $\dot{M}_{\rm ign}$ are $\approx 3000 M_\odot$, beyond which self-neutronization ceases, since the disk temperature $T\propto M^{-1/6}$ decreases below the neutron-proton mass difference (~MeV), suppressing the conversion of protons into neutrons. We show that stellar models of ~$250-10^5M_\odot$ can give rise to BHs of $M$ ~30-1000 $M_\odot$ accreting at $\dot M\gtrsim \dot{M}_{\rm ign}$, yielding ~$10-100 M_\odot$ of light and heavy r-process elements per event. These rare but prolific r-process sources in low-metallicity environments are associated with super-kilonovae and likely extremely energetic GRBs. Such signatures may be used to probe Population III stars.
A low-redshift preference for an interacting dark energy model
We explore an interacting dark sector model in trace-free Einstein gravity where dark energy has a constant equation of state, $w=-1$, and the energy-momentum transfer potential is proportional to the cold dark matter density. Compared to the standard $\Lambda$CDM model, this scenario introduces a single additional dimensionless parameter, $\epsilon$, which determines the amplitude of the transfer potential. Using a combination of \textit{Planck} 2018 Cosmic Microwave Background (CMB), DESI 2024 Baryon Acoustic Oscillation (BAO), and Pantheon+ Type Ia supernovae (SNIa) data, we derive stringent constraints on the interaction, finding $\epsilon$ to be of the order of $\sim \mathcal{O}(10^{-4})$. While CMB and SNIa data alone do not favor the presence of such an interaction, the inclusion of DESI data introduces a mild $1\sigma$ preference for an energy-momentum transfer from dark matter to dark energy. This preference is primarily driven by low-redshift DESI BAO measurements, which favor a slightly lower total matter density $\Omega_m$ compared to CMB constraints. Although the interaction remains weak and does not significantly alleviate the $H_0$ and $S_8$ tensions, our results highlight the potential role of dark sector interactions in late-time cosmology.
Prompt Periodicity in the GRB 211211A Precursor: Black-hole or magnetar engine?
The merger origin long GRB 211211A was a class (re-)defining event. A precursor was identified with a $\sim 1$ s separation from the main burst, as well as a claimed candidate quasi-periodic oscillation (QPO) with a frequency $\sim20$ Hz. Here, we explore the implications of the precursor, assuming the quasi-periodicity is real. The precursor variability timescale requires relativistic motion with a Lorentz factor $\Gamma\gtrsim80$, and implies an engine driven jetted outflow. The declining amplitude of the consecutive pulses requires an episodic engine with an `on/off' cycle consistent with the QPO. For a black-hole central engine, the QPO can have its origin in Lense-Thirring precession of the inner disk at $\sim6-9$ $r_g$ (gravitational radii) for a mass $M_\bullet\leq4.5$ M$_{\odot}$, and $\lesssim 7$ $r_g$ for $M_\bullet>4.5$ M$_{\odot}$ and dimensionless spin $\chi\sim 0.3 - 0.9$. Alternatively, at a disk density of $\sim10^{8 - 12}$ g cm$^{-3}$, the required magnetic field strength for a QPO via magnetohydrodynamic effects will be on the order $B\sim10^{12 - 14}$ G. If the central engine is a short lived magnetar or hypermassive neutron star, then a low-frequency QPO can be produced via instabilities within the disk at a radius of $\sim20 - 70$ km, for a disk density $\sim10^{9 - 12}$ g cm$^{-3}$ and magnetic field $\gtrsim10^{13 - 14}$ G. The QPO cannot be coupled to the neutron star spin, as the co-rotation radius is beyond the scale of the disk. Neither engine can be ruled out -- however, we favour an origin for the precursor candidate QPO as early jet-disk coupling for a neutron star -- black hole merger remnant with mass $M_\bullet>4.5$ M$_{\odot}$.
Perturbations of spinning black holes in dynamical Chern-Simons gravity: Slow rotation quasinormal modes
Gravitational waves offer new ways to test general relativity (GR) in the strong-field regime, including tests involving the ringdown phase of binary black hole mergers, characterized by oscillating and quickly decaying quasinormal modes (QNMs). Recent advances have extended QNM calculations to several theories beyond GR through the development of the modified Teukolsky formalism, including higher derivative gravity and dynamical Chern-Simons (dCS) gravity. Using the modified Teukolsky formalism, we previously derived radial second-order differential equations governing curvature and scalar field perturbations in dCS gravity at leading order in spin. In this work, we compute the QNM frequency shifts for slowly rotating black holes in dCS gravity from these modified Teukolsky equations, and (1) show that the radial equations for Weyl scalars $\Psi_{0,4}$ can be separated into even- and odd-parity parts, confirming that the scalar field couples only to the odd-parity sector; (2) extend the eigenvalue perturbation method to coupled fields; (3) compute the QNM spectrum, obtaining consistent results across independent calculations using different radiation gauges; (4) calculate the overtones in the QNM spectra for the first time in dCS gravity; (5) show that our findings align with previous metric perturbation studies and mark the first QNM spectrum calculation in a non-minimally coupled scalar-tensor theory via the modified Teukolsky formalism. This work lays the foundation for studying fast-rotating black holes in dCS gravity, advancing black hole spectroscopy in beyond-GR contexts.
Limits on the Ejecta Mass During the Search for Kilonovae Associated with Neutron Star-Black Hole Mergers: A case study of S230518h, GW230529, S230627c and the Low-Significance Candidate S240422ed
Neutron star-black hole (NSBH) mergers, detectable via their gravitational-wave (GW) emission, are expected to produce kilonovae (KNe). Four NSBH candidates have been identified and followed-up by more than fifty instruments since the start of the fourth GW Observing Run (O4), in May 2023, up to July 2024; however, no confirmed associated KN has been detected. This study evaluates ejecta properties from multi-messenger observations to understand the absence of detectable KN: we use GW public information and joint observations taken from 05.2023 to 07.2024 (LVK, ATLAS, DECam, GECKO, GOTO, GRANDMA, SAGUARO, TESS, WINTER, ZTF). First, our analysis on follow-up observation strategies shows that, on average, more than 50% of the simulated KNe associated with NSBH mergers reach their peak luminosity around one day after merger in the $g,r,i$- bands, which is not necessarily covered for each NSBH GW candidate. We also analyze the trade-off between observation efficiency and the intrinsic properties of the KN emission, to understand the impact on how these constraints affect our ability to detect the KN, and underlying ejecta properties for each GW candidate. In particular, we can only confirm the kilonova was not missed for 1% of the GW230529 and S230627c sky localization region, given the large sky localization error of GW230529 and the large distance for S230627c and, their respective KN faint luminosities. More constraining, for S230518h, we infer the dynamical ejecta and post-merger disk wind ejecta $m_{dyn}, m_{wind}$ $<$ $0.03$ $M_\odot$ and the viewing angle $\theta>25^\circ$. Similarly, the non-astrophysical origin of S240422ed is likely further confirmed by the fact that we would have detected even a faint KN at the time and presumed distance of the S240422ed event candidate, within a minimum 45% credible region of the sky area, that can be larger depending on the KN scenario.
Orbital eccentricity in a neutron star - black hole binary
The observation of gravitational waves from merging black holes and neutron stars provides a unique opportunity to discern information about their astrophysical environment. Two signatures that are considered powerful tracers to distinguish between different binary formation channels are general-relativistic spin-induced orbital precession and orbital eccentricity. Both effects leave characteristic imprints in the gravitational-wave signal that can be extracted from observations. To date, neither precession nor eccentricity have been discerned in neutron star - black hole binaries. Here we report the first measurement of orbital eccentricity in a neutron star - black hole binary. Using, for the first time, a waveform model that incorporates precession and eccentricity, we perform Bayesian inference on the event GW200105 and infer a median orbital eccentricity of $e_{20}\sim 0.145$ at an orbital period of $0.1$s, excluding zero at more than $99\%$ confidence. We find inconclusive evidence for the presence of precession, consistent with previous, non-eccentric results. Our result implies a fraction of these binaries will exhibit orbital eccentricity even at small separations, suggesting formation through mechanisms involving dynamical interactions beyond isolated binary evolution. Future observations will reveal the contribution of eccentric neutron star - black hole binaries to the total merger rate across cosmic time.
