Tests of general relativity with gravitational waves typically introduce parameters for putative deviations and combine information from multiple events by characterizing the population distribution of these parameters through a hierarchical model. Although many tests include multiple such parameters, hierarchical tests have so far been unable to accommodate this multidimensionality, instead restricting to separate one-dimensional analyses and discarding information about parameter correlations. In this paper, we extend population tests of general relativity to handle an arbitrary number of dimensions. We demonstrate this framework on the two-dimensional inspiral-merger-ringdown consistency test, and derive new constraints from the latest LIGO-Virgo-KAGRA catalog, GWTC-3. We obtain joint constraints for the two parameters introduced by the classic formulation of this test, revealing their correlation structure both at the individual-event and population levels. We additionally propose a new four-dimensional formulation of the inspiral-merger-ringdown test that we show contains further information. As in past work, we find the GW190814 event to be an outlier; the 4D analysis yields further insights on how the low mass and spin of this event biases the population results. Without (with) this event, we find consistency with general relativity at the 60% (92%) credible level in the 2D formulation, and 76% (80%) for the 4D formulation. This multidimensional framework can be immediately applied to other tests of general relativity in any number of dimensions, including the parametrized post-Einsteinian tests and ringdown tests.

The pulsar timings are sensitive to both the nanohertz gravitational-wave background and the oscillation of ultralight dark matter. The Hellings-Downs angular correlation curve provides a criterion to search for stochastic gravitational-wave backgrounds at nanohertz via pulsar timing arrays. We study the angular correlation of the timing residuals induced by the spin-2 ultralight dark matter, which is different from the usual Hellings-Downs correlation. At a typical frequency, we show that the spin-2 ultralight dark matter can give rise to the deformation of the Hellings-Downs correlation curve induced by the stochastic gravitational wave background.

Short-duration noise transients in LIGO and Virgo detectors significantly affect the search sensitivity of compact binary coalescence (CBC) signals, especially in the high-mass region. In a previous work by the authors [P. Joshi et al., Phys. Rev. D 103, 044035 (2021)], a ${\chi }^2$ statistic was proposed to distinguish them, when modeled as sine-Gaussians, from nonspinning CBCs. The present work is an extension where we demonstrate the better noise-discrimination of an improved ${\chi }^2$ statistic—called the optimized sine-Gaussian ${\chi }^2$—in real LIGO data. The extension includes accounting for the initial phase of the noise transients and use of a well-informed choice of sine-Gaussian basis vectors selected to discern how CBC signals and some of the most worrisome noise transients project differently on them [S. Choudhary et al., Phys. Rev. D 107, 024030 (2023)]. To demonstrate this improvement, we use data with blip glitches from the third observational run (O3) of LIGO-Hanford and LIGO-Livingston detectors. Blips are a type of short-duration non-Gaussian noise disturbance known to adversely affect high-mass CBC searches. For CBCs, spin-aligned binary black hole signals were simulated using the imrphenompv2 waveform and injected into real LIGO data from the same run. We show that in comparison to the sine-Gaussian ${\chi }^2$, the optimized sine-Gaussian ${\chi }^2$ improves the overall true positive rate by around 6% in a lower-mass bin ($m_1,m_2\in [20,40]M_{\odot }$) and by more than 3% in a higher-mass bin ($m_1,m_2\in [60,80]M_{\odot }$). On the other hand, we see a larger improvement—of more than 20%—in both mass bins in comparison to the traditional ${\chi }^2$.

