The first calculation of the response of the momentum space quark propagator to center vortices in the ground state fields of QCD is presented. Center vortices are identified on $2+1$-flavor dynamical gauge fields with $m_{\pi }\simeq 156\mathrm{MeV}$ to obtain the vortex-removed and vortex-only quark propagator. Dynamical mass generation is found to vanish upon vortex removal, while the vortex-only field is able to generate dynamical mass. These new signatures strengthen the lattice QCD evidence indicating that center vortices underpin both dynamical chiral symmetry breaking and quark confinement.

We explored the impact of fluctuations on anti–de Sitter black holes in higher dimensions, focusing on their effects on the thermodynamic properties and null trajectories of the black holes. Our findings indicate that mass oscillations lead to the perturbation of the event horizon location, thereby altering the Hawking temperature and Bekenstein-Hawking entropy. Furthermore, we derived equations for perturbed null rays near the horizon with arbitrary dimensions and obtained an analytical solution in the large $D$ limit.

We initiate the study of the information paradox of rotating Kerr black holes by employing the recently proposed island rule. It is known that the scalar field theory near the Kerr black hole horizon can be reduced to the two-dimensional effective theory. Working within the framework of the two-dimensional effective theory and assuming the small angular momentum limit, we demonstrate that the entanglement entropy of Hawking radiation from the nonextremal Kerr black hole follows the Page curve and saturates the Bekenstein-Hawking entropy at late times. In addition, we also discuss the effect of the black hole rotation on the Page time and scrambling time. For the extreme Kerr black hole, the entanglement entropy at late times also approximates the Bekenstein-Hawking entropy of the extreme Kerr black hole. These results imply that entanglement islands can provide a semiclassical resolution of the information paradox for rotating Kerr black holes.

One provides the exact expressions of the $(\beta ,\gamma ,\delta )$ post-Newtonian (PN) parameters in terms of the total energy and pressure integrals of a static spherical star, acting as the source of the gravitational field in Bergmann-Wagoner-Nordtvedt scalar-tensor gravity. This fixes the 2PN behavior of remote light rays in terms of the source’s internal structure, which constrains the latter from the former. The method can be extended to provide all the PN parameters, allowing to also fix the 2PN motion of massive test particles if needed. The exact $\beta$ and $\delta$ Brans-Dicke expressions recently obtained [Chauvineau and Nguyen, Phys. Lett. B 855, 138803 (2024); Nguyen and Chauvineau, Eur. Phys. J. C 84, 710 (2024).] are recovered in the constant $\omega$ case. As for the latter case, the scalar-tensor theory just involves one specific combination of the energy and pressures integrals, but some of these integrals explicitly involve the $\omega (\mathrm{\Phi })$ PN function. The increasing precision of spatial experiments, the urge to improve the gravitational phenomenology and the growing importance of compact stars in observational astronomy make obvious the interest of such direct links between PN parameters and stellar internal structure models.

We find some exact solutions for constant-density and quark matter equations of state in stellar structure models framed within the $f(R,T)=R+\lambda {\kappa }^{2}T$ theory of gravity, where $R$ is the curvature scalar, $T$ the trace of the stress-energy tensor, and $\lambda$ some constant. These solutions correspond to specific values of the constant $\lambda$ and represent different compactness states of the corresponding stars, though only those made of quark matter can be regarded as physical. The latter modify the compactness (Buchdahl) limit of neutron stars upward for $\lambda >0$ until saturating the one of black holes. Our results show that it is possible to find useful insights on stellar structure in this class of theories, a fact that could be used for obtaining constraints on limiting masses such as the minimum hydrogen burning mass.

