We study the quantum dynamics of the Lemaître-Tolman-Bondi space-times using a polymer quantization prescription based on loop quantum cosmology that incorporates fundamental discreteness. By solving an effective equation derived from this quantization, we find analytical solutions for the Oppenheimer-Snyder and thin-shell collapse models, and numerical solutions for a variety of asymptotically flat collapsing dust profiles. Our study (i) tracks the formation, evolution, and disappearance of dynamical horizons, (ii) shows that matter undergoes a nonsingular bounce that results in an outgoing shock wave, (iii) determines black hole lifetime to be proportional to the square of its mass, and (iv) provides a conformal diagram that substantially modifies the standard “information loss” picture by resolving the singularity and replacing the event horizon by transient apparent horizons.

We introduce the cosmological analysis of the Dirac-Born-Infeld dRGT massive gravity theory which is a new extension of de Rham-Gabadadze-Tolley (dRGT) massive gravity. In this theory, we consider the Dirac-Born-Infeld (DBI) scalar field which is coupled to the graviton field. Moreover, we perform the cosmological background equations, and we demonstrate the self-accelerating background solutions. We show that the theory consists of self-accelerating solutions with an effective cosmological constant. In the following, we exhibit tensor perturbations analyses and achieve the dispersion relation of gravitational waves. We analyze the propagation of gravitational perturbation in the Friedmann-Lemaître-Robertson-Walker cosmology in the DBI dRGT massive gravity. Finally, we present the vector and scalar perturbations to show the stability conditions of the theory.

de Sitter space is an important maximally symmetric vacuum solution of Einstein’s field equation, located in a central place in cosmology in explaining the accelerated expansion of the Universe. Here in the view of optics, we propose the de Sitter space with a generalized Poincaré lens based on the equivalence between the static curved space-time and the isotropic optical medium. The correspondence of familiar de Sitter space and the Poincaré disk can be regarded as a special case therein. We also discover that the generalized de Sitter space has a topological cosmic string kernel in the center which can deflect light in different ways. This feature can be evidenced and visualized in its equivalent generalized Poincaré lens with a tunable horizon. To gain more intrinsic understanding, we further introduce its one-dimensional lens. Finally, for a possible application, we implement a multiple source illusion effect in the generalized Poincaré lens and find that the energy flow obeys the topological Poincaré-Hopf theorem. Our work is an attempt in the fruitful interplay between optics and general relativity and may enlighten other interesting relevant explorations.

Gravitational dark matter (DM) is the simplest possible scenario that has recently gained interest in the early Universe cosmology. In this scenario, DM is assumed to be produced from the scattering of inflatons through the gravitational interaction during reheating. Gravitational production from the radiation bath will be ignored as our analysis shows it to be suppressed for a wide range of reheating temperatures $(T_{\mathrm{re}})$. Ignoring any other internal parameters except the DM mass $(m_Y)$ and spin, a particular inflation model such as $\alpha$ attractor, with a specific scalar spectral index $(n_s)$ has been shown to uniquely fix the DM mass of the present Universe. For fermion type DM, we found the mass $m_f$ should be within $({10}^4–{10}^{13})\mathrm{GeV}$, and for boson/vector type DM, the mass $m_s/m_X$ turned out to be within $(1.2\times {10}^{-14}/9.6\times {10}^{-14}–{10}^{13})\mathrm{GeV}$. Interestingly, if the inflaton equation of state ${\omega }_{\varphi }\to 1/3$, the DM mass also approaches towards unique value, $m_f\sim {10}^{10}\mathrm{GeV}$ and $m_s(m_X)\sim {10}^3(8\times {10}^3)\mathrm{GeV}$. We further analyzed the phase space distribution $f_Y$ and free streaming length ${\lambda }_{\mathrm{fs}}$ of these gravitationally produced DM. $f_Y$, which is believed to encode important information about DM, contains a characteristic primary peak at the initial time where the gravitational production is maximum for both fermionic and bosonic DM. Apart from this fermionic phase space, the distribution function contains an additional peak near the inflaton and fermion mass equality ($m_Y\sim m_{\varphi }$) arising for ${\omega }_{\varphi }>5/9$. Furthermore, the height of this additional peak turned out to be increasing with decreasing $T_{\mathrm{re}}$ and at some point, dominates over the primary one. Since reheating is a causal process and DM is produced during this phase, gravitational instability forming small-scale DM structures during this period will encode those phase space information and be observed at present. The crucial condition of forming such a small-scale DM structure during reheating suggests that the ${\lambda }_{\mathrm{fs}}$ must be less than the length scale associated with the mode reentering the Hubble radius at the end of reheating ${\lambda }_{\mathrm{re}}$, which has been analyzed in detail. We further estimate in detail the range of scales within which the above condition will be satisfied for different masses of scalar, fermionic, and vector DM. Finally, we end by stating the fact that all our results are observed to be insensitive on the parameter $\alpha$ of the inflaton potential within the allowed range set by the latest Planck and BICEP/Keck results.

