We consider the impact of non-power-law spectra of matter perturbations with a bump or with a blue tilt at small scales on the evolution of supermassive black holes (SMBHs) located the innermost part of galaxies. We study SMBHs’ mass growth rate and the epochs of their birth in four cosmological models using N-body simulations of dark matter within the box of $(100\mathrm{Mpc}/h{)}^3$. The simulations were populated with SMBHs using the trinity semianalytic model. We found that the most massive SMBHs at the redshifts $z=5–6$ are similar in all considered cosmologies, including the standard lambda cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model. At larger $z$ the bumpy spectra can provide a tenfold increase (relative to $\mathrm{\Lambda }\mathrm{CDM}$ model) in the masses of individual black holes without requiring super-Eddington accretion or heavy seeds. The nucleation of SMBHs starts at $z\sim 13$, which is earlier than in the standard $\mathrm{\Lambda }\mathrm{CDM}$ model.

We perform a detailed analysis of radial oscillations to discuss dynamical stability in two-fluid neutron stars composed of ordinary nuclear matter and a gravitationally coupled dark matter component. Using a fully relativistic two-fluid formalism, we solve the eigenvalue problem for a coupled system of equations with small-amplitude radial perturbations and derive the critical line corresponding to stability boundaries. We also compare these stability boundary lines obtained from the radial perturbations with those obtained from a generalized turning-point criterion based on extremization of mass and particle numbers, and find that the two methods agree to within better than 1% across the parameter space explored. We consider both mirror dark matter and self-interacting fermionic dark matter models, and examine how microphysical properties—such as nuclear equations of state, dark matter mass, and vector coupling strength—reshape the topology of the stability boundary and gravitational mass contours. Our results reveal the emergence of ultradense and compact stars, with nuclear central densities exceeding single-fluid instability thresholds by factors of two or more, and the appearance of twin-star configurations with identical masses but distinct radii and internal fluid compositions. These findings have direct implications for the interpretation of neutron star observables and motivate future studies involving phase transitions, density discontinuities, or additional interactions in multicomponent stellar systems. In particular, the emergence of exotic stable configurations beyond conventional stability limits underscores the need to reassess standard criteria in light of multifluid dynamics, with significant consequences for multimessenger probes of dense matter—including gravitational wave signals, mass-radius constraints, and postmerger remnants.

Collective neutrino flavor instabilities are believed to be prevalent in core-collapse supernovae and neutron star mergers. This work establishes two points related to instability, both in the spirit of developing a more fundamental understanding of collective flavor dynamics. First, a conservation law related to the lepton number implies that spectral crossings are necessary for instability. Second, the most permissive application of the ergodic hypothesis to neutrino flavor evolution implies that spectral crossings are in fact sufficient for instability. We also discuss flavor thermalization and energy conservation in relation to ergodicity.

We investigated universal relations for compact stars rotating at the Keplerian (mass-shedding) limit, which is highly relevant for understanding the rapidly rotating objects formed in the aftermath of a neutron star-neutron star merger. Our analysis is based on a set of nucleonic equations of state (EoSs) featuring systematic variations in the symmetry energy slope parameter $L_{\mathrm{sym}}$ and the isoscalar skewness parameter $Q_{\mathrm{sat}}$, varied within ranges that are broadly consistent with current laboratory and astrophysical constraints. The global observable properties of isolated maximally rotating stars are examined, focusing on the mass-radius relation, moment of inertia, quadrupole moment, and the Keplerian (maximum) rotation frequency, as well as their variations in the $L_{\mathrm{sym}}\text{−}{Q}_{\mathrm{sat}}$ parameter space. Next, we demonstrate that, in the limit of Keplerian rotation, universal relations remain valid across the same set of EoSs characterized by varying $L_{\mathrm{sym}}$ and $Q_{\mathrm{sat}}$. In particular, we present explicit results for the moment of inertia ($I$) and quadrupole moment ($Q$) as functions of compactness, as well as for the moment of inertia-quadrupole moment relation. All of these relations exhibit excellent universality, with deviations typically within a range from a few percent to 10% across a wide range of parameters. Additionally, we verify for our set of EoSs that the universality of $I\text{−}Q$ holds to higher accuracy (at the level of 1%) in the slow-rotation approximation compared with the Kepler limit, where the relative error increases up to $\lesssim 10\%$. Our findings support the applicability of $I$-Love-$Q$-type universal relations in observational modeling of maximally rotating compact stars and the gravitational wave emitted by them, when accounting for significant variation in the symmetry energy and high-density behavior of the nuclear EoS.

