We study the full time-domain evolution of gravitational perturbations in black hole spacetimes arising in Einstein-Weyl gravity, a renormalizable extension of general relativity containing quadratic curvature corrections. We analyze both Schwarzschild and non-Schwarzschild solutions, focusing on monopole and higher multipole perturbations. Using semianalytical methods based on the Rezzolla-Zhidenko parametrization for approximation of the black hole spacetime and time-domain integration for analysis of evolution of perturbations, we study the late-time behavior of gravitational perturbations. Our results show that the ringdown phase is followed by universal slowly decaying oscillatory tails with the envelope $\psi \propto t^{-5/6}$. We also demonstrate the breakdown of the eikonal correspondence between quasinormal modes and unstable null geodesics, highlighting limitations of the Wentzel-Kramers-Brillouin (WKB) method in this context. Our analysis confirms the range of (in)stability of black holes in Einstein-Weyl gravity found in recent publications.

We assess the universal relations among second-order moments of relativistic stars, namely, the moment of inertia, tidal deformability, and spin-induced quadrupole moment, via reformulated perturbation equations. After constructing the spherical background configuration by solving two ordinary differential equations as usual, these three moments are obtained by solving four additional ordinary differential equations. They are solved numerically from the stellar center to the surface, and we do not need to derive homogeneous solutions for obtaining the quadrupole moment. This small number of ordinary differential equations to be solved enables us to identify the primary variable for each second-order moment. Investigating the profile of these variables in the star, we speculate that their nonmonotonic behavior, enhanced typically for soft equations of state and/or high compactnesses, introduces the variety to the relations among these second-order moments unless the black-hole limit is approached. Because realistic relativistic stars are widely believed to be characterized by stiff equations of state, they enjoy the universal relation to a great extent.

Using the cross-correlation data from the first three observing runs of the LIGO-Virgo-KAGRA collaboration, we search for a gravitational-wave background (GWB) from primordial black holes, arising from the superposition of compact binary coalescence events. We consider both early and late binary formation mechanisms and perform Bayesian parameter inference. From the nondetection of the GWB, we provide constraints on the fraction of primordial black holes contributing to the present dark matter energy density.

Bouncing cosmologies, while offering a compelling alternative to inflationary models, face challenges from the growth of vector perturbations during the contracting phase. While linear vector instabilities can be avoided with specific initial conditions or the absence of vector degrees of freedom, we demonstrate the significant role of secondary vector perturbations generated by nonlinear interactions with scalar fluctuations. Our analysis reveals that in a broad class of single-field matter-bounce scenarios, these secondary vector perturbations get unacceptably large amplitudes, provided the curvature fluctuations are consistent with cosmic microwave background observations. This finding underscores the crucial importance of scalar-induced vector perturbations in bouncing cosmology and highlights the need for further investigation into their potential impact on the viability of these models.

A number of important cosmological questions can be addressed only by probing perturbation modes on the largest accessible scales. One promising probe of these modes is the Kamionkowski-Loeb effect, i.e., the polarization induced in the cosmic microwave background (CMB) by Thomson scattering in galaxy clusters, which is proportional to the CMB quadrupole measured at the cluster’s location and look-back time. We develop a Fisher formalism for assessing the amount of new information that can be obtained from a future remote quadrupole survey. To demonstrate the constraining power of such a survey, we apply our formalism to a model that suppresses the primordial power spectrum on large scales but is poorly constrained with existing CMB data. We find that the constraints can be improved by over $3\sigma$ for a survey that measures around 100 clusters over 20% of the sky with a signal-to-noise ratio of 3. In the most optimistic case with a low-noise survey with dense full-sky coverage and only a single degree of freedom in the theory, the constraint improves to over $7\sigma$ beyond local CMB data. Our formalism, which is based in real space rather than harmonic space, can be used to explore a wide range of survey designs, and our results paint an optimistic picture for the utility of remote quadrupole measurements to probe physics on the largest observable scales in the Universe.

We investigate the one-loop quantum correction to the primordial curvature power spectrum in the ultraslow-roll (USR) inflation scenario, incorporating the backreaction effect from curvature perturbations. In the spatially flat gauge, we expand the background inflation field up to second order and identify the one-loop-level backreaction term in the action. Utilizing a gauge transformation, we derive the comoving curvature interaction Hamiltonian in the presence of the backreaction term and calculate the one-loop correction using the in-in formalism. Our results reveal that the one-loop superhorizon corrections previously reported in the literature are canceled by the backreaction contributions. This finding underscores the importance of accounting for backreaction effects in the analysis of quantum corrections during USR inflation.