The majority of massive stars are found in close binaries which: (i) are prone to merge and (ii) are accompanied by another distant tertiary star (triples). Here, we study the evolution of the stellar postmerger binaries composed of the merger product and the tertiary companion. We find that postmerger binaries originating from compact stellar triples with outer semimajor axes $a_{\mathrm{out},\mathrm{init}}\lesssim {10}^1–{10}^2\mathrm{AU}$ provide a new way to form binary black hole mergers in the galactic field. By means of a population synthesis, we estimate their contribution to the total black hole merger rate to be $\mathcal{R}(z=0)=0.3–25.2{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$. Merging binary black holes that form from stellar postmerger binaries have exceptionally low mass ratios. We identify a critical mass ratio $q\simeq 0.5$ below which they dominate the total black hole merger rate in the field. We show that after including their additional contribution, the mass ratio distribution of binary black hole mergers in the galactic field scenario is in better agreement with that inferred from gravitational wave detections.

Magnetic fields are expected to play a key role in the dynamics and the ejection mechanisms that accompany the merger of two neutron stars. General relativistic magnetohydrodynamic (MHD) simulations offer a unique opportunity to unravel the details of the ongoing physical processes. Nevertheless, current numerical studies are severely limited by the fact that any affordable resolution remains insufficient to fully capture the small-scale dynamo, initially triggered by the Kelvin-Helmholtz instability, and later sourced by several MHD processes involving differential rotation. Here, we alleviate this limitation by using explicit large-eddy simulations, a technique where the unresolved dynamics occurring at the subgrid scales (SGS) is modeled by extra terms, which are functions of the resolved fields and their derivatives. The combination of high-order numerical schemes, high resolutions, and the gradient SGS model allow us to capture the small-scale dynamos produced during the binary neutron star mergers, as shown in previous works. Here, we follow the first 50 milliseconds after the merger and, for the first time, we find numerical convergence on the magnetic field amplification, in terms of integrated energy and spectral distribution over spatial scales. Among other results, we find that the average intensity of the magnetic field in the remnant saturates at $\sim {10}^{16}\mathrm{G}$ around 5 ms after the merger. After 20–30 ms, both toroidal and poloidal magnetic field components grow continuously, fed by the winding mechanism that provides a slow inverse cascade, i.e., gradually transferring kinetic into magnetic energy. We find no clear hints for magnetorotational instabilities and no significant impact of the magnetic field on the redistribution of angular momentum in the remnant in our simulations, probably due to the very turbulent and dynamical topology of the magnetic field at all stages, with small-scale components largely dominating over the large-scale ones. Although the magnetic field grows near the rotation axis of the remnant, longer large-eddy simulations are necessary to further investigate the formation of large-scale, helical structures close to the rotational axis, which could be associated to jet formation.