We show that when the Wald-Zoupas prescription is implemented, the resulting charges realize the Bondi-Van der Burg–Metzner-Sachs (BMS) symmetry algebra without any 2-cocycle nor central extension, at any cut of future null infinity. We refine the covariance prescription for application to the charge aspects, and introduce a new aspect for Geroch’s supermomentum with better covariance properties. For the extended BMS symmetry with singular conformal Killing vectors we find that a Wald-Zoupas symplectic potential exists, if one is willing to modify the symplectic structure by a corner term. The resulting algebra of Noether currents between two arbitrary cuts is centerless. The charge algebra at a given cut has a residual field-dependent 2-cocycle, but time-independent and nonradiative. More precisely, superrotation fluxes act covariantly, but superrotation charges act covariantly only on global translations. The take home message is that in any situation where 2-cocycles appears in the literature, covariance has likely been lost in the charge prescription, and that the criterium of covariance is a powerful one to reduce ambiguities in the charges, and can be used also for ambiguities in the charge aspects.

We introduce a Hamiltonian framework tailored to degrees of freedom (DOF) of field theories that reside in suitable 3-dimensional open regions, and then apply it to the gravitational DOF of general relativity. Specifically, these DOF now refer to open regions $\widehat{\mathcal{R}}$ of null infinity ${ℐ}^{+}$, and $R$ of black hole (and cosmological) horizons $\mathrm{\Delta }$ representing equilibrium situations. At ${ℐ}^{+}$ the new Hamiltonian framework yields the well-known BMS fluxes and charges. By contrast, all fluxes vanish identically at $\mathrm{\Delta }$ just as one would physically expect. In the companion paper [Phys. Rev. D 110, 044048 (2024).] we showed that, somewhat surprisingly, the geometry and symmetries of ${ℐ}^{+}$ and $\mathrm{\Delta }$ descend from a common framework. This paper reinforces that theme: Very different physics emerges in the two cases from a common Hamiltonian framework because of the difference in the nature of degrees of freedom on ${ℐ}^{+}$ and $\mathrm{\Delta }$, discussed in the companion paper. Finally, we compare and contrast this Hamiltonian approach with those available in the literature.

Null infinity, ${\mathcal{I}}^{+}$, arises as a boundary of the Penrose conformal completion $(\widehat{M},{\widehat{g}}_{ab})$ of an asymptotically flat physical space-time $(M,g_{ab})$. We first note that ${\mathcal{I}}^{+}$ is a weakly isolated horizon (WIH) in $(\widehat{M},{\widehat{g}}_{ab})$, and then show that its familiar geometric properties can be derived from the general WIH framework. This seems quite surprising because physics associated with black hole (and cosmological) WIHs $\mathrm{\Delta }$ is very different from that extracted at ${\mathcal{I}}^{+}$. We show that these differences can be directly traced back to the fact that ${\mathcal{I}}^{+}$ is a WIH in the conformal completion rather than the physical space-time. In particular, the BMS group at ${\mathcal{I}}^{+}$ stems from the symmetry group of WIHs. In a companion paper [Phys. Rev. D 110, 044049 (2024).] we obtain fluxes and charges associated with symmetries associated with ${\mathcal{I}}^{+}$ and $\mathrm{\Delta }$ using a new Hamiltonian framework. The fact that is there is a single mathematical framework underlying $\mathrm{\Delta }$ and ${\mathcal{I}}^{+}$ paves the way to explore the relation between horizon dynamics in the strong field region and waveforms at infinity. It should also be useful in the analysis of black hole evaporation in quantum gravity.

We explore the possibility of producing the observed matter-antimatter asymmetry of the Universe uniquely from the evaporation of primordial black holes (PBHs) that are formed in an inflaton-dominated background. Considering the inflaton $(\varphi )$ to oscillate in a monomial potential $V(\varphi )\propto {\varphi }^n$, we show, it is possible to obtain the desired baryon asymmetry via vanilla leptogenesis from evaporating PBHs of initial mass $\lesssim 10\mathrm{g}$. We find that the allowed parameter space is heavily dependent on the shape of the inflaton potential during reheating (determined by the exponent of the potential $n$), the energy density of PBHs (determined by $\beta$), and the nature of the coupling between the inflaton and the Standard Model. To complete the minimal gravitational framework, we also include in our analysis the gravitational leptogenesis setup through inflaton scattering via exchange of graviton, which opens up an even larger window for PBH mass, depending on the background equation of state. We finally illustrate that such gravitational leptogenesis scenarios can be tested with upcoming gravitational wave (GW) detectors, courtesy of the blue-tilted primordial GW with inflationary origin, thus paving a way to probe a PBH-induced reheating together with leptogenesis.