The ${\mathrm{\Lambda }}_c(2940)$, an open-charm baryon discovered in 2006, has sparked interest due to its “low mass puzzle,” paralleling the $X(3872)$ in the charmoniumlike sector. Both states challenge conventional hadronic interpretations, with the $X(3872)$ understood as a $D^{*}\overline{D}$ molecular state and the ${\mathrm{\Lambda }}_c(2940)$ hypothesized as a $D^{*}N$ molecular state. This work investigates the radiative decay modes ${\mathrm{\Lambda }}_c(2940)\to {\mathrm{\Lambda }}_c(2286)\gamma$, ${\mathrm{\Lambda }}_c(2940)\to {\mathrm{\Lambda }}_c(2595)\gamma$, and ${\mathrm{\Lambda }}_c(2940)\to {\mathrm{\Lambda }}_c(2765)\gamma$, analogous to radiative transitions observed in the $X(3872)$. Using the one-boson-exchange model to obtain the $D^{*}N$ molecular spatial wave function as input, we calculate decay widths and their ratios, finding differences with different quantum number assumptions. Our findings underscore the potential of electromagnetic probes in revealing its nature and highlight the need for dedicated experimental studies to validate these theoretical predictions.

We formulate the relativistic dissipative hydrodynamics of a system of quasiparticles from the Boltzmann equation within the ambit of relaxation time approximation with modified collision kernels. We focus on two specific scenarios with single quasiparticle species, (i) the extended relaxation time approximation, and (ii) the novel relaxation time approximation. We find that both approaches lead to equivalent results up to first order in spacetime gradients. We generalize the extended relaxation time approach to incorporate multiple quasiparticle species and obtain the corresponding expressions for the shear (${\eta }_s$) and bulk (${\zeta }_s$) viscous coefficients. As an application, we study the temperature dependence of the transport coefficients of hot QCD medium with quasigluon and (light and strange) quasiquark sectors considering the power law ansatz for the momentum dependence of the relaxation time. We explore the impact of the power law exponent on the ratio ${\zeta }_s/{\eta }_s$. Our study suggests that in comparison to a constant exponent, a temperature dependent exponent in the power law ansatz is more suitable for modeling the quasiparticle dynamics in the relevant temperature regime of heavy ion collision.

We investigate the phenomenology of the charged Higgs boson at the International Linear Collider (ILC) within the framework of the type-X Two-Higgs Doublet Model, where a light charged Higgs boson, with a mass around 200 GeV or even smaller than top quark mass, is still being consistent with flavor physics data as well as with collider experimental data. In the theoretically and experimentally allowed parameter space, the $e^{+}{e}^{-}\to H^{\pm }{W}^{\mp }S$ (with $S=H$, $A$) production processes can yield signatures with event rates larger than those from $e^{+}{e}^{-}\to H^{+}{H}^{-}$ and offer sensitivity to the Higgs mixing parameter $\sin (\beta -\alpha )$. We consider the bosonic $H^{\pm }\to W^{\pm }S$ decays, where the neutral scalar $S$ further decays into a pair of tau leptons. We show, through a detector-level Monte Carlo analysis, that the resulting $[\tau \tau ][\tau \tau ]WW$ final state could be seen at the ILC with at least 500 GeV center-of-mass energy and $500{\mathrm{fb}}^{-1}$ of luminosity.

Pulsars, highly magnetized, rotating neutron stars, can have significant muon abundances in their dense cores, making them promising environments to probe ultralight mediators coupled to muons. The precise measurement of periastron advance in binary pulsar systems provides a sensitive probe of such long-range forces. In this work, we study the periastron advance constraints from binary pulsar systems on the ultralight muonic mediators. We compute the muon number fraction in neutron stars, by properly taking into account the suppression effect of the long-range muonic force. We find that the periastron advance constraints impose the most stringent constraints on ultralight muonic mediators in the mass range of $\simeq ({10}^{-17},2\times {10}^{-15})\mathrm{eV}$, probing muonic couplings as small as $\mathcal{O}({10}^{-21})$, which surpass the limits from LIGO/Virgo gravitational wave measurements, by about an order of magnitude.