Space-based gravitational-wave detectors offer new prospects for probing the interior of white dwarfs in binary systems through the imprints of tidal effects on the gravitational-wave signal. Some of the binaries that will be observed could have evolved for long enough for the white dwarfs to be at least partially crystallized. The apsidal motion constant $k_2$ (also called the second gravitoelectric Love number) of a cold crystallized white dwarf is computed in full general relativity considering different compositions. The elasticity of the crystallized core is found to systematically reduce the tidal deformability, especially for low-mass stars. Fully relativistic results are compared to those obtained in Newtonian gravity. It is shown that the relativistic correction to the observable tidal deformability $k_2{R}^5$ (where $R$ is the stellar radius) is negligible for low-mass white dwarfs but becomes increasingly important for more massive white dwarfs. When approaching the maximum mass, the application of Newtonian theory instead of general relativity leads to dramatic errors. The case of eccentric binaries, for which the precession of the periastron causes a frequency splitting of the gravitational-wave signal depending on the apsidal motion constants of the two stars, is investigated. Future measurements of the precession rate by the Laser Interferometer Space Antenna, which is planned to be in operation within the next decade, could potentially provide estimates of the individual masses. It is found that the errors incurred by the neglect of the elasticity of the crystallized core could be very large, especially for low-mass white dwarfs. Gravitational-wave observations could thus provide a new way to study the crystallization of white dwarfs.

We investigate the magnetism of QCD matter and pion mass under magnetic fields, including the contribution from the tensor-type spin polarization (TSP) and the anomalous magnetic moment (AMM) of quarks. The AMM reduces the lowest Landau level (LLL) energy and the TSP lifts up the LLL energy; thus, the AMM and the TSP have opposite effects on the magnetized quark matter. It is found that the TSP enhances the magnetic catalysis of chiral condensate and induces diamagnetism (negative magnetic susceptibility) of quark matter at low temperature; both neutral and charged pion masses increase quickly with magnetic field in the case of TSP. The AMM of quarks induces magnetic inhibition, causes inverse magnetic catalysis at finite temperature, and the neutral pion mass decreases with magnetic field, while the charged pion mass shows nonmonotonic behavior with respect to the magnetic field, which qualitatively agrees with lattice result. However, the magnetic susceptibility is positive at low temperature with AMM. Also, it is found that the Gell-Mann-Oakes-Renner relation breaks down when the AMM or TSP effect is considered.

Near the critical point in the QCD phase diagram, hydrodynamics breaks down at a momentum where the frequency of the fastest hydrodynamic mode becomes comparable with the decay rate of the slowest nonhydrodynamic mode. $\mathrm{Hydro}+$ was developed as a framework which extends the range of validity of hydrodynamics beyond that momentum value. This was achieved through coupling the hydrodynamic modes to the slowest nonhydrodynamic mode. In this work, analyzing the spectrum of linear perturbations in $\mathrm{Hydro}+$, we find that a slow mode falls out of equilibrium if its momentum is greater than a characteristic momentum value. That characteristic momentum turns out to be set by the branch points of the dispersion relations. These branch points occur at the critical momenta of so-called spectral curves and are related to the radius of convergence of the derivative expansion. The existence of such a characteristic momentum scale suggests that a particular class of slow modes has no remarkable effect on the flow of the plasma. Based on these results, we show that there is an enhancement of the speed of sound due to the $\mathrm{Hydro}+$ corrections compared to the known thermodynamic corrections near the critical point. This enhancement can not exceed a temperature-dependent upper bound which we derive near the critical point in the QCD phase diagram.

We consider the renormalization properties of non-Hermitian Yukawa theories involving a pseudoscalar (axion) field at or near four dimensions. The non-Hermiticity is $\mathcal{P}\mathcal{T}$ symmetric where $\mathcal{P}$ is a linear operator (such as parity) and $\mathcal{T}$ is an antilinear idempotent operator (such as time reversal). The coupling constants of the Yukawa and quartic scalar coupling terms reflect this non-Hermiticity. The path integral representing the field theory is used to discuss the Feynman rules associated with the field theory. The fixed point structure associated with the renormalization group has $\mathcal{P}\mathcal{T}$ symmetric and Hermitian fixed points. At two loops in the massless theory, we demonstrate the flow from Hermitian to non-Hermitian fixed points. From the one-loop renormalization of a massive Yukawa theory, a self-consistent Nambu–Jona-Lasinio gap equation is established and its real solutions are discussed.

Motivated by the experimental search for the QCD critical point, we perform simulations of a stochastic field theory with purely relaxational dynamics (model A). We verify the expected dynamic scaling of correlation functions. Using a finite size scaling analysis, we obtain the dynamic critical exponent $z=2.026(56)$. We investigate time dependent correlation functions of higher moments $M^n(t)$ of the order parameter $M(t)$ for $n=1$, 2, 3, 4. We obtain dynamic scaling with the same critical exponent $z$ for all $n$, but the relaxation constant depends on $n$. We also study the relaxation of $M^n(t)$ after a quench, where the simulation is initialized in the high temperature phase, and the dynamics is studied at the critical temperature $T_c$. We find that the evolution does not follow simple scaling with the dynamic exponent $z$, and that it involves an early time rise followed by late stage relaxation.