Quantum Creation of a FRW Universe: applying the Riesz fractional derivative
In this work, we apply fractional calculus to study quantum cosmology. Specifically, our Wheeler-DeWitt equation includes a FRW geometry, a radiation fluid, a positive cosmological constant, and an ad hoc potential; we employ the Riesz fractional derivative, which brings a parameter $\alpha$, where $1 < \alpha \leq 2$, appearing explicitly in the mentioned equation. We investigate numerically the tunnelling probability for the Universe to emerge using a suitable WKB approximation. Our findings are as follows. When we decrease the value for $\alpha$, the tunnelling probability also decreases, suggesting that if fractional features could be considered to ascertain among different early universe scenarios, then the value $\alpha=2$ (meaning strict locality and standard cosmology) would be the most likely. Finally, our results also allow for an interesting discussion between selecting values for $\Lambda$ (in a non-fractional conventional set-up) versus balancing, e.g., both $\Lambda$ and $\alpha$ in the fractional framework. Concretely, the probability transition in the former if, e.g., $\Lambda=0.7$, is very close to the value computed if in the latter we employ instead, e.g., $\Lambda=1.5$ and $\alpha=1.9397961$.
QNMs of charged black holes in AdS spacetime: a geometrical optics perspective
We investigate the quasinormal modes of the Reissner$-$Nordstr\"om anti$-$de Sitter black hole using the Penrose limit, motivated by the geometrical optics approximation. This approach offers a novel framework for approximating quasinormal modes with large real frequencies by associating a plane wave to spacetime regions near null geodesics, providing a geometric interpretation of the geometrical optics approximation. Applying this limit to bound null orbits around black holes allows us to explore the black hole response to perturbations. We analyze the effects of black hole charge and negative cosmological constant on the quasinormal spectrum, finding that increasing charge enhances both the real and imaginary parts of the frequencies, while a decreasing cosmological constant leads to higher real frequencies and longer lived perturbations, with the spectrum stabilizing at larger values of the cosmological constant.
Rotating scalarized black holes: the role of the coupling
We perform an in-depth analysis of rotating scalarized black holes in scalar-Gauss-Bonnet gravity, where scalarization is induced by the spacetime curvature. Our results show that even for very large spins, the scalar charge can reach values comparable to those in the static limit, meaning it is not significantly suppressed. Consequently, curvature-induced scalarization can lead to non-GR signatures of similar magnitude in both static and rapidly rotating cases. For certain coupling parameters, these scalarized black hole solutions remain within the regime of validity of the effective field theory, where the theory has well-posed formulations.
Photon Absorption in a Doubly Special Relativity Model with Undeformed Free Propagation and Total Momentum Conservation
The lack of a dynamical framework within doubly special relativity theories has impeded the development of a corresponding phenomenology of modified interactions. In this work we show that in a model based on the classical basis of $\kappa$-Poincar\'e and total momentum conservation, one has a well-defined cross section of the photon-photon annihilation process, once a prescription for the channel treatment is set. The modification of the interaction can lead to observable effects in the opacity of the Universe to very high-energy gamma rays when the gamma-ray energy approaches the energy scale of the deformation. The magnitude and observability of this deformation are examined as functions of the gamma-ray energy and source distance.
Primordial correlators from multi-point propagators
A key step in the comparison between inflationary predictions and cosmological observations is the computation of primordial correlators. Numerical methods have been developed that overcome some of the difficulties arising in analytical calculations when the models considered are complex. The PyTransport package, which implements the transport formalism, allows computation of the tree-level 2- and 3-point correlation functions for multi-field models with arbitrary potentials and a curved field space. In this work we investigate an alternative numerical implementation of the transport approach, based on the use of transfer ''matrices'' called multi-point propagators (MPP). We test the novel MPP method, and extensively compare it with the traditional implementation of the transport approach provided in PyTransport. We highlight advantages of the former, discussing its performance in terms of accuracy, precision and running time, as well as dependence on the number of e-folds of sub-horizon evolution and tolerance settings. For topical ultra-slow-roll models of inflation we show that MPPs (i) precisely track the decay of correlators even when PyTransport produces erroneous results, (ii) extend the computation of squeezed bispectra for squeezing values at least one decade beyond those attainable with PyTransport.
Noncommutative Quasinormal Modes and the Violation of Isospectrality
We explore quasinormal modes (QNMs) of the Schwarzschild black hole under a noncommutative (NC) deformation of spacetime, constructed via a Drinfeld twist formalism. In this approach, the usual Regge--Wheeler (axial) and Zerilli (polar) equations acquire additional contributions that depend on the NC parameter. Employing semi-analytical approximations (high-order WKB, P\"oschl--Teller and Rosen--Morse), we calculate the corresponding QNM spectra. Our results show that whereas the commutative case preserves the isospectrality of axial and polar modes, noncommutativity systematically violates this degeneracy. The discrepancy grows with the strength of the NC parameter, becoming evident through distinct real and imaginary parts in the ringdown frequencies. These findings highlight the potential of black hole QNMs to serve as probes of quantum-spacetime corrections in strong-field regimes.
Covariant effective spacetimes of spherically symmetric electro-vacuum with a cosmological constant
An algebraic framework was introduced in our previous works to address the covariance issue in spherically symmetric effective quantum gravity. This paper extends the framework to the electro-vacuum case with a cosmological constant. After analyzing the notion of covariance in the classical theory, we propose an effective Hamiltonian for the electromagnetic field. The effective Hamiltonian together with the effective Hamiltonian constraint of gravity determines an effective dynamical model of gravity coupled to electromagnetic. The resulting model is covariant with respect to both the effective metric and the effective vector potential. By solving the equations of motion derived from the effective Hamiltonian constraint, we obtain several quantum-corrected solutions. Notably, some of these solutions reveal quantum gravity effects manifesting not only in spacetime metrics but also in the electromagnetic field. Finally, the covariance of coupling models with general matter fields is discussed.
Gregory-Laflamme-type instability of boson strings and related phases in D=5 Kaluza-Klein theory
We add an $S^1$ extra dimension (size $L$) to the well known $D=4$ static, spherically symmetric $Q$-balls and boson stars. We show that the resulting uniform horizonless boson strings possess a static zero-mode for a critical value of $L$. This is at the threshold of a Gregory-Laflamme instability of these objects, occurring for larger values of $L$.The non-linear continuation of the zero-mode yields $D=5$ non-uniform boson strings. In addition, there are also intrinsic $D=5$ solutions describing localized boson stars on the $S^1$, supported by the contribution of the scalar field Kaluza-Klein modes. Basic properties of all three types of aforementioned solutions are discussed, together with their phase space.
Orbits of photon in Bardeen-boson stars and their frozen states
In a recent study [1], the Bardeen-boson star (BBS) model involving a scalar field minimally coupled to Einstein gravity and a Bardeen's nonlinear electromagnetic field was investigated. It was found that when the magnetic charge $q$ of the electromagnetic field exceeds a certain critical value $q_c$, a frozen Bardeen-boson star (FBBS) can be obtained with the frequency approaching zero. In this paper, we study the null orbits in the background of the general BBS and FBBS. We find that similar to the boson star (BS), all BBSs do not have the event horizon and possess complete null geodesics, allowing photons to move throughout the entire spacetime of BBS. Among these BBSs, the FBBSs whose spacetime is very similar to that of black holes are particularly special. The null orbits around the FBBSs exhibit sharp deflections near the critical horizon while becoming nearly straight inside the critical horizon. Furthermore, the photon in the background of FBBSs moves for a very long time inside the critical horizon from the perspective of an infinity viewer.