In this paper we consider a general theory of $k$-inflation and find out that it may be in a strong coupling regime. We derive accurate conditions of classical description validity using unitarity bounds for this model. Next, we choose a simple toy model of $k$-inflation and obtain the explicit condition, which guarantees that the generation of perturbations is performed in a controllable way, i.e., the exit from the effective horizon occurs in the weak coupling regime. However, for the same toy model the corresponding experimental bounds on a nonlinear parameter $f_{\mathrm{NL}}^{\text{equil}}$ associated with non-Gaussianities of the curvature perturbation provide much stronger constraint than strong coupling absence condition. Nevertheless, for other known models of inflation this may not be the case. Generally, one should always check if classical description is legitimate for chosen models of inflation.

We perform the numerical simulation of primordial black hole (PBH) formation from a nonspherical profile of the initial curvature perturbation $\zeta$. We consider the background expanding universe filled with the perfect fluid with the linear equation of state $p=w\rho$ ($w=1/3$ or $1/5$), where $p$ and $\rho$ are the pressure and the energy density, respectively. The initial condition is set in a way such that the principal directions of the second derivatives of $\zeta$ and $\mathrm{\Delta }\zeta$ at the central peak are misaligned, where $\mathrm{\Delta }$ is the Laplacian. In this setting, since the linearized density is proportional to $\mathrm{\Delta }\zeta$, the inertia tensor and deformation tensor ${\partial }_i{\partial }_j\zeta$ are misaligned. Thus, tidal torque may act, and the spin of a resultant primordial black hole would be nonzero, in general, although it is estimated to be very small from previous perturbative analyses. As a result, we do not find a finite value of the spin within our numerical precision, giving support for the negligibly small value of the black hole spin for $1/5\lesssim w\lesssim 1/3$. More specifically, our results suggest that the dimensionless PBH spin $s$ is typically so small that $s\ll 0.1$ for $w\gtrsim 0.2$.

Real-time measurements are becoming feasible in cosmology, where the next generation of telescopes will detect the temporal change of redshifts and sky positions of individual sources with a precision that will allow a direct detection of the cosmic expansion rate. These detections of cosmic drifts of redshifts and positions are likely to become cornerstones in modern cosmology, where one has otherwise relied on the indirect inference of cosmic expansion by estimation of the slope of the fitted distance–redshift relation. Because of their ability to directly detect the cosmic time evolution, real-time measurements are powerful as model-independent probes. We develop a cosmographic framework for analyzing cosmological redshift drift and position drift signals without knowledge of the space-time geometry. The framework can be applied to analyze data from surveys such as the Gaia observatory, the Square Kilometer Array, and the Extremely Large Telescope. The drift effects are distorted by the regional kinematics and tidal effects in the cosmic neighborhood of the observer, giving rise to nontrivial corrections to the well-known Friedmann-Lemaître-Robertson-Walker results. We discuss how one may concretely implement the framework in the statistical analysis of real-time data, along with assumptions and limitations that come with such an analysis. We also discuss the geometrical information that can ideally be extracted from ideal high-resolution data of cosmic drifts in combination with distance–redshift data.

Tidal disruptions of stars on the equatorial plane orbiting Kerr black holes have been widely studied. However, thus far, there have been fewer studies of stars in inclined precessing orbits around a Kerr black hole. In this paper, we use the tensor virial equations to show the presence of possible resonances in these systems for typical physical parameters of black hole–neutron star binaries in close orbits or of a white dwarf/an ordinary star orbiting a supermassive black hole. This suggests the presence of a new instability before the tidal disruption limit is encountered in such systems.