Despite overwhelming observational evidence for dark matter, we still have no evidence of direct detection. Consequently, our knowledge about dark matter is limited, for example, we do not know if dark matter is a stable particle or if it decays. Without a theoretical particle model, the parameter space of possible decay models is highly variable, and astrophysical or cosmological means of indirectly constraining the phenomenological models are required. This paper investigates a scenario in which a dark matter decays and the dark daughter particle moves with respect to the comoving mother particle. The model is parametrized by the decay rate and the injection velocity of the dark matter particles, which can be converted to the mass ratio. In previous work, a simpler model was used to investigate the evolution of cosmic voids typified as regions with low content of galaxies and nonbaryonic matter. It was found that the growth of S-type voids is modified by the dark matter decay, leading to imprints at the present day. Here we extend our study and improve the method used to model the decay. We also study the gravitational weak-lensing signal that will be able to detect or constrain the parameter space of decaying dark matter. The results of this study suggest that future weak lensing surveys may provide unique probes of the phenomenological parameters of dark matter.

Gravitational waves emitted by binary neutron-star inspirals carry information on components’ masses and tidal deformabilities, but not directly radii, which are measured by electromagnetic observations of neutron stars (NSs). To improve the multimessenger astronomy studies of neutron stars, an expression for neutron-star radii as a function of gravitational-wave only data would be advantageous, as it would allow us to compare information from two different channels. In order to do so, a symbolic regression method, pysr, is trained on Tolman-Oppenheimer-Volkoff solutions to piecewise polytropic equation of state (EOS) input to discover an approximate symbolic expression for the neutron-star radius as a function of gravitational-wave measurements only. The approximation is tested on piecewise polytropic EOS NS data, as well as on NS sequences based on selected realistic (nonpolytropic) dense-matter theory EOSs, achieving consistent agreement between the ground truth values and the symbolic approximation for a broad range of NS parameters covering current astrophysical observations, with average radii differences of few hundred meters. Additionally, the approximation is applied to the GW170817 gravitational-wave mass and tidal deformability posteriors, and compared to reported inferred radius distributions.

Positronium spectrum and lifetimes are known with high precision. The situation is different for positronium moving across a magnetic field. The total momentum does not commute with the Hamiltonian and is replaced by the conserved pseudomomentum. The internal dynamics is not separated from the motion of the system as a whole. The Coulomb potential well is distorted and a wide outer potential well is created. We analytically determine the energy spectrum for a broad range of magnetic field and pseudomomentum values. The ground state energy is compared with the result obtained by solving the Bethe-Salpeter equation. The gauge independence of the pseudomomentum expectation value is established. On the pseudomomentum-magnetic field plane we locate the region in which the ground state resides in the outer well. The results may play a role in the suppression of pulsars’ radio emission (polar cap problem).

We characterize the overdensity (spike) of fermionic dark matter (DM) particles around a supermassive black hole (SMBH) within a general relativistic analysis. The initial DM halo distribution is obtained by solving the equilibrium equations of a self-gravitating system of massive fermions at a finite temperature, according to the Ruffini-Argüelles-Rueda (RAR) model. The final fermionic DM spike is calculated around a Schwarzschild SMBH. We explore two possible interpretations for the origin and evolution of the SMBH seed. One corresponds to the traditional scenario, where a small BH mass of ordinary baryonic origin sits at the halo’s center and grows adiabatically. The other scenario is of DM origin, where the dense and degenerate fermion core predicted by the RAR model grows adiabatically by capturing baryons until its gravitational collapse, becoming a heavy SMBH, whose specific value depends on the fermion mass. We study various initial fermionic DM profiles that the theory allows. We show that overall dilute (i.e., Boltzmannian) fermionic DM develops the well-known spike with density profile $\rho \sim r^{-3/2}$. Instead, for semidegenerate fermions with a dense and compact core surrounded by a diluted halo, we find novel spike profiles that depend on the particle mass and nature. In the more general case, fermionic spikes do not develop a simple power-law profile. Furthermore, in some cases, the SMBH depletes the surrounding DM density instead of enhancing it. Thus, the self-consistent inclusion of the DM candidate nature and mass in determining the structure and distribution of DM in galaxies, including the DM spikes around SMBHs, is essential for the specification of DM astrophysical probes such as BH mergers, gravitational waves, or stellar orbits.