Constraining Axially Symmetric Bianchi Type I Model with Self-Consistent Recombination History and Observables
Recent cosmological measurements suggest the possibility of an anisotropic universe. As a result, the Bianchi Type I model, being the simplest anisotropic extension to the standard Friedmann-Lema\^itre-Robertson-Walker metric has been extensively studied. In this work, we show how the recombination history should be modified in an anisotropic universe and derive observables by considering the null geodesic. We then constrain the axially symmetric Bianchi Type I model by performing Markov Chain Monte Carlo with the acoustic scales in Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillation data, together with local measurements of $H(z)$ and Pantheon Supernova data. Our results reveal that the anisotropic model is not worth a bare mention compared to the $\Lambda$CDM model, and we obtain a tight constraint on the anisotropy that generally agrees with previous studies under a maximum temperature anisotropy fraction of $2\times 10^{-5}$. To allow for a non-kinematic CMB dipole, we also present constraints based on a relaxed maximum temperature anisotropy comparable to that of the CMB dipole. We stress that there is a significant difference between the geodesic-based observables and the naive isotropic analogies when there is a noticeable anisotropy. However, the changes in recombination history are insignificant even under the relaxed anisotropy limit.
Axion Stabilization in Modular Cosmology
The $SL(2,\mathbb{Z})$ invariant $\alpha$-attractor models have plateau potentials with respect to the inflaton and axion fields. The potential in the axion direction is almost exactly flat during inflation, hence, the axion field remains nearly massless. In this paper, we develop a generalized class of such models, where the $SL(2,\mathbb{Z})$ symmetry is preserved, but the axion acquires a large mass and becomes strongly stabilized during inflation, which eliminates isocurvature perturbations in this scenario. Inflation in such two-field models occurs as in the single-field $\alpha$-attractors and leads to the same cosmological predictions.
Inferring astrophysics and cosmology with individual compact binary coalescences and their gravitational-wave stochastic background
Gravitational waves (GWs) from compact binary coalescences (CBCs) provide a new avenue to probe the cosmic expansion, in particular the Hubble constant $H_0$. The spectral sirens method is one of the most used techniques for GW cosmology. It consists of obtaining cosmological information from the GW luminosity distance, directly inferred from data, and the redshift that can be implicitly obtained from the source frame mass distribution of the CBC population. With GW detectors, populations of CBCs can be either observed as resolved individual sources or implicitly as a stochastic gravitational-wave background (SGWB) from the unresolved ones. In this manuscript, we study how resolved and unresolved sources of CBCs can be employed in the spectral siren framework to constrain cosmic expansion. The idea stems from the fact that the SGWB can constrain additional population properties of the CBCs thus potentially improving the measurement precision of the cosmic expansion parameters. We show that with a 5-detector network at O5-designed sensitivity, the inclusion of the SGWB will improve our ability to exclude low values of $H_0$ and the dark matter energy fraction $\Omega_m$, while also improving the determination of a possible CBC peak in redshift. Although low values of $H_0$ and $\Omega_m$ will be better constrained, we obtain that most on the precsion on $H_0$ will be provided by resolved spectral sirens. We also performed a spectral siren analysis for 59 resolved binary black hole sources detected during the third observing run with an inverse false alarm rate higher than 1 per year jointly with the SGWB. We obtain that with current sensitivities, the cosmological and population results are not impacted by the inclusion of the SGWB.
Higgs mode of modified cosmology
We consider a model where the Standard Model is added to the Einstein Lagrangian together with a Jordan-Brans-Dicke(JBD) coupling. The time-dependent Higgs field has an important role in interpreting the effective gravitational constant, $G_{eff}$. This may lead to two Big Bangs, the first Big Bang characterizes the size of the universe being zero. At this Big Bang, the value of the effective gravitational constant is zero and starts decreasing in time through negative values. During this era, the JBD term is important. In the second Big Bang, the effective gravitational constant passes through infinity to positive values. The negative gravitational constant is interpreted as repulsive gravity. The Lagrangian density provides effective potentials leading to spontaneous symmetry breaking which gives cosmological expectation value of the Higgs field and the Higgs mass which depends on curvature and the Brans Dicke parameter.
The wavefunction of a quantum $S^1 \times S^2$ universe
We study quantum gravity corrections to the no-boundary wavefunction describing a universe with spatial topology $S^1\times S^2$. It has been suggested that quantum effects become increasingly important when the size of the circle is large relative to the sphere. In this paper, we confirm this claim by an explicit four-dimensional one-loop calculation of the gravitational path integral preparing such a state. In the process, we clarify some aspects of the gravitational path integral on complex spacetimes. These quantum corrections play a crucial role in ensuring that the norm of the wavefunction is naturally expressed in terms of a path integral over $S^2 \times S^2$ at the classical level. We extend some of the analysis to more general spatial topologies, as well as to the inclusion of fermions.
Tidal dissipation in binary neutron star inspiral : Bias study and modeling of frequency domain phase
During the inspiral of a binary neutron star, viscous processes in the neutron star matter can damp out the tidal energy induced by its companion and convert it to thermal energy. This tidal dissipation/heating process introduces a net phase shift in the gravitational wave signal. In our recent work (Ghosh et al., Phys. Rev. D 109, 103036 (2024)), we showed that tidal dissipation from bulk viscosity originating from the non-leptonic weak interactions involving hyperons could have a detectable phase shift in the gravitational-wave (GW) signal in the next-generation GW detectors. In this work, we model the dephasing due to tidal dissipation in a post-Newtonian (PN) expansion and incorporate this in gravitational waveforms for equal mass binary neutron stars. We then estimate the systematic bias incurred in tidal deformability measurements in simulated signal injection studies when this physical effect is not accounted for in waveform models. Lastly, we perform a full Bayesian parameter estimation with our model to show how accurately we can measure the additional phase due to tidal dissipation in future GW observations and discuss its significance in extreme matter studies.
Rotating Einstein-Maxwell-Dilaton Black Hole as a Particle Accelerator
Similar to particle accelerators, black holes also have the ability to accelerate particles, generating significant amounts of energy through particle collisions. In this study, we examine the horizon and spacetime structures of a rotating black hole within the framework of Einstein-Maxwell-Dilaton gravity. Additionally, we extend the analysis to explore particle collisions and energy extraction near this black hole using the Banados-Silk-West mechanism. Our findings reveal that the mass and angular momentum of the colliding particles significantly influence the center of mass energy, more so than the parameters of the black hole itself. Furthermore, we apply the Banados-Silk-West mechanism to massless particles, particularly photons, while disregarding their intrinsic spin in plasma; an aspect that has not been previously explored. The Banados-Silk-West mechanism cannot be directly applied, as the refractive index condition only permits photon propagation, meaning that massive particles in vacuum cannot be included in this study. We derive the propagation conditions for photons and analyze photon collisions by treating them as massive particles in a dispersive medium. The impact of the plasma parameter on the extracted center of mass energy is also examined. Our results show that the plasma parameter has a relatively weak and unchanged effect on the center of mass energy across all cases, indicating that energy losses due to friction within the medium are a contributing factor.
Superconductivity in Magnetars: Exploring Type-I and Type-II States in Toroidal Magnetic Fields
We present a first two-dimensional general-relativistic analysis of superconducting regions in axially symmetric highly magnetized neutron star (magnetar) models with toroidal magnetic fields. We investigate the topology and distribution of type-II and type-I superconducting regions for varying toroidal magnetic field strengths and stellar masses by solving the Einstein-Maxwell equations using the XNS code. Our results reveal that the outer cores of low- to intermediate-mass magnetars sustain superconductivity over larger regions compared to higher-mass stars with non-trivial distribution of type-II and type-I regions. Consistent with previous one-dimensional (1D) models, we find that regardless of the gravitational mass, the inner cores of magnetars with toroidal magnetic fields are devoid of $S$-wave proton superconductivity. Furthermore, these models contain non-superconducting, torus-shaped regions - a novel feature absent in previous 1D studies. Finally, we speculate on the potential indirect effects of superconductivity on continuous gravitational wave emissions from millisecond pulsars, such as PSR J1843-1113, highlighting their relevance for future gravitational wave detectors.
