We investigate the $1+1+2$ covariant formalism in the presence of nonmetricity. Focusing on locally rotationally symmetric spacetimes, we show how nonmetricity affects all the kinematic quantities involved in the covariant $1+1+2$ decomposition. We apply the resulting geometrical framework to study both homogeneous solutions and static spherically symmetric solutions in the context of $f(\mathcal{Q})$ gravity. We obtain sufficient conditions for homogeneous solutions with flat spatial hypersurfaces and Schwarzschild-de Sitter type solutions in the $1+1+2$ formalism. We also explore an elementary gravastar solution utilizing covariant junction conditions.

We study the class of six-dimensional $\mathrm{\Lambda }$-vacuum spacetimes which admit a nondegenerate multiple Weyl aligned null direction $\mathit{\ell }$ (thus being of Weyl type II or more special) with a “generic” optical matrix. Subject to an additional assumption on the asymptotic falloff of the Weyl tensor, we obtain the most general metric of this class, which is specified by one discrete (normalized) and three continuous parameters. All solutions turn out to be Kerr-Schild spacetimes of type D and, in passing, we comment on their Kerr-Schild double copy. We further show that the obtained family is locally isometric to the general doubly spinning Kerr-NUT-(A)dS metric with the NUTs parameters switched off. In particular, the Kerr-(A)dS subclass and its extensions (i.e., analytic continuation and “infinite-rotation” limit) are recovered when certain polynomial metric functions are assumed to be fully factorized. As a side result, a unified metric form which encompasses all three branches of the extended Kerr-(A)dS family in all even dimensions is presented in an appendix.

The ringdown of perturbed black holes has been studied since the 1970s, but until recently, studies have focused on linear perturbations. There is now burgeoning interest in nonlinear perturbative effects during ringdown. Here, using a hyperboloidal framework, we provide a complete treatment of linear and quadratic quasinormal modes (QNMs and QQNMs) in second-order perturbation theory, in Schwarzschild spacetime. We include novel methods for extracting QNMs and QQNMs amplitudes using a Laplace transform treatment, allowing for the inclusion of arbitrary initial data. We produce both time- and frequency-domain codes. From these codes, we present new results further exploring the unforeseen dependence of QQNMs amplitudes on the parity of the progenitor system, as demonstrated in our letter [Phys. Rev. Lett. 134, 061401 (2025).]. Our numerical results are restricted to perturbations of a Schwarzschild black hole, but our methods extend straightforwardly to the astrophysically realistic case of a Kerr black hole.

We obtain the generalized quasi-Keplerian parametrization for compact binaries on quasihyperbolic orbits at second post-Newtonian (2PN) order in a class of massless scalar-tensor theories, extending the analogous results for quasielliptic systems [Phys. Rev. D 109, 104003 (2024)]. In particular, we compute the conservative scattering angle and impact parameter at 2PN. Our results are consistent with the 2PN conservative scatter-to-bound map in these theories between the scattering angle and the periastron advance. We then compute the total energy and angular momentum lost by the system and study the limiting cases of parabolic orbits and bremsstrahlung, including a re-expansion of our results at seventh post-Minkowskian order. Flux-balance arguments then allow us to compute the dissipative contributions to the scattering angle at 1.5PN and 2.5PN, completing the full scattering angle at 2.5PN in these theories. Finally, we obtain, in general relativity, an expression for the 3PN impact parameter in the conservative sector, correcting previous literature.

Numerical relativity waveforms are a critical resource in the quest to deepen our understanding of the dynamics of, and gravitational waves emitted from, merging binary systems. We present 181 new numerical relativity simulations as the second MAYA catalog of binary black hole waveforms (a sequel to the Georgia Tech waveform catalog). Most importantly, these include 55 high mass ratio ($q>=4$), 48 precessing, and 92 eccentric ($e>0.01$) simulations, including 7 simulations that are both eccentric and precessing. With these significant additions, this new catalog fills in considerable gaps in existing public numerical relativity waveform catalogs. The waveforms presented in this catalog are shown to be convergent and are consistent with current gravitational-wave models.