Massless overlap fermions in the real representation of two-dimensional $\mathrm{SU}(N_c)$ gauge theories exhibit a mod(2) index due to the rigidity of its spectrum when viewed as a function of the background gauge field—lattice gauge fields on a periodic torus come under two classes: ones that have one set of chirally paired zero modes and ones that do not. Focusing on SU(2) and a single Majorana fermion in an integer representation $J$, we present numerical evidence that shows only one of these classes survives the continuum limit and this depends on the boundary conditions of the fermion and the gauge field. As such, two of the four possible partition functions are zero in the continuum limit. By defining modified partition functions which do not include the zero modes of the overlap fermions in the fermion determinant, we are able to define an expectation value for a fermion bilinear as ratios of two mixed partition functions. This observable is referred to as the topological condensate and has a nonzero expectation value on any finite physical torus and also has a nonzero limit as the size of the torus is taken to infinity. We study the spectral density of fermions and the scaling of the lowest eigenvalue with the size of the torus to show the absence of any spontaneous symmetry breaking but the emergence of zero modes in the infinite volume limit where it is prohibited in finite volume. These results remain the same for $J=1$, 2, 3, and 4. These results motivate us to propose an independent plaquette model which reproduces the correct physics in the infinite volume limit using a single partition function.

It has been argued that the isoscalar and isovector mesons play significant roles in nuclear matter and neutron star structures. We improve the extended linear sigma model with baryons, proposed in our previous work, by introducing the flavor structures constructed from antisymmetric tensors of chiral representations to study these physics. The parameter space of this model is refined with well-reproduced nuclear matter properties at saturation density by the lowest-order Lagrangian, ensuring consistency with vacuum results, such as $f_{\pi }\approx 134\mathrm{MeV}$. The anticipated plateaulike behaviors of the symmetry energy are predicted at intermediate densities, which is crucial for the consistency of GW170817 and the neutron skin thickness of ${\mathrm{Pb}}^{208}$. Subsequently, neutron star structures are calculated using several parameter sets, and the results for the nuclear matter properties at saturation density align with empirical values. It is found that the neutron star structures are sensitive to the couplings between the isovector $a_0$ meson and nucleons and the four-vector meson couplings; small values of both are favorable. Meanwhile, nuclear matter properties at saturation density favor larger values of the latter and are not sensitive to the former. This signifies the statistical significance of neutron star observations when obtaining realistic chiral effective field theories or models at various densities. The parameter set favored by neutron star observations also aligns the behavior of the sound velocity with the conformal limit at high densities relevant to cores of massive stars. It is hoped that the results of this work can guide future studies on the relationship between the microscopic symmetry of strong interactions and macroscopic phenomena.

We report novel theoretical results for the ${\gamma }^{(*)}+N(940){\frac{1}{2}}^{+}\to \mathrm{\Delta }(1700){\frac{3}{2}}^{-}$ transition, utilizing a symmetry-preserving treatment of a $\mathrm{vector}\otimes \mathrm{vector}$ contact interaction (SCI) within the Dyson-Schwinger equation formalism. In this approach, both nucleon $N(940){\frac{1}{2}}^{+}$ and $\mathrm{\Delta }(1232)$’s parity partner $\mathrm{\Delta }(1700){\frac{3}{2}}^{-}$ are treated as quark-diquark composites, with their internal structures governed accordingly by a tractable truncation of the Poincaré-covariant Faddeev equation. Nonpointlike $\mathrm{quark}+\mathrm{quark}$ (diquark) correlations within baryons, which are deeply tied to the processes driving hadron mass generation, are inherently dynamic in the sense that they continually break apart and recombine guided by the Faddeev kernel. For the nucleon, isoscalar-scalar and isovector-axial-vector diquarks dominate, while the $\mathrm{\Delta }(1700){\frac{3}{2}}^{-}$ state includes contributions only from isovector-axial-vector diquarks, because the SCI excludes isovector-vector diquarks. Once the Faddeev wave function of the baryons involved in the electromagnetic transition is normalized, taking into account that its elastic electric form factor must be one at the on-shell photon point, we compute the transition form factors that describe the ${\gamma }^{(*)}+N(940){\frac{1}{2}}^{+}\to \mathrm{\Delta }(1700){\frac{3}{2}}^{-}$ reaction and, using algebraic relations, derive the corresponding helicity amplitudes. When comparing with experiment, our findings highlight a strong sensitivity of these observables to the internal structure of baryons, offering valuable insights. Although the SCI framework has obvious limitations, its algebraic simplicity provides analytical predictions that serve as useful benchmarks for guiding more refined studies within QCD-based Dyson-Schwinger equation frameworks.