In the Einstein-Maxwell theory with nonlinear electrodynamics (NED) fields, the singularity problem in general relativity is potentially resolved, leading to regular black hole solutions. In NED theories, photons follow null geodesics of an effective geometry that differs from the spacetime geometry itself. This raises an important question: Do NED fields produce unique observational signatures in the electromagnetic spectrum that can test regular black holes and NED theories? We analyze the shadows of two NED-charged regular black holes and their horizonless ultracompact objects (HUCOs) under two accretion models, comparing them with Schwarzschild black holes, focusing on shadow size, central brightness depression, and photon ring characteristics. Our results identify distinctive NED signatures that could be observable by the EHT, providing empirical evidence of NED fields and potentially ruling out previously considered viable candidates for astrophysical black holes models based on shadow measurements. Notably, NED-charged HUCOs generally exhibit only one unstable photon ring, thus avoiding the dynamical instability associated with stable photon rings and challenging the idea that objects with photon rings must be black holes.

Trace-free Einstein gravity is a prominent alternative to general relativity, which has two versions: one in which the energy-momentum conservation is assumed a priori and another in which it is not. In the first version, the cosmological constant arises as an integration constant. We report two diffeomorphism-invariant actions for trace-free Einstein gravity in which the energy-momentum conservation emerges directly from the equations of motion. The first action is based on the metric, while the second action is based on the tetrad and connection where the conservation of the energy-momentum holds if torsion vanishes. To achieve this, auxiliary fields but otherwise dynamical are introduced in the corresponding actions, which have the form of a constrained bigravity theory. These results constitute a significant advance in our understanding of trace-free Einstein gravity.

It has been suggested in recent literature that nonlinear and/or gravitomagnetic general relativistic effects can play a leading role in galactic dynamics, partially or totally replacing dark matter. Using the $1+3$ “quasi-Maxwell” formalism, we show, on general grounds, such hypothesis to be impossible.

In order to study the validity of analytical formulas used in the calculation of characteristic physical quantities related to vacuum bubbles, we conduct several numerical simulations of bubble kinematics in the context of cosmological first-order phase transitions to determine potentially existing systematic uncertainties. By comparing with the analytical results, we obtain the following observations: (1) The simulated false vacuum fraction will approach the theoretical one with increasing simulated volume. When the side length of the cubic simulation volume becomes larger than $14.5{\beta }_{\mathrm{th}}^{-1}$, the simulated results do not change significantly. (2) The theoretical expected total number of bubbles do not agree with the simulated ones, which may be caused by the inconsistent use of the false vacuum fraction formula. (3) The different nucleation rate prefactors do not affect the bubble kinetics much. (4) The lifetime distribution in the sound shell model does not obey an exponential distribution, in such a way as to cause a suppression in the gravitational wave spectra.

We extend the earlier linear studies of cosmological peculiar velocities to Friedmann universes with nonzero spatial curvature. In the process, we also compare our results with those obtained in cosmologies with Euclidean spatial sections. Employing relativistic cosmological perturbation theory, we first provide the differential formulas governing the evolution of peculiar velocities on all Friedmann backgrounds. The technical complexities of the curved models, however, mean that analytic solutions are possible only in special, though characteristic, moments in the lifetime of these universes. Nevertheless, our solutions exhibit persistent patterns that make us confident enough to generalize them. Thus, we confirm earlier claims that, compared to the Newtonian and the quasi-Newtonian studies, the relativistic analysis supports considerably stronger linear growth rates for peculiar-velocity perturbations. This result holds irrespective of the background curvature. Moreover, for positive curvature, the peculiar growth rate is found to be faster than that obtained in a spatially flat Friedman universe. In contrast, linear peculiar velocities appear to grow at a slower pace when their Friedmann host is spatially open. Extrapolating them to the present, our results seem to suggest faster bulk peculiar motions in overdense, rather than in underdense, regions of the Universe.

In this paper we present a framework in which the relational description of general relativity can be used to smoothly continue cosmological dynamical systems through the big bang without invoking quantum gravity effects. Cosmological spacetimes contain as a key dynamical variable a notion of scale through the volume factor $\nu$. However, no cosmological observer is ever able to separate their measuring apparatus from the system they are measuring, in that sense every measurement is a relative one, and measurable dynamical variables are, in fact, dimensionless ratios. This is manifest in the identification of a scaling symmetry or “dynamical similarity” in the Einstein-Hilbert action associated with the volume factor. By quotienting out this scaling symmetry, we form a relational system defined on a contact manifold whose dynamical variables are decoupled from scale. When the phase space is reduced to shape space, we show that there exists unique solutions to the equations of motion that pass smoothly through the initial cosmological singularity in flat Friedmann-Lemaître-Robertson-Walker, Bianchi I, and Quiescent Bianchi IX cosmologies.