A promising way to test the physics of the accelerated expansion of the Universe is by studying the growth rate of matter fluctuations, which can be parametrized by the matter energy density parameter to the power $\gamma$, the so-called growth index. It is well known that the $\mathrm{\Lambda }\mathrm{CDM}$ cosmology predicts $\gamma =0.55$. However, using observational data, Nguyen et al. [Evidence for suppression of structure growth in the concordance cosmological model, Phys. Rev. Lett. 131, 111001 (2023)] measured a much higher $\gamma =0.633_{-0.024}^{+0.025}$, excluding the $\mathrm{\Lambda }\mathrm{CDM}$ value within $3.7\sigma$. In this work, we analyze whether dark energy (DE) with the equation-of-state parameter described by the Chevallier-Polarski-Linder (CPL) parametrization can significantly modify $\gamma$ with respect to the predicted $\mathrm{\Lambda }\mathrm{CDM}$ one. In addition to the usual smooth DE (SDE) scenario, where DE perturbations are neglected on small scales, we also consider the case of clustering dark energy (CDE), which has more potential to impact the growth of matter perturbations. In order to minimally constrain the background evolution and assess the largest meaningful $\gamma$ distribution, we use data from 32 cosmic chronometers, $H(z)$, data points. In this context, we found that both SDE and CDE models described by the CPL parametrization have almost negligible probability of providing $\gamma >0.6$. However, given that the measured $\gamma$ value assumes the $\mathrm{\Lambda }\mathrm{CDM}$ background, a direct statistical measure of the incompatibility between theory and the measured value cannot be done for other backgrounds. Thus, we devise a method in order to make a quick estimation of the $\gamma$ constraints for CPL background. This method indicates that, when using Dark Energy Spectroscopic Instrument data release 2 baryon acoustic oscillation data to constrain background parameters, no significant changes in the $\gamma$ central value and uncertainty is observed. Consequently, both SDE and CDE described by CPL parametrization shall have a comparable level of tension with the expected $\gamma$ measurements. Moreover, we present new fitting functions for $\gamma$, which are more accurate and general than the one proposed by Linder [Cosmic growth history and expansion history, Phys. Rev. D 72, 043529 (2005)] for SDE and, for the first time, fitting functions for CDE models.

Astrophysical foreground substraction is crucial to retrieve the cosmic microwave background (CMB) polarization out of the observed data. Recent efforts by Leloup et al. and Morshed et al. have been carried out toward the development of a minimally informed component separation method to handle a priori unknown foreground spectral energy distributions (SEDs), while being able to estimate cosmological, foreground, and potentially instrumental parameters, jointly. In this paper, we develop a semianalytical performance forecasting framework for the minimally informed method and we validate it by comparing its results against direct sampling of the harmonic-based likelihood and the pixel domain implementation micmac. We then use the forecasting tool to demonstrate the robustness of the bias correction procedure introduced in the minimally informed approach. We find that a data-driven approach based on the currently available observational data is enough to efficiently regularize the bias of the method.

Preheating at the end of inflation is a violent nonlinear process that efficiently transfers the energy of the inflaton to a second field, the preheat field. When the preheat field is light during inflation and its background value modulates the preheating process, the superhorizon isocurvature perturbations of the preheat field may be converted to curvature perturbations that leave an imprint on the cosmic microwave background and the large-scale structure of the Universe. We use linear-perturbation theory on cosmological scales and high-precision lattice simulations in postinflation Hubble patches to study kinetic preheating after $\alpha$-attractor inflation, a case where the effective mass of the preheat field is naturally suppressed during inflation. By comparing the expansion e-folds between different Hubble patches, we find that the conversion from isocurvature perturbations to curvature perturbations is very inefficient and can hardly be detected by cosmological observations.

