This study presents a systematic investigation of quasinormal modes (QNMs) for probe fields—massless/massive scalar and Dirac fields—around a charged loop quantum gravity black hole (LQG-BH) characterized by the quantum parameter $b_0$ and the charge parameter $Q$. Through spectral analysis of quasinormal frequencies (QNFs), we uncover a distinct overtone outburst driven by quantum gravity effects, prominently manifested in the scalar field spectrum with the multipole quantum number $l=0$. Both the outburst and its accompanying oscillatory patterns grow more pronounced with increasing overtone numbers. In contrast, massless scalar fields with $l>1$ and Dirac fields exhibit delayed outburst development, with nonmonotonic behavior dominating the first two overtones. Notably, increasing the charge $Q$ universally suppresses quantum-gravity-induced features, including outbursts, nonmonotonicity, and oscillations. Furthermore, we present evidence suggesting the presence of quasiresonances in the massive scalar QNM spectrum, thereby illustrating the potential for the emergence of arbitrarily long-lived modes in this charged LQG spacetime. These findings establish a robust and universal interplay between quantum gravity effects and charge dynamics, providing new insights into the spectral properties of quantum-corrected BHs.

We explore purely metric theories of gravity with second-order equations of motion and a single additional, purely gravitational, propagating, scalar degree of freedom. We identify a subclass of these theories in which this scalar causes a phenomenon similar to black-hole scalarization, which we call curvaturization: around small enough Kerr black holes, the scalar induces a tachyonic instability. This triggers a sudden growth of Ricci curvature and results in a new branch of vacuum black-hole solutions. We study the properties of these black holes both in the static as well as the spinning case.

Orbital resonances in extreme-mass-ratio inspirals (EMRIs) have been proven to be a key feature for accurate gravitational-wave template modeling. Decades of research have led to schemes that can not only model the adiabatic inspiral of such a binary system, but also account for the effects of resonances on their evolution. In this work, we use an effective resonance model that includes analytically derived corrections to the radiation reaction fluxes, to study the combined effects of both dominant (low-order) and subdominant (high-order) orbital resonances in EMRIs. We show that using single, universal shifts for all fluxes overestimates the resonance impact, and therefore individualized shifts for each resonance crossing are needed for accurate modeling. Our analysis reveals that the cumulative effects from multiple resonance crossings can significantly impact the orbital evolution of EMRIs, especially for highly eccentric orbits. Our results provide further evidence that resonance effects have to be included in template production to extract detailed astrophysical parameters from EMRI signals.

In this paper, we present a nonlinear numerical investigation on the dynamical scalarization process of a Reissner-Nordström black hole, incorporating an axionic scalar potential within the framework of the Einstein-Maxwell-dilaton theory. By scrutinizing the evolution of the irreducible mass of the black hole and the value of the scalar field on the apparent horizon across various parameters of the axionic potential, we elucidate the correlations between the final states of scalarized charged black hole and the axionic potential. We observe that the inclusion of the axionic potential can either decrease or increase the irreducible mass of the final scalarized black hole, depending on the strength of the coupling between the dilaton and the electric invariant $F_{\mu \nu }{F}^{\mu \nu }$. Regarding the value of the scalar field on the apparent horizon, we find that it decreases with the inclusion of the axionic potential. Our results contribute to an important understanding of the dynamical scalarization of black holes and the potential configurations of scalar hair with various self-interactions.

We reconsider various C-metric spacetimes describing charged and (slowly) accelerating AdS black holes in different theories of (nonlinear) electrodynamics and revisit their thermodynamic properties. Focusing first on the Maxwell theory, we find a parametrization of the metric where we can eliminate the nontrivial “normalization” of the boost Killing vector which was crucial for obtaining consistent thermodynamics in previous studies. We also calculate the Euclidean action using (i) the standard holographic renormalization and (ii) the topological renormalization, showing that in the presence of overall cosmic string tension the two do not agree. These results are also extended to accelerating black holes in ModMax and RegMax nonlinear electrodynamics. Interestingly, for the latter the electrostatic potential picks up a modification, that remains to be explained, but is consistent with the topological renormalization and the (generalized) Hawking-Ross prescription. Our study indicates that thermodynamics of charged accelerating black holes is far from being completely understood.