The form factors of the semileptonic $B$, $B_s$, and $B_c$ meson decays are calculated in the framework of the relativistic quark model based on the quasipotential approach in QCD. They are expressed through the overlap integrals of the meson wave function. All relativistic effects are consistently taken into account. The momentum transfer $q^2$ behavior of form factors is determined in the whole accessible kinematical range. We do not use any extrapolations, heavy quark $1/m_Q$ expansion, or model assumptions about the shape of form factors. Convenient analytic expressions of the form factors are given, which very accurately reproduce the numerical results of our calculation. On the basis of these form factors and helicity formalism, the differential and total branching fractions of various semileptonic decays of bottom meson are calculated. The mean values of the forward-backward asymmetry $⟨A_{\mathrm{FB}}⟩$, lepton-side convexity parameter $⟨C_F^{\ell }⟩$, longitudinal $⟨P_L^{\ell }⟩$ and transverse $⟨P_T^{\ell }⟩$ polarization of the charged lepton, and the longitudinal polarization fraction $⟨F_L⟩$ for final-state vector meson are also evaluated. We present a detailed comparison of the obtained predictions with the calculations based on the covariant light-front quark model and confront them to available lattice QCD and experimental data. It is found that although both models predict close values of the total branching fractions, the differential distributions and forward-backward asymmetry and polarization parameters differ significantly, especially for the heavy-to-light semileptonic decays. We identify observables which measurement can help to discriminate between models.

We propose a method to create a star orbiting in an asymptotically AdS spacetime using the $\mathrm{AdS}/\mathrm{CFT}$ correspondence. We demonstrate that by applying an appropriate source in the quantum field theory defined on a 2-sphere, the localized star gradually appears in the dual asymptotically AdS geometry. Once the star is created, the angular position can be observed from the response function. The relationship between the parameters of the created star and those of the source is studied. We show that information regarding the bulk geometry can be extracted from the observation of stellar motion in the bulk geometry.

We present an alternative route to investigate quantum forces in a cavity, for both a free scalar field and a free fermionic field. Considering a generalized Matsubara procedure, we compute the quantum pressure on the boundaries of a compactified space in a thermal bath. Also, considering both periodic and antiperiodic boundary conditions in the cavity, we discuss the attractive or repulsive character of the quantum forces. Our results highlight the relevance and interdisciplinarity of the generalized Matsubara procedure as a theoretical platform to manage quantum phenomena in nontrivial topologies.

The cosmological memory effect is a permanent change in the relative separation of test particles located in a Friedmann-Lemaítre-Robertson-Walker (FLRW) spacetime due to the passage of gravitational waves. In the case of a spatially flat FLRW spacetime filled with a perfect fluid in general relativity, it is known that only tensor perturbations contribute to the memory effect while scalar and vector perturbations do not. In this paper, we show that in the context of scalar-tensor theories, the scalar perturbations associated to the scalar graviton contribute to the memory effect as well. We find that, depending on the mass and coupling, the influence of cosmic expansion on the memory effect due to the scalar perturbations can be either stronger or weaker than the one induced by the tensor perturbations. As a byproduct, in an appendix, we develop a general framework which can be used to study coupled wave equations in any curved spacetime region which admits a foliation by time slices.

In this work, we investigated the motion of spinning test particles around a rotating wormhole, extending, in this way, the previous work of Benavides-Gallego et al. [Phys. Rev. D 101, 124024 (2020)] to the general case. Using the Mathisson-Papapetrou-Dixon equations, we study the effective potential, circular orbits, and the innermost stable circular orbit (ISCO) of spinning test particles. We found that both the particle and wormhole spins affect the location of the ISCO significantly. On the other hand, similar to the nonrotating case, we also found two possible configurations in the effective potential: plus and minus. Furthermore, the minimum value of the effective potential is not at the throat due to its spin $a$, in contrast to the motion of the nonspinning test particles in a nonrotating wormhole, where the effective potential is symmetric, and its minimum value is at the throat of the wormhole. In the case of the ISCO, we found that it increases as the spin of the wormhole $a$ increases, in contrast to black holes where the presence of spin decreases the value of the ISCO. Finally, since the dynamical four-momentum and kinematical four-velocity of the spinning particle are not always parallel, we consider the superluminal bound, finding that the allowed values of the dimensionless particle’s spin $s$ change as the wormhole’s spin $a$ increases.