Four-dimensional Stationary Algebraically Special Solutions and Soft Hairs
We derive the Ricci-flat metrics in four dimensions that are stationary and algebraically special, together with the locally asymptotically flat conditions in the Bondi-Sachs framework. The solutions consist of a pair of arbitrary holomorphic and antiholomorphic functions analogous to the Virasoro modes, and also three constant parameters originated from the $Y_{1,m}$ modes in spherical harmonic expansion. We show that the higher modes of the (anti-)holomorphic function contain an infinite tower of soft hairs from the perspectives of both the local gravitational degree of freedom and the asymptotic supertranslation charges. Within our general ansatz, we obtain from the zero modes the complete set of algebraic Petrov type-D solutions of four free parameters. We show that one parameter does not belong to the Plebanski-Demianski class and, therefore, yields a new type-D metric.
Effective-one-body modeling for generic compact binaries with arbitrary orbits
We present the first unified model for the general relativistic dynamics and gravitational radiation of generic compact binaries. TEOBResumS-Dal\'i is a model based on the effective-one-body framework incorporating tidal interactions, generic spins, multipolar radiation reaction/waveform and numerical-relativity information. It allows the computation of gravitational waves and other dynamical gauge invariants from generic binaries (black holes, neutron stars, neutron star-black hole binaries) evolving along arbitrary orbits (quasi-circular, eccentric, non-planar) through merger and including scattering. The performances of TEOBResumS-Dal\'i in the strong-field regime are showcased by comparisons with a large sample of 1395 high-accuracy numerical-relativity simulations available. TEOBResumS-Dal\'i allows the computation of faithful waveforms for gravitational wave astronomy, providing at the same time an understanding and a prediction of the strong-field dynamics.
Impacts of Primordial Black Holes in the Early Universe
The work presented in this thesis draws back the curtain on the physics of the primordial universe by leveraging Primordial Black Holes (PBHs) as cosmological probes. The violent deaths of ultralight PBHs are shown to severely inhibit leptogenesis, alter the sphaleron freeze-out temperature and provide an opportunity to rule out models of leptogenesis which would otherwise evade direct detection experiments for effective eternity. Turning to the extreme temperature gradients of hot spots, the evolution and formation of hot spots was considered in an expanding background for the first time, and a formalism treating the propagation of Hawking radiation was introduced. Upon addressing the previously unexplored effects of hot spots on Hawking radiation, it was discovered that hot spots can support successful leptogenesis after sphaleron freeze-out, and efficiently absorb radiated Dark Matter. These examples hint at an intricate, rich tapestry of physics in hot spots.
Association of 220 PeV Neutrino KM3-230213A with Gamma-Ray Bursts
Recently, the KM3NeT Collaboration released the detection of a 220 PeV neutrino from the celestial coordinates RA=94.3\degree~ and Dec=-7.8\degree~ on 13 February 2023 at 01:16:47 UTC \cite{KM3NeT:2025npi}. The source for this extra-ordinary cosmic neutrino, designated KM3-230213A, is not identified yet but there has been a speculation that it might be associated with a gamma-ray burst GRB~090401B \cite{Amelino-Camelia:2025lqn}. The purpose of this report is to search the association of this 220 PeV neutrino with potential GRB sources from a more general consideration of Lorentz invariance violation (LV) without fixed LV scale. We try to associate this extra-ordinary neutrino with potential GRBs within angular separation of 1\degree, 3\degree~ and 5\degree~ respectively and the results are listed in Table 1. We find the constraints $E_{\rm{LV}}\leq 5.3\times 10^{18}$~GeV for subluminal LV violation and $E_{\rm{LV}}\leq 5.6\times 10^{19}$~GeV for superluminal LV violation if KM3-230213A is a GRB neutrino.
Scalar Field Static Spherically Symmetric Solutions in Teleparallel $F(T)$ Gravity
We investigate in this paper the static radial coordinate-dependent spherically symmetric spacetime in teleparallel $F(T)$ gravity for a scalar field source. We begin by setting the static field equations (FEs) to be solved and solve the conservation laws for scalar field potential solutions. We simplify the FEs and then find a general formula for computing the new teleparallel $F(T)$ solutions applicable for any scalar field potential $V(T)$ and coframe ansatz. We compute new non-trivial teleparallel $F(T)$ solutions by using a power-law coframe ansatz for each scalar potential case arising from the conservation laws. We apply this formula to find new exact teleparallel $F(T)$ solutions for several cases of coframe ansatz parameter. The new $F(T)$ solution classes will be relevant for {studying the models close to Born--Infeld and/or scalarized Black Hole (BH) solutions inside the} dark energy (DE) described by a fundamental scalar field such as quintessence, phantom energy or quintom system, to name only those types.
The Atacama Cosmology Telescope: DR6 Constraints on Extended Cosmological Models
We use new cosmic microwave background (CMB) primary temperature and polarization anisotropy measurements from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) to test foundational assumptions of the standard cosmological model and set constraints on extensions to it. We derive constraints from the ACT DR6 power spectra alone, as well as in combination with legacy data from Planck. To break geometric degeneracies, we include ACT and Planck CMB lensing data and baryon acoustic oscillation data from DESI Year-1, and further add supernovae measurements from Pantheon+ for models that affect the late-time expansion history. We verify the near-scale-invariance (running of the spectral index $d n_s/d\ln k = 0.0062 \pm 0.0052$) and adiabaticity of the primordial perturbations. Neutrino properties are consistent with Standard Model predictions: we find no evidence for new light, relativistic species that are free-streaming ($N_{\rm eff} = 2.86 \pm 0.13$, which combined with external BBN data becomes $N_{\rm eff} = 2.89 \pm 0.11$), for non-zero neutrino masses ($\sum m_\nu < 0.082$ eV at 95% CL), or for neutrino self-interactions. We also find no evidence for self-interacting dark radiation ($N_{\rm idr} < 0.134$), early-universe variation of fundamental constants, early dark energy, primordial magnetic fields, or modified recombination. Our data are consistent with standard BBN, the FIRAS-inferred CMB temperature, a dark matter component that is collisionless and with only a small fraction allowed as axion-like particles, a cosmological constant, and the late-time growth rate predicted by general relativity. We find no statistically significant preference for a departure from the baseline $\Lambda$CDM model. In general, models introduced to increase the Hubble constant or to decrease the amplitude of density fluctuations inferred from the primary CMB are not favored by our data.
Quantum thermal machines in BTZ black hole spacetime
We investigate an Otto thermodynamic cycle with a qubit Unruh-DeWitt detector as the working medium, coupled to a massless, conformally coupled scalar quantum field in the Hartle-Hawking vacuum in a (2+1)-dimensional BTZ black hole spacetime. We employ the thermal properties of the field to model heat and cold reservoirs between which the thermal machine operates. Treating the detector as an open quantum system, we employ a master equation to study its finite-time dynamics during each cycle stroke. We evaluate the output performance of the Otto heat engine and refrigerator by computing, respectively, the total work output and the cooling power for each of the Neumann, transparent, and Dirichlet boundary condition cases satisfied by the field at spatial infinity. Furthermore, we evaluate the optimal performance of the thermal machine by analyzing its efficiency at maximum power output and ecological impact. Our study presents a general framework for understanding the finite-time operation of relativistic quantum thermal machines, focusing on their energy optimization.
Relativistic stars in $f(Q)$-gravity
We investigate static spherically symmetric spacetimes within the framework of symmetric teleparallel $f(Q)$ gravity in order to describe relativistic stars. We adopt a specific ansatz for the background geometry corresponding to a singularity-free space-time. We obtain an expression for the connection, which allows the derivation of solutions for any $f(Q)$ theory in this context. Our approach aims to address a recurring error appearing in the literature, where even when a connection compatible with spherical symmetry is adopted, the field equation for the connection is systematically omitted and not checked if it is satisfied. For the stellar configuration, we concentrate on the power-law model $f(Q)=Q+\alpha Q_{0}\left( \frac{Q}{Q_{0}}\right) ^{\nu }$. The de Sitter-Schwarzschild geometry naturally emerges as an attractor beyond a certain radius, we thus utilize it as the external solution beyond the boundary of the star. We perform a detailed investigation of the physical characteristics of the interior solution, explicitly determining the mass function, analyzing the resulting gravitational fluid properties and deriving the angular and radial speed of sound.