We describe the implementation of a new approach to the numerical evaluation of the effects of noncold relics on the evolution of cosmological perturbations. The Boltzmann hierarchies used to compute the contributions of these relics to the stress-energy tensor are replaced with a set of integral equations. These integral equations take the form of convolutions and are solved iteratively with the rest of the system. We develop efficient algorithms for evaluating these convolutions using nonuniform fast Fourier transforms (NUFFTs). This approach enables efficient and accurate evaluation of the cosmic microwave background anisotropies and matter power spectra, all the way through the history of the Universe, without relying on semianalytic approximations at late times. We implement this method in the Boltzmann solver class, resulting in a new code called classier (for class Integral Equation Revision), and apply it to massive-neutrino perturbations as a demonstration. The implementation is optimized to accurately capture the distinct behaviors of perturbations in both super-/near-horizon and subhorizon regimes. Our results match the accuracy of a fully converged Boltzmann hierarchy solution while avoiding numerical artifacts from truncation of the Boltzmann hierarchy at finite multipole and offering substantial speedups depending on the required precision and the range of scales of interest. This new framework provides a practical and robust alternative for the truncated Boltzmann hierarchy approach, especially for studying beyond $\mathrm{\Lambda }\mathrm{CDM}$ noncold relics with signatures on small scales. classier is publicly available.

Large-scale (i.e., $\gtrsim \mathrm{kpc}$) and micro-Gauss-scale magnetic fields have been observed throughout the Milky Way and nearby galaxies. These fields depend on the geometry and matter-energy composition, can display complicated behavior such as direction reversals, and are intimately related to the evolution of the source galaxy. Simultaneously, gravitational-wave astronomy offers a new probe into astrophysical systems; for example, the Laser Interferometer Space Antenna (LISA) will observe the mergers of massive (i.e., $M>{10}^6{M}_{\odot }$) black-hole binaries and provide extraordinary constraints on the evolution of their galactic hosts. In this work, we show how galactic, large-scale magnetic fields and their electromagnetic signatures are connected with LISA gravitational-wave observations via their common dependence on the massive black-hole binary formation scenario of hierarchical galaxy mergers. Combining existing codes, we astrophysically evolve a population of massive binaries from formation to merger and find that they are detectable by LISA with signal-to-noise ratio $\sim {10}^3$ which is correlated with quantities from the progenitors’ phase of circumbinary disk migration such as the maximum magnetic field magnitude $|\mathbf{B}|\approx 7\mathrm{\mu }\mathrm{G}$, polarized intensity, and Faraday rotation measure. Interesting correlations result between these observables arising from their dependencies on the black-hole binary total mass, suggesting a need for further analyses of the full parameter space. We conclude with a discussion on this new multimessenger window into galactic magnetic fields.

Strong magnetic fields make neutron stars potential sources of detectable electromagnetic and gravitational-wave signals. Hence, inferring these magnetic fields is critical to understand the emissions of neutron stars. However, due to the lack of direct observational evidence, the interior magnetic field configuration remains ambiguous. Here, for the first time, we show that the internal magnetic field strength along with the composition of a neutron star can be directly constrained by detecting the gravitational waves from the phase-transition-induced collapse of a magnetized neutron star. By dynamically simulating this collapsing event, we first find that the dominant peaks in the gravitational waveform are the fundamental $l=0$ quasiradial $F$ mode and the fundamental $l=2$ quadrupolar ${}^{2}f$ mode. We next show that the maximum gravitational wave amplitude $|h{|}_{\max }$ increases with the maximum magnetic field strength of the interior toroidal field ${\mathcal{B}}_{\max }$ until the maximum rest-mass density at bounce ${\rho }_{\max ,\mathrm{b}}$ decreases due to the increasing ${\mathcal{B}}_{\max }$. We then demonstrated that the magnetic suppression of fundamental modes found in our previous work remains valid for the hybrid stars formed after the phase-transition-induced collapses. We finally show that measuring the frequency ratio between the two fundamental modes $f_{{}^{2}f}/f_F$ allows one to infer ${\mathcal{B}}_{\max }$ and the baryonic mass fraction of matter in the mixed phase $M_{\mathrm{mp}}/M_0$ of the resulting hybrid star. Consequently, taking ${\mathcal{B}}_{\max }$ and $M_{\mathrm{mp}}/M_0$ as examples, this work has demonstrated that much information inside neutron stars could be extracted similarly through measuring the oscillation modes of the stars.