Perturbative, or effective field theory (EFT)-based, full-shape analyses of galaxy clustering data involve “nuisance parameters” to capture various observational effects such as the galaxy-dark matter connection (galaxy bias). We present an efficient approach to set informative physically motivated priors on these parameters. We extract these priors from simulated galaxy catalogs based on halo occupation distribution (HOD) models. First, we build a joint distribution between EFT galaxy bias and HOD parameters from a set of 10,500 HOD mock catalogs. We use the field level EFT technique that allows for cosmic variance cancellation, enabling a precision calibration of EFT parameters from computationally inexpensive small-volume simulations. Second, we use neural density estimators—normalizing flows—to model the marginal probability density of the EFT parameters, which can be used as a prior distribution in full shape analyses. As a first application, we use our HOD-based priors in a new analysis of galaxy power spectra and bispectra from the BOSS survey in the context of single field primordial non-Gaussianity. We find that our priors lead to a reduction of the posterior volume of bias parameters by an order of magnitude. We also find $f_{\mathrm{NL}}^{\text{equil}}=320\pm 300$ and $f_{\mathrm{NL}}^{\text{ortho}}=100\pm 130$ (at 68% CL) in a combined two-template analysis, representing a $\approx 40\%$ improvement in constraints on single field primordial non-Gaussianity, equivalent to doubling the survey volume.

The mimetic gravity theory is one of the interesting modified gravity theories, which aims to unify the matter component of our universe within the power of gravity. The mimetic-like theory can also be responsible for primordial perturbations production, e.g., when the mimetic field is set to be like a curvaton field, and the adiabatic perturbation can thus be generated from the isocurvature perturbation via usual curvaton mechanism [Zhang, Liu, and Qiu, Phys. Rev. D 107, 043510 (2023)]. In the original mimetic curvaton model, the parameter $\lambda$ was purely an algebraic multiplier, lack of any perturbed dynamics. In the current paper, we treat $\lambda$ as an auxiliary field, with its perturbation $\delta \lambda$ evolving alongside. We show that, with such a consideration, the adiabatic perturbation can still be generated from the curvaton mechanism, and becomes scale invariant with different field space configurations.

Departing from standard slow-roll conditions is one way of putting the inflationary paradigm to test, and constraining the dynamics of the inflaton field with a constant rate of roll of the inflaton field, also known as the constant-roll scenario, is one way of exploring such deviation from the standard slow-roll dynamics. In this manuscript, we explore such a possibility in a variant inflationary scenario, known as warm inflation (WI). We construct and derive the conditions for having constant-roll WI models where inflation lasts at least for 60 $e$-folds, gracefully exits the constant-roll inflation phase, and maintains near thermal equilibrium of the system, which is an essential feature of WI in the slow-roll regime. We show that, while certain models of WI (the ones with dissipative coefficient as a function of temperature alone) can accommodate constant-roll dynamics, others (with dissipative coefficient as a function of temperature and the inflaton field both) fail to maintain thermal equilibrium once the constant-roll condition is imposed and hence cannot produce a constant-roll WI phase.

We have developed a set of four fully coupled Boltzmann equations to precisely determine the relic density and temperature of dark matter by including three distinct sectors: dark matter, light scalar, and standard model sectors. The intricacies of heat transfer between dark matter (DM) and the standard model sector through a light scalar particle are explored, inspired by stringent experimental constraints on the scalar-Higgs mixing angle and the DM-scalar coupling. Three distinct sectors emerge prior to DM freeze-out, requiring fully coupled Boltzmann equations to accurately compute relic density. Investigation of forbidden, resonance, and secluded DM scenarios demonstrates significant deviations between established methods and the novel approach with fully coupled Boltzmann equations. Despite increased computational demands, this emphasizes the need for improved precision in relic density calculations, underlining the importance of incorporating these equations in comprehensive analyses.