Stable Wormholes in Conformal Gravity
We present a class of Lorentzian traversable wormholes in conformal gravity, constructed via Weyl rescaling of Minkowski spacetime. As a result, these wormholes are solutions of every theory of gravity that is both conformally invariant and admits Minkowski spacetime as a solution. We specifically examine the case of a wormhole possessing a Morris-Thorne shape function, arising as a solution of a scalar-tensor conformally invariant theory of gravity. We show that these solutions represent regular, traversable wormholes that are also stable at the linear perturbation level. We argue that, when the Weyl symmetry is spontaneously broken, the broken symmetry phase may lead to a stable ``wormhole phase" alternative to the flat ``Minkowski phase".
Gravitational-wave Extraction using Independent Component Analysis
Independent component analysis (ICA) is a method to extract a set of time-series data using "statistical independency" of each component. We propose applying ICA for extracting gravitational wave (GW) signals. Our idea is to extract a signal that is commonly included in multiple detectors and to find it by shifting the data-set around its arrival time. In this article, we show several tests using injected signals, and show that this method can be applied to events for signal-to-noise over 15. We then demonstrate the method to actual O1-O3 events, and the identification of the arrival time can be estimated more precisely than that was previously reported. This approach does not require templates of waveform, therefore it can be applied for testing general relativity, and also for finding unknown GW.
Non-Gaussianities as a Signature of Quantumness of Quantum Cosmology
We show that the consistent application of the rules of quantum mechanics to cosmological systems inevitably results in the so-called multiverse states in which neither the background spacetime nor the inhomogeneous perturbation are in definite states. We study the multiverse states as perturbations to the usually employed so-called Born-Oppenheimer states that are products of a wave function of the background and a wave function of the perturbation. The obtained corrections involve integrals over \emph{virtual backgrounds} that represent the effect of quantum background fluctuations on the perturbation state. They resemble loop corrections in quantum field theory. This approach demonstrates the inevitable existence of very specific non-Gaussian features in primordial fluctuations. We express the resulting non-Gaussian perturbation as a nonlinear function of the Gaussian perturbation obtained within the Born-Oppenheimer approximation, and compute its trispectrum, to show that the multiverse scenario leads to testable and distinct signatures in cosmological perturbations. Our approach applies both to inflationary and alternative cosmologies.
Emerging black hole shadow from collapsing boson star
This work devotes to investigate the dynamical emergence of black hole shadow from gravitational lensing in dynamical spacetime by using the collapsing boson star. Two characterized scenarios are adopted with or without considering the time delay of light propagation. As the boson star evolves, new Einstein rings emerge from the lensing center, with their radius gradually increasing, and their number continues to grow infinitely before the light-ring forms. The shadow forms instantaneously at the moment the black hole appears when ignoring the time delay of light propagation. Considering the time delay for light propagation in dynamical spacetime, a more intricate process of the shadow formation is uncovered: it first appears as a minute dot in the lensing center, then gradually grows as the black hole grows, eventually expands the inner region of the light-ring. During the quasi-stable phases of boson star and black hole, the lensing and shadow structures from two scenarios are nearly identical and remain almost unchanged. Our results present the universal dynamic patterns of the lensing and shadow structures, and reveal the potential observed phenomena near the collapsing star and the event horizon of the newly formed black hole.
Probing single-field inflation: predictions, constraints, and theoretical viewpoints
This work investigates a single-field inflationary model, a specific class of the K-essence models where a coupling term exists between canonical Lagrangian and the potential. This coupling term has many effects on key inflationary parameters consisting of the power spectral, the spectral index, the tensor-to-scalar ratio, the Hubble parameter, the equation of state parameter, and the slow-roll parameter. By solving the equations numerically and deriving analytical results, how this modification affects inflationary dynamics can be analyzed. Our results show that the coupling term, $\alpha$, decreases the inflationary parameters, such as the tensor-to-scalar ratio, $r$, and improves the consistency with observational constraints from Planck and BICEP/Keck at the $68 \%$ and $95 \%$ confidence. These findings indicate that the studied model provides a promising alternative to the early universe dynamics while aligning with recent cosmological observations.
Beyond holography: the entropic quantum gravity foundations of image processing
Recently, thanks to the development of artificial intelligence (AI) there is increasing scientific attention to establishing the connections between theoretical physics and AI. Traditionally, these connections have been focusing mostly on the relation between string theory and image processing and involve important theoretical paradigms such as holography. Recently G. Bianconi has proposed the entropic quantum gravity approach that proposes an action for gravity given by the quantum relative entropy between the metrics associated to a manifold. Here it is demonstrated that the famous Perona-Malik algorithm for image processing is the gradient flow of the entropic quantum gravity action. These results provide the geometrical and information theory foundations for the Perona-Malik algorithm and open new avenues for establishing fundamental relations between brain research, machine learning and entropic quantum gravity.
Over-Luminous Type Ia Supernovae and Standard Candle Cosmology
Type Ia supernovae (SNe Ia) serve as crucial cosmological distance indicators due to their empirical consistency in peak luminosity and characteristic light-curve decline rates. These properties facilitate them to be standardized candles for the determination of the Hubble constant ($H_0$) within late-time universe cosmology. Nevertheless, a statistically significant difference persists between $H_0$ values derived from early and late-time measurements, a phenomenon known as the Hubble tension. Furthermore, recent observations have identified a subset of over-luminous SNe Ia, characterized by peak luminosities exceeding the nominal range and faster decline rates. These discoveries raise questions regarding the reliability of SNe Ia as standard candles in measuring cosmological distances. In this article, we present the Bayesian analysis of eight over-luminous SNe Ia and show that they yield a lower $H_0$ estimates, exhibiting closer concordance with $H_0$ estimates derived from early-universe data. This investigation potentially represent a step toward addressing the Hubble tension.
Semiclassical Rotating AdS Black Holes with Quantum Hair in Holography
In the context of the AdS/CFT duality, we study semiclassical stationary rotating AdS black holes with non-trivial quantum hair in three and five dimensions. We construct these solutions by perturbing the BTZ black hole and the five-dimensional Myers-Perry AdS black hole according to holographic semiclassical equations. In the three-dimensional case, the vacuum expectation value of the stress-energy tensor diverges as $\sim 1/\lambda^n~(n=1,2)$ along a radial null geodesic as the affine parameter $\lambda$ approaches zero at the Cauchy horizon, depending on the type of perturbation. In the five-dimensional case, most hairy solutions exhibit strong divergences, either in the stress-energy tensor or in the parallelly propagated Riemann components, along the radial null geodesic crossing the Cauchy horizon. Nevertheless, there exists a specific class of semiclassical solutions that retain a $C^0$-regular Cauchy horizon, where perturbations remain bounded. For extremal black holes, the vacuum expectation value of the stress-energy tensor diverges along a radial null geodesic transverse to the event horizon in both three and five dimensions, even though all components of the perturbed metric vanish in this limit.
Innermost stable circular orbits around a Reissner-Nordström-global monopole spacetime in a homogeneous magnetic field
We investigate the dynamics of charged particles in the spacetime of a global monopole swallowed by a Reissner-Nordstr\"om (RN) black hole in the presence of a external weak asymptotically homogeneous magnetic field. We carefully analyze and deduce the conditions to have such a magnetic field around this black hole and show that this is indeed possible in the small but nontrivial charge and monopole term limit. We obtain general equations of motion and analyze them for special cases of circular orbits, focusing on the inner-most stable circular orbit (ISCO) of this configuration. The richness of the parameters and complicated forms of the resulting equations of motion necessitate a numerical approach. Hence, we have presented our results with numerous graphs, which help to understand the evolution of ISCO as a function of the external test magnetic field and the monopole term depending on the parameters of the black hole, such as its electrical charge as well as the properties of the test particle such as its specific charge, angular momentum, and energy. We have also analyzed the effective potential that these fields generate and deduced results for the aforementioned values of external and internal parameters of spacetime.