Rotating black holes with strong magnetic fields leads to an outward energy flux in the form of jets governed by the Blandford-Znajek mechanism. These jets depend on factors such as accretion rate, magnetic flux, and the spin of the black hole. When such rotating black holes get attached to a cosmic string, it leads to a further rotational energy extraction, leading to a reduced spin. We consider such a system and investigate the effect this reduced spin has on the jet power and its dependence on the cosmic string tension, $\mu$. It is shown that for a constant magnetic flux and accretion rate, the jet energy flux is inversely proportional to ${\mu }^2$. Interestingly, the rate of this energy flux varies with time and is again dependent on $\mu$. We also study the total angular momentum evolution of the black hole by considering four major effects: accretion, jets, cosmic string energy extraction, and the Bardeen-Petterson effect. Further, we attempt to analyze the condition for the spin-down of a black hole due to these effects and find out that it is possible for both small and large string tensions, with a higher possibility for larger string tensions. Another interesting phenomenon that has been proposed is the alignment of the jet with the cosmic string. Additionally, the Bardeen-Petterson effect also leads to alignment or misalignment of the inner and outer disks depending on the alignment of the string. In this manuscript we propose that these results might have an observable effect and hence could serve as a potential detection method for cosmic strings.

The nature of dark matter is still mysterious despite various astronomical evidence. As a possible candidate, self-interacting dark matter (SIDM) can potentially resolve some issues appearing in the cold dark matter paradigm. Here we investigate how SIDM around supermassive black holes (SMBHs) in galaxy centers may form a density spike and imprint in the spectrum shape of stochastic gravitational-wave background from SMBH binaries (SMBHBs). Employing a refined dynamical friction formula and consistently evolving the orbital dynamics, we demonstrate that current pulsar timing array (PTA) data are sensitive to the cross section of SIDM with $\sigma (v)/m_{\chi }\lesssim 0.66{\mathrm{cm}}^2/\mathrm{g}$, comparable to other astrophysical probes. We also highlight the importance of including the eccentricity of SMBHBs in the parameter inference, which would affect the results significantly. Our findings reveal the promising potential of PTA observations in probing the nature of dark matter.

The elastic properties of the neutron star crust are thought to play a crucial role in various phenomena of neutron stars (glitches, oscillations, and gravitational wave emission) and should be described quantitatively to model these phenomena. The fundamental problem of this description is associated with the polycrystalline nature of the crust: similar to terrestrial materials, the elastic moduli, strictly speaking, depend on the shape and orientation of crystallites, but for the crust, they are unknown. As a result, some assumptions are generally required to predict the elastic properties or constrain their possible range. In this paper, we follow the commonly believed assumption that the crust is (locally) isotropic, which allows us to describe elastic properties by two (effective) parameters: bulk and shear moduli. The bulk modulus is well determined by the Voigt-Reuss bounds, and we constrain the shear modulus by applying, for the first time in astrophysics of compact stars, the variational Hashin-Shtrikman approach, based on the additional assumption that there are no correlations in the orientation of crystallites. We analyze the Hashin-Shtrikman bounds for the one-component crust, taking into account the electron screening and the motion of the nuclei, and for two-component static crystals. In particular, we demonstrate that within applied assumptions the effective shear modulus should be lower than the Voigt estimate, typically applied in the astrophysical literature.

Domain wall fermions use a $2n$-dimensional spacetime defect embedded in ($2n+1$)-dimensional spacetime to realize massless lattice Dirac fermions. Recent work has extended this idea to realize a single unpaired Weyl fermion in a finite lattice. Here, we realize the same using a $2n$-dimensional string defect embedded in ($2n+2$)-dimensional spacetime on a finite lattice for $n=1$. This string is a lattice version of the continuum axion string described in Callan-Harvey [Nucl. Phys. B250, 427 (1985)]. Our results are obtained in a Hamiltonian formulation in Minkowski spacetime. Extending the results to Euclidean spacetime and to $n>1$ is straightforward. This work has applications to lattice chiral gauge theories and axion cosmology.