We present a new two-fluid conduction scheme to simulate the evolution of an isolated, self-gravitating, equilibrium cluster of stars and collisionless dark matter on secular (gravothermal) timescales. We integrate the equations in Lagrangian coordinates via a second-order, semi-implicit algorithm, which is unconditionally stable when the mass of the lighter species is much less than that of the heavier species. The method can be straightforwardly generalized to handle a multispecies system with a population of stars or components beyond collisionless dark matter and stars. We apply the method to simulate the dynamical evolution of stellar-dark matter systems, exploring the consequences of mass segregation and gravothermal core collapse, and assessing those effects for observed globular clusters and dwarf galaxies in the Local Volume.

Applying the technique of partial-wave analysis, there are cases where more than one set of underlying complex-valued amplitudes can describe the measured observables. These ambiguities can sometimes be resolved using additional information, but assumptions are often required. It is known that the partial-wave analysis of two-pseudoscalar meson systems produced in photoproduction with a linearly polarized photon beam is free from discrete ambiguities stemming from the Barrelet zeros when the nucleon spin is ignored. In this article, we show that continuous ambiguities are possible for certain wave sets, even though the discrete ambiguities do not appear. We also explore ways to resolve these ambiguities and determine the maximal amount of information that can be obtained from analyses that suffer from these continuous ambiguities.

Within the standard model effective field theory framework, we set indirect constraints on top quark operators that violate baryon number by one unit above the TeV scale. We find that these constraints are typically many orders of magnitude more stringent than the recently derived direct bounds from collider experiments. Therefore, direct observation of baryon number violation in these top-quark observables at the TeV scale would imply a large fine-tuning among operators across different energy scales. This possibility is not protected under universal radiative corrections or any known symmetry principles.

We study the feasibility of having the ${\mathrm{\Sigma }}^{*}(1430)$ state, predicted within the chiral unitary approach and recently reported by the Belle Collaboration, as corresponding to a state of a nonmolecular nature. Starting from this assumption, since the state is observed in the $\pi \mathrm{\Lambda }$ channel, we allow the coupling to this state and relate the coupling to $\overline{K}N$ and $\pi \mathrm{\Sigma }$ using $SU(3)$ symmetry arguments. We find that it is possible to have such a state with negligible coupling to the molecular components with a bare mass of the state very close to the physical mass of the ${\mathrm{\Sigma }}^{*}(1430)$. Yet this has consequences on other observables, since the width obtained is extremely small and incompatible with the Belle observations, and it leads to abnormally large values of the $\overline{K}N$ effective range. Conversely, such mismatches do not appear for large values of the bare mass of the state, but in this case, we observe that the state develops large molecular components. While one can rule out a largely nonmolecular nature for this state, its properties and detailed nature will need further experimental developments which one can anticipate will be coming in the near future.

We present a self-consistent light-front quark model (LFQM) analysis of the pion’s gravitational form factors (GFFs), incorporating the Bakamjian-Thomas (BT) construction consistently throughout the framework. By uniformly applying the BT formalism to both hadronic matrix elements and their associated Lorentz structures, we achieve a current-component-independent extraction of the pion GFFs $A_{\pi }(t)$ and $D_{\pi }(t)$, thereby eliminating the light-front zero-mode ambiguities that typically hinder conventional LFQM approaches. By tuning the model parameters, we identify an optimal set that successfully reproduces the decay constant and electromagnetic form factor of the pion, while yielding a $D$-term value $D_{\pi }(0)\approx -1$, consistent with predictions from chiral perturbation theory. The $D$-term emerges as a sensitive probe of the pion’s internal dynamics, governing its mechanical radius—the largest among the charge, mass, and mechanical radii. We further examine the pion’s spatial structure via its associated two-dimensional light-front densities, including the momentum density, transverse pressure, and shear stress, all of which satisfy the required normalization and von Laue stability conditions. Our results reveal a detailed mechanical landscape: a centrally peaked momentum density that decreases monotonically; a repulsive pressure near the center (up to $x_{\perp }=0.33\mathrm{fm}$) that transitions to attraction in the outer region; and a shear stress profile peaking at an intermediate distance ($x_{\perp }\approx 0.2\mathrm{fm}$).