One of the key observables in a gravitational wave power spectrum from a first order phase transition in the early Universe is the mean bubble spacing, which depends on the rate of nucleation of bubbles of the stable phase, as well as the bubble wall speed. When the bubbles expand as deflagrations, it is expected that the heating of the fluid in front of the phase boundary suppresses the nucleation rate. We quantify the effect, showing that it increases the mean bubble separation, and acts to enhance the gravitational wave signal by a factor of up to order 10. The effect is largest for small wall speeds and strong transitions.

In the past decades, an external forward shock model has been successfully developed to explain the main features of the afterglow emission of gamma-ray bursts (GRBs). In the numerical modeling of the GRB afterglow, some approximations have been made for simplicity, and different groups developed their codes. A robust test of these models/approaches is challenging because of the lack of directly measured physical parameters. Fortunately, the viewing angle inferred from the afterglow modeling is widely anticipated to be the same as the inclination angle of the binary neutron star (BNS) mergers that can be evaluated with the gravitational wave (GW) data. Therefore, in the future, it is possible to calibrate the afterglow modeling with the GW inclination angle measurements. We take three methods, including both analytical estimations and direct simulations, to project the uncertainties of the inclination angle measurements. For some BNS mergers accompanied with electromagnetic counterparts detected in the O4/O5 runs of LIGO/Virgo/KAGRA/LIGO-India detectors, we show that the inclination angle can be determined within an uncertainty of $\le 0.1\mathrm{rad}$, supposing that the Hubble constant is known with an accuracy of $\le 3\%$ and the uncertainty of Hubble flow velocity is within $\sim 1\%$. The off-axis GRB outflow will give rise to afterglow emission, and the most energetic ones may be detectable at the distance of $\sim 100–200\mathrm{Mpc}$ even for a viewing angle of $\ge 0.3\mathrm{rad}$. Such events can thus serve as a robust test of the afterglow modeling approach. We have also evaluated the prospect of resolving the so-called Hubble tension with a single GW/GRB association event. We find out that a $\sim 3\%$ precision Hubble constant is obtainable if the uncertainty of the viewing angle can be constrained to be within $\sim 0.1\mathrm{rad}$, which is expected to be the case for some nearby ($\le 250\mathrm{Mpc}$) bright/on-axis GRBs with a well-behaved afterglow light curve displaying a clear achromatic break at early times.

We perform an anisotropic search for the stochastic gravitational-wave (GW) background by decomposing the gravitational-wave sky into its spherical harmonics components. Previous analyses have used the diffraction limit to define the highest-order spherical harmonics components used in this search. We investigate whether the angular resolution of this search is indeed diffraction-limited by testing our ability to detect and localize simulated GW signals. We show that while using low-order spherical harmonic modes is optimal for initially detecting GW sources, the detected sources can be better localized with higher-order spherical harmonics than expected based on the diffraction limit argument. Additionally, we discuss how the ability to recover simulated GW sources is affected by the number of detectors in the network, the frequency range over which the search is performed, and the method by which the covariance matrix of the GW skymap is regularized. While we primarily consider point-source signals in this study, we briefly apply our methodology to spatially extended sources and discuss potential future modifications of our analysis for such signals.

In this paper, we study the Bose-Einstein condensation of a scalar field with an attractive self-interaction, with or without gravitational interactions. We confirm through full dynamical simulation that the condensation timescale due to self-interaction is inversely proportional to the square of the number density $n$ and the self-coupling constant $g:\tau \propto n^{-2}{g}^{-2}$. We also investigate the condensation timescale when self-interaction and gravity are both important by solving the Gross-Pitaevskii-Poisson equations, and find that the condensation time scales according to an additive model for the cross section. We discuss the relevance of our results to theoretical models of boson star formation by condensation.