On the Explicit Asymptotic Symmetry Breaking of sl(3,R) Jackiw-Teitelboim Gravity
This study investigates the asymptotic symmetry algebras (ASA) of Jackiw-Teitelboim (JT) gravity within the framework of sl(3,R) symmetry. By explicitly constructing this algebra, we explore how the presence of the dilaton field influences the structure of asymptotic symmetries and symmetry breaking mechanisms at the AdS(2) boundary. For the sl(3,R) model, the dilaton field preserves a subset of the complete W(3)-symmetry, restricting the algebra to sl(3,R). These results provide deeper insights into the role of dilaton dynamics in holographic dualities, with implications for the thermodynamics and geometry of AdS(2). The findings pave the way for systematically exploring extended gauge symmetries in two-dimensional gravity and their relevance to higher-rank Lie algebras.
Regularizing the induced GW spectrum with dissipative effects
Finite mean free paths of light particles, like photons and neutrinos, lead to dissipative effects and damping of small-scale density fluctuations in the early universe. We study the impact of damping on the spectral density of gravitational waves induced by primordial fluctuations in the radiation-dominated universe. We show that the most important effects of damping are $(i)$ regularization of the resonant frequency and $(ii)$ a far low-frequency tail with no logarithmic running. The exact location of the break frequency below which the logarithmic running is lost depends on the damping rate. Both effects stem from the effective finite lifetime of the gravitational wave source caused by damping. Interestingly, we find that, for the standard model of particles, the effects of damping are most relevant at around or below the nHz frequencies. Our results showcase the importance of including the damping of primordial fluctuations in future analysis of induced gravitational waves. We provide detailed analytical formulas and approximations for the kernel of induced gravitational waves. Lastly, we discuss possible implications of damping in alleviating the gauge issue of induced gravitational waves and in suppressing the so-called poltergeist mechanism.
The unification of gravity and the spin-1 field
Unifying the massive spin-1 field with gravity requires the implementation of a regular vector field that satisfies the spin-1 Proca equation and is a fundamental part of the spacetime metric. That vector field is one of the pair of vectors in the line element field (\textbf{X},-\textbf{X}), which is paramount to the existence of all Lorentzian metrics and Modified General Relativity (MGR). Symmetrization of the spin-1 Klein-Gordon equation in a curved Lorentzian spacetime introduces the Lie derivative of the metric along the flow of one of the regular vectors in the line element field. The Proca equation in curved spacetime can then be described geometrically in terms of the line element vector, the Lie derivative of the Lorentzian metric, and the Ricci tensor, which unifies gravity and the spin-1 field. Related issues concerning charge conservation and the Lorenz constraint, singularities in a spherically symmetric curved spacetime, and geometrical implications of MGR to quantum theory are discussed. A geometrical unification of gravity with quantum field theory is presented.
Computational Framework for White Hole Detection in Gravitational Waves and CMB Data
This study presents a computational framework for evaluating the detectability of white hole-induced gravitational wave signals and their imprints on the cosmic microwave background (CMB). The approach integrates stochastic gravitational wave background (SGWB) polarization data from LISA with CMB-S4 B-mode anisotropies, utilizing Monte Carlo simulations, Bayesian inference, and signal-to-noise ratio (SNR) estimations to determine detection feasibility.
Wavefunction coefficients from Amplitubes
Given a graph its set of connected subgraphs (tubes) can be defined in two ways: either by considering subsets of edges, or by considering subsets of vertices. We refer to these as binary tubes and unary tubes respectively. Both notions come with a natural compatibility condition between tubes which differ by a simple adjacency constraint. Compatible sets of tubes are refered to as tubings. By considering the set of binary tubes, and summing over all maximal binary-tubings, one is lead to an expression for the flat space wavefunction coefficients relevant for computing cosmological correlators. On the other hand, considering the set of unary tubes, and summing over all maximal unary-tubings, one is lead to expressions recently referred to as amplitubes which resemble the scattering amplitudes of $\text{tr}(\phi^3)$ theory. In this paper we study the two definitions of tubing in order to provide a new formula for the flat space wavefunction coefficient for a single graph as a sum over products of amplitubes. We also show how the expressions for the amplitubes can naturally be understood as a sum over orientations of the underlying graph. Motivated by our rewriting of the wavefunction coefficient we introduce a new definition of tubing which makes use of both the binary and unary tubes which we refer to as cut tubings. We explain how each cut tubing induces a decorated orientation of the underlying graph and demonstrate how the set of all decorated orientations for a given graph count the number of basis functions appearing in the kinematic flow.
Microstates of Non-extremal Black Holes: A New Hope
We provide a new roadmap for constructing microstates of non-extremal black holes in supergravity. First, we review the non-linear sigma model of five-dimensional supergravity governing stationary solutions with a U(1) isometry and present the first generalized Ernst formulation of this model. We then revisit solution-generating techniques associated to the coset model symmetry, Ernst formalism and inverse scattering method. While some of these techniques have been extensively used to generate non-extremal black holes and black rings in supergravity, we demonstrate how they can be adapted to construct systematically non-BPS smooth horizonless geometries that have the same mass and charges as non-extremal black holes. To illustrate these methods, we construct novel static solutions of this type, including a non-BPS generalization of the $\frac{1}{2}$-BPS Gibbons-Hawking center, which has served as the fundamental building block of multicenter microstates of BPS black holes.
Gravitational Wave Scattering via the Born Series: Scalar Tidal Matching to $\mathcal{O}(G^7)$ and Beyond
We introduce a novel method to compute gravitational wave amplitudes within the framework of effective field theory. By reinterpreting the Feynman diagram expansion as a Born series, our method offers several key advantages. It directly yields partial wave amplitudes, streamlining the matching with black hole perturbation theory. Long-distance gravitational interactions are unambiguously factorized from short-distance tidal effects, including dissipation, which are systematically incorporated via an in-in worldline effective action. Crucially, at every order in perturbation theory, integrals are expressed in terms of harmonic polylogarithms, enabling an end-to-end computation scalable to arbitrary orders. We illustrate the method with new predictions for scalar black hole Love numbers and their Renormalization Group equations to $\mathcal{O}(G^7)$.
Black-hole binaries and waveforms in Quadratic Gravity
We report on the first numerical-relativity simulations of black-hole binaries that deviate from General Relativity due to quadratic-curvature corrections. Said theory of Quadratic Gravity propagates additional massive modes and admits both Kerr and non-Kerr black-hole solutions. We chose the respective masses "at threshold", i.e., such that (at least) one of the black holes dynamically transitions from the Kerr to the non-Kerr branch during the early inspiral. The subsequent waveforms differ from their General Relativity counterparts throughout inspiral, merger, and ringdown.
Spacetime Structure of Regular Accelerating Black Hole Pair in General Relativity
We revisit the one-parameter generalization of the C-metric derived by Ernst, which solves the vacuum Einstein equations. Resolving conflicting claims in the literature, we determine the correct value of the parameter that ensures the regularity of the metric on the axis. This "regularized C-metric" describes a pair of accelerating black holes without the line source present in the original C-metric. Additionally, this generalization changes the Petrov type from D to I. We use the Gauss-Bonnet theorem to analyze the nodal singularities, the line source, and their relation to the horizon topology. Both the black hole and acceleration horizons are found to be embeddable in $\mathrm{E}^3$. We examine various geometric and asymptotic properties in detail using several coordinate systems and construct the corresponding 2D and 3D conformal diagrams. This process is more involved than for the original C-metric due to the presence of the exponential factors. These exponential factors also introduce curvature singularities at infinity, which obstructs asymptotic flatness. Contrary to Bonnor's expectation, we demonstrate why Bondi's algorithm for obtaining the standard Bondi form fails for the C-metric, despite its asymptotic flatness. We also show that Ernst's solution-generating prescription in boost-rotation symmetric coordinates is a symmetry of the wave equation.