We investigate the influence of spin polarization in strongly interacting matter by introducing a finite spin potential, ${\mu }_{\mathrm{\Sigma }}$, which effectively controls the spin density of the system without requiring rotation or specific boundary conditions. Inspired by recent lattice QCD simulations that incorporated such a potential, we implement this approach within an effective QCD framework. Our results show that increasing spin polarization leads to a simultaneous decrease in both the chiral and deconfinement restoration temperatures. The resulting phase structure is qualitatively consistent with lattice findings, and notably, we observe the emergence of a first-order chiral phase transition at low temperature. These results suggest that spin-polarized environments can significantly impact the QCD phase diagram and offer a controlled route for studying spin effects in hot and dense matter.

We investigate the structure and uniqueness of squeezed vacuum states defined by annihilation conditions of the form $(a-\alpha a^{†})|\psi ⟩=0$ and their multimode generalizations, with applications to the thermofield double (TFD) state in quantum field theory. For $N=1$ and $N=2$, we demonstrate that these conditions uniquely define the single- and two-mode squeezed vacua, generated by unitary squeezing operators. A key result is the unitary reformulation of the TFD state, expressed as a product of two-mode squeezing operators, ensuring invertibility and resolving the nonunitary paradox in the Minkowski-Rindler vacuum correspondence. Extending to cyclic annihilation conditions $(a_i-{\alpha }_i{a}_{i+1}^{†})|\psi ⟩=0$ with $a_{N+1}\equiv a_1$, we find that nontrivial squeezed states exist only for $N=2$. For $N>2$, we establish a no-go theorem, proving no normalizable, nontrivial solutions exist, revealing a fundamental limit on cyclic multimode entanglement. These results highlight the bipartite nature of TFD-like entanglement and constrain multipartite generalizations in multiregion quantum field theories.

We introduce the concept of pseudoreality for complex numbers. We show that this concept, applied to quantum fields, provides a unifying framework for two distinct approaches to pseudo-Hermitian quantum field theories. The first approach stems from analytically continuing Hermitian theories into the complex plane, while the second is based on constructing them from first principles. The pseudoreality condition for bosonic fields resolves a longstanding problem with the formulation of gauge theories involving pseudo-Hermitian currents, sheds new light on the resolution of the so-called Hermiticity puzzle, and may allow a consistent minimal coupling of pseudo-Hermitian quantum field theories to gravity. We focus on the $i{\varphi }^3$ cubic scalar theory, obtaining the relevant pseudoreality conditions up to quadratic order in the coupling; a theory of two complex scalar fields with non-Hermitian mass mixing; and the latter’s coupling to a $U(1)$ gauge field. The general principle of pseudoreality, however, is expected to contribute to the ongoing development of the first-principles construction of pseudo-Hermitian quantum field theories, including their formulation in curved spacetimes.

Tests of general relativity (GR) can be systematically biased when our waveform models are inaccurate. We perform a proof-of-principle study of systematic biases in tests of general relativity induced by neglecting lensing effects for millilensed gravitational-wave signals, where the lens mass is typically in the ${10}^3{M}_{\odot }–{10}^5{M}_{\odot }$ range. In particular, we use a nested-sampling Bayesian parameter estimation and model selection analysis of a millilensed signal (without a noise realization) with an unlensed parametrized post-Einsteinian (ppE) recovery model. We find that at the signal-to-noise ratios of 30 and higher, there is a significant bias in the ppE parameter, especially when the source is aligned with the lens mass (the lensing effect is pronounced) and when its total mass is low (the signal duration is long). We use a toy model and the linear signal and Laplace approximations to provide a semianalytic explanation for the trends in the systematic errors found in the nested sampling analysis. Moreover, a Bayes factor analysis reveals that the (unlensed) ppE model is weakly favored over the (unlensed) GR model, and a fitting factor study shows there is a significant loss of signal-to-noise ratio when using the (unlensed) ppE model. Thus, for the typical source parameters and SNRs considered in this work, millilensing-induced systematic biases are unlikely to result in false positive GR deviations.