We extend our investigation of heavy quark transport coefficients in the effective dynamical quasiparticle model (DQPM)—which reproduces nonperturbative QCD phenomena in the strongly interacting quark-gluon plasma according to lattice QCD data—by including inelastic $2\to 3$ processes with massive gluon radiation, in addition to elastic $2\to 2$ parton scattering. Both elastic and inelastic reactions are evaluated at leading order using DQPM-based effective propagators and vertices, accounting for all channels and their interferences. Based on the obtained matrix elements, we calculate various observables connected to a charm quark. First, we calculate the total cross section of a charm quark with the medium partons as functions of temperature and collision energy. Second, we obtain the drag $\mathcal{A}$ coefficient and $\widehat{q}$ coefficient of a charm quark as functions of temperature and momentum and also compare our results with those obtained using the Zakharov model for the momentum-dependent strong coupling for the elastic and radiative vertices with a heavy quark, highlighting the importance of the choice of the strong coupling in the determination of transport coefficients. Third, we calculate the spatial diffusion coefficient of a charm quark and compare our results with those obtained using other approaches. Finally, we explore the mass dependence of the diffusion coefficient by comparing the results for charm quark, bottom quark, and infinitely heavy quark. We found that inelastic processes can play a significant role in the determination of the transport coefficients at large transverse momenta, but are strongly suppressed at low transverse momenta.

We investigate the hidden-charm pentaquark states with strangeness $S=-1$ ($P_{c\overline{c}s}$) within an off shell coupled-channel approach based on effective Lagrangians that respect heavy-quark spin symmetry, SU(3) flavor symmetry, and hidden local symmetry. All relevant meson-baryon two-body channels composed of low-lying anticharmed mesons and singly charmed baryons with $S=-1$, as well as the $J/\psi \mathrm{\Lambda }$ channel, are included. We find a total of 11 negative-parity states and three positive-parity states. Among the negative-parity states, the $P_{c\overline{c}s}(4338)$ and $P_{c\overline{c}s}(4459)$ can possibly be interpreted as $\overline{D}{\mathrm{\Xi }}_c$ and ${\overline{D}}^{*}{\mathrm{\Xi }}_c$ molecular states, respectively. We identify a second state, $P_{c\overline{c}s}(4472)$, located close to the $P_{c\overline{c}s}(4459)$ but with different spin and width, which may correspond to the structure observed by the Belle Collaboration. Both states are generated from the ${\overline{D}}^{*}{\mathrm{\Xi }}_c$ channel and can be interpreted as spin partners. Their properties are consistent with recent experimental observations, providing strong support for the molecular interpretation of the $P_{c\overline{c}s}$ states. We also observe a two-pole structure near the ${\overline{D}}_s^{*}{\mathrm{\Lambda }}_c$ and $\overline{D}{\mathrm{\Xi }}_c^{\prime }$ thresholds, and find virtual and resonance states in the ${\overline{D}}^{*}{\mathrm{\Xi }}_c^{\prime }$ channel depending on spin-parity.

At nonzero temperatures, the deconfining phase transition can be analyzed using an effective matrix model to characterize the change in holonomy. The model includes gluons and two-dimensional ghost fields in the adjoint representation, or “teens.” As ghosts, the teen fields are responsible for the decrease of the pressure as $T\to T_d$, with $T_d$ the transition temperature for deconfinement. Using the solution of this matrix model for a large number of colors, the parameters of the teen fields are adjusted so that the expectation value of the Polyakov loop is close to the values from the lattice. The shear, $\eta$, and bulk, $\zeta$, viscosities are computed at nonzero holonomy to leading logarithmic order in weak coupling. In the pure glue theory, the value of the Polyakov loop is relatively large in the deconfined phase, $\approx 1/2$ at $T_d$. Consequently, if $s$ is the entropy density, while $\eta /s$ decreases as $T\to T_d$, it is still well above the conformal bound. In contrast, $\zeta /s$ is largest at $T_d$, comparable to $\eta /s$, then falls off rapidly with increasing temperature and is negligible by $\sim 2T_d$.

The energy levels of the $n=1$ and $n=2$ bound states of the ${\mu }^{+}{\mu }^{-}$ atom (true muonium) are calculated starting from a previously derived potential that correctly describes positronium to order ${\alpha }^5$ supplemented by the known ${\alpha }^6$ contributions. All electron vacuum polarization corrections on the true muonium levels are computed to order ${\alpha }^6$. The second-order perturbative contributions from all of the ${\alpha }^4$ and ${\alpha }^5$ terms in the potential are also included. Additional order ${\alpha }^6$ contributions from the two-photon and three-photon annihilation processes are included in the evaluation of the ground state ($1{{}^{3}S}_1-1{{}^{1}S}_0$) hyperfine splitting.