We study the prospects for measuring the time variation of solar and atmospheric neutrino fluxes at future large-scale xenon and argon dark matter detectors. For solar neutrinos, a yearly time variation arises from the eccentricity of Earth’s orbit and, for charged current interactions, from a smaller energy-dependent day-night variation due to flavor regeneration as neutrinos travel through Earth. For a 100-ton xenon detector running for ten years with a xenon-136 fraction of $\lesssim 0.1\%$, in the electron recoil channel a time-variation amplitude of about 0.8% is detectable with a power of 90% and the level of significance of 10%. This is sufficient to detect time variation due to eccentricity, which has amplitude of $\sim 3\%$. In the nuclear recoil channel, the detectable amplitude is about 10% under current detector resolution and efficiency conditions, and this generally reduces to about 1% for improved detector resolution and efficiency, the latter of which is sufficient to detect time variation due to eccentricity. Our analysis assumes both known and unknown periods. We provide scalings to determine the sensitivity to an arbitrary time-varying amplitude as a function of detector parameters. Identifying the time variation of the neutrino fluxes will be important for distinguishing neutrinos from dark matter signals and other detector-related backgrounds and extracting properties of neutrinos that can be uniquely studied in dark matter experiments.

Maximizing the number of detections in matched filter searches for compact binary coalescence (CBC) gravitational wave signals requires a model of the source population distribution. In previous searches using the pycbc framework, sensitivity to the population of binary black hole (BBH) mergers was improved by restricting the range of filter template mass ratios and use of a simple one-dimensional population model. However, this approach does not make use of our full knowledge of the population and cannot be extended to a full parameter space search. Here, we introduce a new ranking method, based on kernel density estimation with adaptive bandwidth, to accurately model the probability distributions of binary source parameters over a template bank, both for signals and for noise events. We demonstrate this ranking method by conducting a search over LIGO-Virgo O3 data for BBHs with unrestricted mass ratio, using a signal model derived from previous significant detected events. We achieve over 10% increase in sensitive volume for a simple power-law simulated signal population, compared to the previous BBH search. Correspondingly, with the new ranking, eight additional candidate events above an inverse false alarm rate threshold 0.5 yr are identified.

Gravitational-wave analyses depend heavily on waveforms that model the evolution of compact binary coalescences as seen by observing detectors. In many cases these waveforms are given by waveform approximants, models that approximate the amplitude and phase of the waveform at a set of frequencies. Because of their omnipresence, improving the speed at which approximants can generate waveforms is crucial to accelerating the overall analysis of gravitational-wave detections. An optimization algorithm is proposed that can select at which frequencies in the spectrum an approximant should compute the power of a waveform, and at which frequencies the power can be safely interpolated at a minor loss in accuracy. The algorithm used is an evolutionary algorithm modeled after the principle of natural selection, iterating frequency arrays that perform better at every iteration. As an application, the candidates proposed by the algorithm are used to reconstruct signal-to-noise ratios. It is shown that the imrphenomxphm approximant can be sped up by at least 30% at a loss of at most 2.87% on the drawn samples, measured by the accuracy of the reconstruction of signal-to-noise ratios. The behavior of the algorithm as well as lower bounds on both speedup and error are explored, leading to a proposed proof of concept candidate that obtains a speedup of 46% with a maximum error of 0.5% on a sample of the parameter space used.

We examine the thin accretion disk behaviors surrounding black holes embedded in cold dark matter halos and scalar field dark matter halos. We first calculate the event horizons and derive the equations of motion and effective potential in black hole geometries with different dark matter halos. We then compute the specific energy, specific angular momentum, and angular velocity of particles moving along circular orbits. We also derive the effective potentials to find the locations of the innermost stable circular orbit (ISCO) and compare them to the Schwarzschild and Kerr black holes without the dark matter halos. We also use the observed ISCO of the supermassive black hole at the Galactic Center of the Milky Way, Sagittarius A*, to constrain the dark matter halos.