Black holes inside cosmic voids
This study examines the gravitational and thermodynamic properties of static, spherically symmetric black holes within cosmic voids -- vast underdense regions of the universe. By deriving a novel solution based on a universal density profile for voids, we analyze its spacetime structure, which reveals two horizons: One of the black hole and the other related to the de Sitter-like behavior. As the void approaches a perfect vacuum, the black hole horizon diminishes, tending to that of the Schwarzschild solution, while the outer horizon increases. We also study the solution stability via sound speed of the fluid, as well as the thermodynamic properties, including Hawking temperature, evaporation time, entropy, and specific heat. Our results show that as the void empties, the Hawking temperature rises, shortening evaporation times. The entropy follows the area's law and specific heat exhibits a minimum for a given black hole size, indicating a thermal transition and highlighting the role of voids in the black hole evolution. These findings offer new insights into the relationship between local gravitational collapse and large-scale cosmic structure, enhancing our understanding of the black hole behavior in underdense environments. We also provide a glimpse of a potential thermodynamic interaction between the event horizon and the cosmological horizon.
Exploring Scalarized Einstein-Gauss-Bonnet Theories Through the Lens of Parametrized Post-Newtonian Formalism
We explore scalarized Einstein-Gauss-Bonnet theories within the context of the Parameterized Post-Newtonian formalism, which serves as a robust framework for examining modifications to General Relativity that exhibit scalarization. This approach enables us to impose a variety of constraints on the parameter space, particularly focusing on the PPN parameters $\gamma$ and $\beta$. Our analysis reveals several significant bounds for each scalarized model, utilizing data from the Cassini mission, Lunar Laser Ranging, and the forthcoming BepiColombo mission, in conjunction with geodetic Very Long Baseline Interferometry measurements around the Sun. In particular, we conducted a combined analysis of the MESSENGER mission's precision measurements of Mercury's perihelion precession $\dot{\omega}$ alongside the Cassini constraints on $\gamma$, yielding intriguing limits for the Ricci-EGB model. Furthermore, we investigate the impact of the new post-Newtonian potential introduced by the Gauss-Bonnet term at fourth order, which necessitates an expanded formulation of the PPN parameters. This highlights that the parameter $\beta$ exhibits different effects when analyzing the Ricci-EGB model. Additional constraints are derived from this framework by estimating the $\gamma$ PPN parameter using data from strong-lensing galaxy systems.
Extended mass and spheroidal deformation effects on epicyclic frequencies and periapsis shift in quasi-circular orbits
We investigate the effects of extended mass and spheroidal deformation on the periapsis shift of quasi-circular orbits inside a gravitating mass distribution in the Newtonian framework. Focusing on the internal gravitational potential of a spheroidal body with both homogeneous and inhomogeneous density profiles, we elucidate how the ratio of local density to average density governs the extended mass effect on the periapsis shift. By analyzing the orbital angular frequency, along with the radial and vertical epicyclic frequencies, we demonstrate that in the uniform density case (i.e., the Maclaurin spheroid), where the potential takes the form of a harmonic oscillator, the periapsis exhibits a constant retrograde shift of $-\pi$. In contrast, in regions where density inhomogeneity and spheroidal deformation (in both prolate and oblate forms) are significant, the periapsis shift varies with the guiding orbital radius due to local density contrast and deformation effects. The resuls indicate that oblate deformation suppresses the extended mass effect associated with the ratio of local density to average density, whereas prolate deformation amplifies it. Furthermore, by varying the density distribution parameters, we establish the conditions for orbital stability and identify the emergence of marginally stable orbits.
Rotating black holes in a class of scalar-Gauss-Bonnet gravity
In this study, we investigate rotating black hole solutions within a scalar Gauss Bonnet gravity framework that incorporates a quadratic Gauss Bonnet term. By employing a quadratic exponential coupling function between the scalar field and the Gauss Bonnet invariant, we derive both the standard General Relativity solutions and novel scalarized black hole configurations. Utilizing a pseudo spectral method to solve the coupled field equations, we examine how black hole spin and coupling constants influence the existence and properties of these solutions. Our findings reveal that both the rotation of the black hole and the quadratic coupling term effectively constrain the parameter space available for scalarization. Moreover, we demonstrate that, over a wide range of parameters, scalarized black holes exhibit higher entropy than Kerr black holes of equivalent mass and spin, indicating that they are thermodynamically favored. These results significantly expand the phase space of black holes in modified gravity theories.
Distorted black holes: a characteristic view
We investigate the interaction between a non-rotating black hole and incoming gravitational waves using the characteristic formulation of the Einstein field equations, framed as a Bondi problem. By adopting retarded time as the null coordinate and recognizing that the final state is invariably a black hole, we demonstrate that an apparent horizon forms once sufficient mass accretes onto the black hole. We derive the evolution of the Bondi mass and compute its final value, enabling us to quantify the fraction of the incident mass absorbed by the black hole. Additionally, we establish a scaling law for the absorbed mass as a function of initial parameters, such as the amplitude of the gravitational wave data. Furthermore, we explore the dynamics when a reflecting barrier surrounds the black hole. For low-amplitude initial waves, the barrier reflects the waves, leaving the original black hole as the end state. Conversely, high-amplitude waves lead to the formation of an apparent horizon that engulfs the barrier, producing a new, larger black hole.
On black holes in teleparallel torsion theories of gravity
We first present an overview of the Schwarzschild vacuum spacetime within general relativity, with particular emphasis on the role of scalar polynomial invariants and the null frame approach (and the related Cartan invariants), that justifies the conventional interpretation of the Schwarzschild geometry as a black hole spacetime admitting a horizon (at $r=2M$ in Schwarzschild coordinates) shielding a singular point at the origin. We then consider static spherical symmetric vacuum teleparallel spacetimes in which the torsion characterizes the geometry, and the scalar invariants of interest are those constructed from the torsion and its (covariant) derivatives. We investigate the Schwarzschild-like spacetime in the teleparallel equivalent of general relativity and find that the torsion scalar invariants (and, in particular, the scalar $T$) diverge at the putative ``Schwarzschild'' horizon. In this sense the resulting spacetime is {\em not} a black hole spacetime. We then briefly consider the Kerr-like solution in the teleparallel equivalent of general relativity and obtain a similar result. Finally, we investigate static spherically symmetric vacuum spacetimes within the more general $F(T)$ teleparallel gravity and show that if a such a geometry admits a horizon, then the torsion scalar $T$ necessarily diverges there; consequently in this sense such a geometry also does {\em not} represent a black hole.
Standard Model Symmetries and K(E_10)
We clarify and extend our earlier work (K.A.Meissner and H.Nicolai, Phys. Rev. D91 (2015) 065029 and Phys. Rev. Lett. 121 (2018) 091601) where it was shown how to amend a scheme originally proposed by M. Gell-Mann to identify the three families of quarks and leptons of the Standard Model with the 48 spin 1/2 fermions of N=8 supergravity that remain after absorption of eight Goldstinos, a scheme that in its original form is dynamically realized at the SU(3)xU(1) stationary point of gauged N=8 supergravity. We explain how to deform and enlarge this symmetry at the kinematical level to the full Standard Model symmetry group SU(3)_c x SU(2)_w x U(1)_Y, with the correct charge and chiral assignments for all fermions. The framework also leaves room for an extra U(1)_(B-L) symmetry. This symmetry enhancement is achieved by embedding the Standard Model symmetries into (a quotient group of) K(E_10), the `maximal compact subgroup' of the maximal rank hyperbolic Kac-Moody symmetry E_10, and an infinite prolongation of the SU(8) R-symmetry of N=8 supergravity. This scheme, which is also supposed to encompass quantum gravity, cannot be realized within the framework of space-time based (quantum) field theory, but requires space-time and related geometrical concepts to be `emergent'. We critically review the main hypotheses underlying this construction.
Regular black holes and their singular families
Regular black holes without curvature singularity can arise in Einstein gravity with appropriate matter energy-momentum tensor. We show that these regular solutions represent only a special case of a much broader family of black holes with a free mass parameter. The regularity is achieved only at a specific mass value, and any deviation from the fine-tuned parameter inevitably results in curvature singularity. As a concrete example, we consider nonlinear electrodynamics (NLED) as matter sources. A new NLED theory is proposed that is a generalization of the Bardeen class and the Hayward class. New regular black holes and their singular counterparts are obtained. Significant distinctions between regular black holes and their singular counterparts are analyzed. These findings provide new insights into regular black holes.