We investigate the initiation of cosmic inflation, in full numerical relativity, from preinflationary scenarios with large tensor and vector fluctuations in the metric. These settings are characterized by having large values in the Weyl curvature tensor. In the matter sector, we consider a single scalar field with inhomogeneous field velocities, corresponding to a kination period. In the context of large-field inflation, it is shown that the onset of inflation continues to be robust to this type of initial conditions, and that during inflation the Universe successfully homogenizes and flattens any type of curvature, leading to a Friedmann-Lemaître-Robertson-Walker Universe after just a few tens of $e$-folds of accelerating expansion.

Laser frequency noise suppression is a critical requirement for the Laser Interferometer Space Antenna (LISA) mission to detect gravitational waves. The baseline laser stabilization is achieved using cavity prestabilization and a postprocessing technique called Time-Delay Interferometry (TDI). To enhance the margins for TDI, alternate laser-locking schemes should be investigated. A novel stabilization blending the excellent stability of the arm with the existing cavity reference has been shown theoretically to meet the first-generation TDI margins. This locking system was designed to be implemented as a firmware change and have minimal or no changes to the LISA hardware. This paper experimentally verifies the hybrid laser-locking technique by utilizing two references—an optical cavity and an interferometer with delay imparted using 10 km of optical fiber. The results indicate the viability of the combination of the arm-cavity-locking system for LISA. They show the key benefits envisioned by this technique: suppression of the cavity fluctuations by the arm sensor (by 21 dB in this demonstration) and reduction of Doppler pulling of the laser frequency, a key technical challenge for arm locking.

We present a novel machine learning framework tailored to detect massive black hole binaries observed by spaceborne gravitational wave detectors like the Laser Interferometer Space Antenna (LISA) and predict their future merger times. The detection is performed via convolutional neural networks that analyze time-evolving time-delay interferometry (TDI) spectrograms and utilize variations in signal power to trigger alerts. The prediction of future merger times is accomplished with reinforcement learning. Here, the proposed algorithm dynamically refines time-to-merger predictions by assimilating new data as it becomes available. Deep Q-learning serves as the core technique of the approach, utilizing a neural network to estimate Q-values throughout the observational state space. To enhance robust learning in a noisy environment, we integrate an actor-critic mechanism that segregates action proposals from their evaluation, thus harnessing the advantages of policy-based and value-based learning paradigms. We leverage merger estimation obtained via template matching with truncated waveforms to generate rewards for the reinforcement learning agent. These estimations come with inherent uncertainties, which magnify as the merger event stretches further into the future. The reinforcement learning setup is shown to adapt to these uncertainties by employing a dedicated policy fine-tuning approach, ensuring the reliability of predictions despite the varying degrees of template-matching precision. The algorithm denotes a first step toward a low-latency model that provides early warnings for impending transient phenomena. By delivering timely and accurate forecasts of merger events, the framework supports the coordination of gravitational wave observations with accompanied electromagnetic counterparts, thus enhancing the prospects of multimessenger astronomy. We use the LISA Spritz data challenge for validation.

The helicity correlation of two back-to-back hadrons is a powerful tool that makes it possible to probe the longitudinal spin transfer $G_{1L}$ in unpolarized hadronic collisions. In this work, we investigate the helicity correlation of back-to-back dihadrons produced in photon-nucleus collisions with both spacelike and quasireal photons and explore its potential in understanding the flavor dependence of spin-dependent fragmentation functions. We present helicity amplitudes of partonic scatterings with both virtual and real photons and make numerical predictions for the dihadron helicity correlations at the future Electron Ion Collider experiment and the current Relativistic Heavy Ion Collider/LHC ultraperipheral collision experiment. Future experimental measurements can also illuminate the fragmentation function of circularly polarized gluons.