Millisecond pulsars are extremely precise celestial clocks: as they rotate, the beamed radio waves emitted along the axis of their magnetic field can be detected with radio telescopes, which allows for tracking subtle changes in the pulsars’ rotation periods. A possible effect on the period of a pulsar is given by a potential coupling to dark matter, in cases where it is modeled with an “ultralight” scalar field. In this paper, we consider a universal conformal coupling of the dark matter scalar to gravity, which in turn mediates an effective coupling between pulsars and dark matter. If the dark matter scalar field is changing in time, as expected in the Milky Way, this effective coupling produces a periodic modulation of the pulsar rotational frequency. By studying the time series of observed radio pulses collected by the European Pulsar Timing Array experiment, we present constraints on the coupling of dark matter, improving on existing bounds. These bounds can also be regarded as constraints on the parameters of scalar-tensor theories of the Fierz-Jordan-Brans-Dicke and Damour-Esposito-Farèse types in the presence of a (light) mass potential term.

We present the deepest search to date for continuous gravitational waves from the neutron star in the Cassiopeia A (Cas A) supernova remnant, using the full LIGO dataset from the LIGO-Virgo-KAGRA (LVK) third observing run (O3). We use the weave semicoherent method with a first-stage coherence time of 30 days while restricting the search band to 20–200 Hz for assumed source ages greater than 300 years, substantially improving upon the sensitivity of a previous weave-based search for this source. No gravitational wave signal is detected. Estimates from simulated continuous wave signals indicate we achieve the most sensitive results to date across the explored parameter space volume, probing to a median strain magnitude as low as $4\times {10}^{-26}$ for frequencies near 200 Hz at 95% confidence level. The method presented here provides a template for future searches for Cas A and other central compact objects of interest using data from the ongoing fourth LVK run (O4).

The mixing between the chiral condensate and the density in hot and dense quantum chromodynamics (QCD) matter is familiar. We show that the mixing relevant for the ground state is considerably more extensive, and in particular also involves gluonic degrees of freedom. As a result, the Hessian of the QCD effective action is non-Hermitian, but retains a symmetry under combined charge and complex conjugation. This can lead to complex-conjugate pairs of eigenvalues of this Hessian, signaling regimes with spatially modulated correlations. Furthermore, based on the analytic structure of the quark determinant at a chiral critical point, we demonstrate that the corresponding massless critical mode is composed of the chiral condensate, the density and the Polyakov loops. Due to an avoided crossing, the critical mode turns out to be disconnected from the chiral condensate in vacuum. We present general arguments for all these features and illustrate them through explicit model calculations.

We derive the equations of motion for all the irreducible moments of the single-particle distribution function. We find that these moment equations of motion are highly coupled, with the dynamics of lower-rank moments always being coupled to those of a higher-rank, leading to an endless tower of equations. Considering a massless gas in Bjorken flow, we investigate how this hierarchy of differential equations can be properly truncated and solved.

We study the thermodynamic properties of a rigidly rotating relativistic Bose gas. First, we derive the solution of the equation of motion corresponding to a rotating complex Klein-Gordon field and determine the free propagator of this model utilizing the Fock-Schwinger proper-time method. Using this propagator, we then obtain the thermodynamic potential of this model in the zeroth and first perturbative level. In addition, we compute the nonperturbative ring contribution to this potential. Our focus is on the dependence of these expressions on the angular velocity, which effectively acts as a chemical potential. Using this thermodynamic potential, we calculate several quantities, including the pressure, angular momentum and entropy densities, heat capacity, speed of sound, and moment of inertia of this rigidly rotating Bose gas as functions of temperature ($T$), angular velocity ($\mathrm{\Omega }$), and the coupling constant ($\alpha$). We show that certain thermodynamic instabilities appear at high temperatures and large couplings. They are manifested as zero and negative values of the above quantities, particularly the moment of inertia and heat capacity. Zero moment of inertia leads to the phenomenon of supervorticity at certain $T$ or $\alpha$. Supervortical temperatures (couplings) decrease with increasing coupling (temperature). We also observe superluminal sound velocities at high $T$ and for large $\alpha$.