We study the implications of an isentropic processes applied to a Reissner-Nordström black hole. This process is possible if a black hole absorbs a particle with a specific ratio of energy and charge. We show that such an absorption process is not classically allowed, not only in Einstein gravity but also in several modified gravity theories, indicating that this prohibition is quite generic. However, an isentropic absorption process is quantum mechanically allowed: the particle can penetrate the potential barrier on the event horizon. We compute the probability of this absorption process and compare it to that of semiclassical effects. Nonperturbatively, if this process is accumulated, it is possible that the entanglement entropy can be greater than its Bekenstein-Hawking entropy and violate the entropy-bound relation.

The environment surrounding a black hole or black hole binaries is generally expected to play an important role in understanding various astrophysical phenomena around them. In this paper, we study relativistic, low angular momentum, inviscid, and advective hot accretion flow onto a galactic supermassive black hole dressed with a cold dark matter halo. Focusing on different relativistic dark matter distributions with an inner density spike, we analyze the effect of the dark matter halo on the topology and properties of the accretion flow. Our results show enhancement of disk luminosity in the presence of dark matter, which depends on the nature and properties (halo mass and compactness) of the dark matter distribution. Under the assumptions of our accretion model, the dominant contribution to the disk luminosity for compact and massive halos arises from the inner regions of the accretion flow. Consequently, our analysis indicates that luminosity measurements can serve as an effective probe of the underlying dark matter density spike.

Inspired by an earlier idea of Mashhoon, who suggested to relate the discrete quasinormal resonant modes of a black hole to the bound-state resonances of the corresponding inverted black-hole potential, Völkel [Phys. Rev. Lett. 134, 241401 (2025)] has recently computed numerically, for the first time, the bound-state energy spectrum of the inverted Schwarzschild potential. Motivated by this intriguing work, in the present work we use analytical techniques in order to explore the physical and mathematical properties of the Schwarzschild bound-state resonances. In particular, we derive closed-form compact analytical formulas for the infinite spectrum $\{E_n{\}}_{n=0}^{n=\infty }$ of energy eigenvalues that characterize the inverted (binding) black-hole potential. Interestingly, it is explicitly shown that our analytically derived energy spectrum of the black-hole inverted potential agrees remarkably well with the corresponding numerical data that recently appeared in the physics literature.

It has been recently shown that regular black holes arise as the unique spherically symmetric solutions of broad families of generalizations of Einstein gravity involving infinite towers of higher-curvature corrections in $D\ge 5$ spacetime dimensions. In this paper we argue that such regular black holes arise as the byproduct of the gravitational collapse of pressureless dust stars. We show that, just like for Einstein gravity, the modified junction conditions for these models impose that the dust particles on the star surface follow geodesic trajectories on the corresponding black hole background. Generically, in these models the star collapses until it reaches a minimum size (and a maximum density) inside the inner horizon of the black hole it creates. Then, it bounces back and reappears through a white hole in a different universe, where it eventually reaches its original size and restarts the process. Along the way, we study Friedmann-Lemaître-Robertson-Walker (FLRW) cosmologies in the same theories that regularize black hole singularities. We find that the cosmological evolution is completely smooth, with the big bang and big crunch singularities predicted by Einstein gravity replaced by cosmological bounces.

In certain modified gravity theories that include additional scalar degrees of freedom, compact objects such as black holes and neutron stars may undergo a process known as spontaneous scalarization, in which the scalar field is suddenly activated beyond a certain critical point. Since its discovery, it has been clear that this effect can be understood in many cases as a continuous phase transition, well described by the phenomenological Landau model. Recently, it has been pointed out that spontaneous scalarization can also manifest as a first-order phase transition. In this paper, we take a closer look at the nature of spontaneous scalarization as a phase transition, analyzing in detail cases where it occurs as either a second- or first-order transition, as well as a more unconventional scenario characterized by a negative scalar susceptibility. Critical exponents are explicitly computed, and implications for dynamical scalarization are discussed. Moreover, the dynamics of a first-order phase transition is probed through fully nonlinear numerical simulations.