Gravitational Wave Effects on Radio Spectral Lines of Atomic Hydrogen: Hyperfine Splitting and Broadening Mechanisms
We explore the effects of gravitational waves (GWs) on hydrogen's radio spectral lines, focusing on the ground-state hyperfine transition and radiative transitions in highly excited Rydberg states. To analyze GW impacts on hyperfine structure, we derive Maxwell's equations in a gravitational-wave background using linearized gravity and the $3+1$ formalism. Our findings reveal that GWs induce energy shifts in hyperfine magnetic substates, modifying the 21 cm line. However, these energy shifts fall well below the detection limits of current radio astronomical instruments. For transitions in highly excited states, which produce radio recombination lines (RRL), the influence of GW manifests itself as spectral broadening, with the fractional linewidth for $\mathrm{H}n\alpha$ scaling as $\Delta\nu/\nu_0 \sim n^7\omega^2_{\mathrm{gw}}h(t)$. This suggests that RRLs could serve as probes for ultra-high-frequency GWs, particularly given that Rydberg atoms in the interstellar medium can reach quantum numbers above $n=100$. As an example of possibly detectable high frequency GW source, We investigate GWs emitted during the inspiral of planetary-mass primordial black hole binaries, where GW-induced broadening in RRLs could exceed natural broadening effects. Additionally, we examine the influence of the recently detected stochastic gravitational-wave background on hydrogen spectral lines.
Time-domain phenomenological multipolar waveforms for aligned-spin binary black holes in elliptical orbits
We introduce IMRPhenomTEHM, a new phenomenological time-domain model for eccentric aligned-spin binary black holes. Building upon the accurate quasi-circular IMRPhenomTHM model, IMRPhenomTEHM integrates the eccentric post-Newtonian (PN) dynamics and introduces eccentric corrections into the waveform multipoles up to 3PN, including spin effects. The model incorporates the dominant (2, $\pm$2) spherical harmonic mode, as well as the subdominant modes (2, $\pm$1), (3, $\pm$3), (4, $\pm$4), and (5, $\pm$5), assuming the binary has circularized by the time of merger. This approach ensures a smooth transition to the non-eccentric limit, providing an accurate quasi-circular limit against the IMRPhenomTHM model. When comparing against 28 public eccentric numerical relativity simulations from the Simulating eXtreme Spacetimes catalog, IMRPhenomTEHM achieves lower than 2% unfaithfulness, confirming its accurate description without calibration to numerical relativity eccentric datasets. IMRPhenomTEHM provides a reliable description of the evolution of eccentric black hole binaries with aligned spins and eccentricities lower than $e=0.4$ at a frequency of 10 Hz, making it suitable for upcoming gravitational-wave observing runs. We validate the model's accuracy through parameter estimation studies, recovering injected parameters within 90% credible intervals for three numerical relativity eccentric simulations and reanalyzing GW150914 and GW190521, obtaining results consistent with the literature.
Neutrino Decoherence in \texorpdfstring{\(κ\)}{kappa}-Minkowski Quantum Spacetime: An Open Quantum Systems Paradigm
We investigate neutrino decoherence within the framework of quantum spacetime, focusing on the $\kappa$-Minkowski model. We show that stochastic fluctuations in quantum spacetime induce an energy-dependent decoherence effect, where the decoherence rate scales as $E^{-4}$. This result aligns with recent IceCube observations, indicating that quantum gravity does not induce significant decoherence for high-energy neutrinos. Additionally, we establish conditions under which quantum spacetime effects could influence relic neutrinos, such as those in the cosmic neutrino background ($C\nu B$). Our results shed light on how quantum spacetime fluctuations impact neutrino oscillation physics.
Initial acquisition requirements for optical cavities in the space gravitational wave antennae DECIGO and B-DECIGO
DECIGO (DECi-hertz Interferometer Gravitational Wave Observatory) is a space-based gravitational wave antenna concept targeting the 0.1-10 Hz band. It consists of three spacecraft arranged in an equilateral triangle with 1,000 km sides, forming Fabry-P\'erot cavities between them. A precursor mission, B-DECIGO, is also planned, featuring a smaller 100 km triangle. Operating these cavities requires ultra-precise formation flying, where inter-mirror distance and alignment must be precisely controlled. Achieving this necessitates a sequential improvement in precision using various sensors and actuators, from the deployment of the spacecraft to laser link acquisition and ultimately to the control of the Fabry-P\'erot cavities to maintain resonance. In this paper, we derive the precision requirements at each stage and discuss the feasibility of achieving them. We show that the relative speed between cavity mirrors must be controlled at the sub-micrometer-per-second level and that relative alignment must be maintained at the sub-microradian level to obtain control signals from the Fabry-P\'erot cavities of DECIGO and B-DECIGO.
Dynamics of Spinning Particles in Reissner-Nordström black hole exterior
We study the orbits of a spinning particle in the Reissner-Nordstr\"om black hole exterior through the spin-curvature coupling to leading order in its spin. The dynamics is governed by the Mathisson-Papapetrou equations in the pole-dipole approximation. The equations of motion can be derived and show in particular that in the polar coordinate, the orbits can be restricted to the plane for an aligned spin with the orbital motion, but there is an induced motion out of the plane for a misaligned spin. The radial potential can be defined from the equation of motion along the radial direction, where the roots are studied to construct the parameter space diagram for different types of orbits. We then consider the so-called innermost stable circular orbit (ISCO) due to the triple root to see the effects of the particle spin and the black hole charge. These non-geodesic equations can be solved analytically in terms of the Mino time with the solutions involving Jacobi elliptic functions. One of the bound motions considered is an oscillating orbit between two turning points in the radial direction. The usefulness of the solutions is to obtain the periods of the oscillation along the radial direction as well as the induced motion in the polar coordinate for a misaligned spin in both the Mino time and the coordinate time. Another interesting motions include the inspiral orbit from near ISCO and the homoclinic orbit with the solutions expressed as elementary functions, giving the radial 4-velocity of the inspiral orbit and the Lyapunov exponent associated with the homoclinic orbit. The implications for gravitational wave emission from extreme mass-ratio inspirals (EMRIs) and black hole accretion are discussed.
Constraints on violation of Lorentz symmetry with clock-comparison redshift experiments
Lorentz symmetry is a cornerstone of both the General relativity and Standard Model and its experimental verification deepens our understanding of nature. This paper focuses on the investigation of Lorentz violations with the context of clock comparison experiments in the framework of Standard Model Extension (SME). Considering matter-gravity coupling sector, we provide a generic frame to study the sensitivities of Lorentz-violating coefficients for three distinct types of clock redshift tests, including the traditional gravitational redshift test, null-redshift test I and null-redshift test II. Each of these tests is sensitivity to different combinations of Lorentz-violating coefficients. By using the current clock comparison results, we estimate the limits of SME coefficients at level of parts in $10^{4}$ down to parts in $10^{7}$. Better sensitivity may be achieved in the clock comparisons by using the state-of-the-art optical clocks. Additionally considering relativistic factors in null-redshift I, the frequency comparison result of E2 and E3 transitions of Yb$^{+}$ can set the limit $c^{e}_{00}=(7.4\pm9.3)\times10^{-9}$ in the electron sector. Our analysis demonstrates that clock-comparison redshift experiments may contribute to explore the vast parameters space on searching for the Lorentz violation.
Active and Passive Conformal Transformations in Scalar-Tensor Gravitational Theories
Through considering the conformal transformations as coordinate transformations in some abstract space of fields, where the different fields are assumed as ``generalized coordinates,'' we introduce the notion of active and passive conformal transformations. We then apply both complementary approaches to the conformal frames issue, arising in the context of scalar-tensor gravity theories, in order to get better understanding of the problem. Special focus is on the coupling of matter fields to gravity. The recent result that the Lagrangian density of fundamental matter fields and perfect fluids is not only conformal invariant but also conformal form-invariant is discussed within the context of the conformal frames issue.