Heavy-ion collision experiments such as the Large Hadron Collider and the Relativistic Heavy Ion Collider offer a unique platform to study several key properties of the quark-gluon plasma (QGP), a deconfined state of strongly interacting matter. Quarks, being the electrically charged particles, can induce an electric current in the medium in response to the temperature gradients. Hence, the QGP medium can behave like a thermoelectric medium. The thermoelectric coefficients, such as the Seebeck and Thomson coefficients, can help us to understand the intricate transport phenomenon of the medium. In peripheral collisions, the intense, transient, and time-dependent magnetic field created due to spectator protons significantly influences the thermoelectric properties of the QGP medium, affecting the charge and heat transport. This work uses the quasiparticle model to calculate the Thomson coefficient in QGP. The Thomson effect, describing the continuous heating or cooling of the charge-carrying medium in the presence of temperature gradients, remains largely unexplored in QGP. The Seebeck effect, which relates temperature gradients to induced electric fields, has been widely studied in the literature. For the first time, we calculate the magneto-Thomson and transverse Thomson coefficients. We have studied their dependence on temperature, baryon chemical potential, center of mass energy, and time-dependent magnetic field with different decay parameters. The transverse Thomson effect originates due to the presence of the Nernst effect in the presence of a magnetic field. Our results provide new insights into the higher-order thermoelectric transport properties of the QGP medium in the context of heavy-ion collisions.

We bootstrap the leading-order hadronic contribution to $a_{\mu }$ using unitarity, analytic properties, crossing symmetry and finite energy sum rules (FESR) from QCD, establishing a lower bound. Combining this lower bound with the remaining precisely calculated contributions from quantum electrodynamics and electroweak interactions, we achieve a lower bound on muon anomaly $a_{\mu }$. Since the FESRs have uncertainties, our bound depends on the choices of FESRs within these uncertainties. A conservative choice of the FESR gives a conservative lower bound, consistent with Standard Model (SM) data-driven prediction. We show that there are other valid choices of FESRs within the uncertainties that lead to lower bounds, which are inconsistent with SM data-driven prediction but consistent with the measured values of the muon anomaly. The bootstrapped spectral density shows a $\rho$-resonance peak similar to experimental hadronic cross-ratio data, providing a bootstrap prediction for $\rho$-meson mass.

Recent computations of bottomonium correlation functions with extended sources in lattice-discretized quantum chromodynamics (lQCD) provide new insights into heavy-quark dynamics at distance scales which are of the order of the inverse temperature. We analyze these results employing the thermodynamic $T$-matrix framework, in a continued effort to interpret lQCD data for quarkonium correlation functions in a nonperturbative and self-consistently solved quantum-many-body approach to a strongly coupled quark-gluon plasma (QGP). Its key inputs are the in-medium driving kernel (potential) of the scattering equation and an interference function which implements 3-body effects in the quarkonium coupling to the thermal medium. A simultaneous description of lQCD results for the bottomonium correlators with extended operators and the previously analyzed Wilson line correlators only requires minor refinements of the potential but calls for stronger interference effects at larger separation of the bottom quark and antiquark. We then analyze the poles of the self-consistent $T$ matrices on the real axis to assess the survival of the various bound states. We estimate the pertinent temperatures where the poles disappear for the various bottomonium states and discuss the relation to the corresponding peaks in the bottomonium spectral functions. We also recalculate the spatial diffusion coefficient of the QGP and find it to be similar to that in our previous study.

We study, for the first time, the interplay between color-confining and chiral symmetry-breaking dynamics in gauge-fermion systems with a general number of flavors and colors. Specifically, we work out the flavor dependence of the confinement and chiral symmetry breaking scales. We connect the QCD-like regime, in quantitative agreement with lattice data, with the perturbative conformal limit, thereby exploring uncharted region of theory space. This analysis is done within the first-principles functional renormalization group approach to gauge-fermion systems and is facilitated by a novel approximation scheme introduced here. This novel scheme enables a relatively simple access to the confining dynamics. This allows us to investigate the whole landscape of many-flavor theories and to provide a cartography of their phase structure. In particular, we uncover a novel phase with the locking of confining and chiral dynamics at intermediate flavor numbers. We also explore the close-conformal region that displays a walking behavior. Finally, we provide a quantitative estimate for the lower boundary of the conformal Caswell-Banks-Zaks window, with a $N_f^{\mathrm{crit}}(N_c=3)=9.60_{-0.53}^{+0.55}$. This work offers a self-consistent framework for charting the landscape of strongly interacting gauge-fermion theories necessary to reliably study strongly coupled extensions of the Standard Model of particle physics.