We measure the growth of cosmic density fluctuations on large scales and across the redshift range $0.3<z<0.8$ through galaxy clustering and the cross-correlation of the ACT data release 6 cosmic microwave background (CMB) lensing map and galaxies from the Dark Energy Spectroscopic Instrument Legacy Survey, using three galaxy samples spanning the redshifts of $0.3\lesssim z\lesssim 0.45$, $0.45\lesssim z\lesssim 0.6$, $0.6\lesssim z\lesssim 0.8$. We adopt a scale cut where nonlinear effects are negligible, so that the cosmological constraints are derived from the linear regime. We determine the amplitude of matter fluctuations over all three redshift bins using Atacama Cosmology Telescope (ACT) data alone to be $S_8\equiv {\sigma }_8({\mathrm{\Omega }}_m/0.3{)}^{0.5}=0.772\pm 0.040$ in a joint analysis combining the three redshift bins and ACT lensing alone. Using a combination of ACT and Planck data we obtain $S_8=0.765\pm 0.032$. The lowest redshift bin used is the least constraining and exhibits a $\sim 2\sigma$ tension with the other redshift bins; thus we also report constraints excluding the first redshift bin, giving $S_8=0.785\pm 0.033$ for the combination of ACT and Planck. This result is in excellent agreement at the $0.3\sigma$ level with measurements from galaxy lensing, but is $1.8\sigma$ lower than predictions based on Planck primary CMB data. Understanding whether this hint of discrepancy in the growth of structure at low redshifts arises from a fluctuation, from systematics in data, or from new physics is a high priority for forthcoming CMB lensing and galaxy cross-correlation analyses.

Recent observations indicate a $4.9\sigma$ tension between the cosmic microwave background (CMB) and quasar dipoles. This tension challenges the cosmological principle. We propose that if we live in a gigaparsec-scale void, the CMB and quasar dipolar tension can be reconciled. This is because we are unlikely to live at the center of the void, and a within 10% offset from the center will impact the quasars and CMB differently in their dipolar anisotropies. As we consider a large and thick void, our setup can also ease the Hubble tension.

A binary extreme-mass-ratio inspiral (b-EMRI) is a hierarchical triple system consisting of a stellar-mass binary black hole (BBH) orbiting a central Kerr supermassive black hole (SMBH). Although predicted by several astrophysical models, b-EMRIs pose a challenge in waveform modeling due to their complex three-body dynamics and strong relativistic effects. Here we take advantage of the hierarchical nature of b-EMRI systems to transform the internal motion of the small binary into global trajectories around the SMBH. This allows us to use black hole perturbation theory to calculate both the low-frequency gravitational waveform due to its EMRI nature and the high-frequency waveform generated by the inner motion of the BBH. When the inner binary’s separation vanishes, our calculation recovers the standard relativistic adiabatic EMRI waveform. Furthermore, by including the high-frequency perturbation, we find a correction to the waveform as large as the adiabatic order when the frequency matches the quasinormal modes (QNMs) of the SMBH, therefore supporting an earlier proof-of-concept study claiming that the small BBH can resonantly excite the QNMs of the SMBH. More importantly, we find that b-EMRIs can evolve faster than regular EMRIs due to this resonant dissipation through the high-frequency modes. These characteristics distinguish b-EMRI waveform templates from regular EMRI templates for future space-based gravitational wave detectors.

A nearby supernova will carry an unprecedented wealth of information about astrophysics, nuclear physics, and particle physics. Because supernova are fundamentally neutrino driven phenomenon, our knowledge about neutrinos—particles that remain quite elusive—will increase dramatically with such a detection. One of the biggest open questions in particle physics is related to the masses of neutrinos. Here, we show how a galactic supernova provides information about the masses of each of the three mass eigenstates individually, at some precision, and is well probed at JUNO. This information comes from several effects including time delay and the Mikheyev-Smirnov-Wolfenstein effect within the supernova. The time delay feature is strongest during a sharp change in the flux such as the neutronization burst; additional information may also come from a QCD phase transition in the supernova or if the supernova forms a black hole. We consider both standard cases as dictated by local oscillation experiments as well as new physics motivated scenarios where neutrino masses may differ across the galaxy.

We build slowly rotating anisotropic neutron stars using the Hartle-Thorne formalism, employing three distinct anisotropy models—Horvat, Bowers-Liang, and a covariant model—to characterize the relationship between radial and tangential pressure. We analyze how anisotropy influences stellar properties such as the mass-radius relation, angular momentum, moment of inertia, and binding energy. Our findings reveal that the maximum stable mass of nonrotating stars depends strongly on the anisotropy model, with some configurations supporting up to 60% more mass than their isotropic counterparts with the same central density. This mass increase is most pronounced in the models where the anisotropy grows toward the star’s surface, as seen in the covariant model. Furthermore, slowly rotating anisotropic stars adhere to universal relations for the moment of inertia and binding energy, regardless of the chosen anisotropy model or equation of state.

The detection of the neutrino magnetic moment (NMM, ${\mu }_v$) is one of the most significant challenges in physics. The additional energy loss due to NMM can significantly influence the helium flash evolution in low-mass stars. Therefore, studying this process serves as the most robust method to constrain NMM. Using the Modules for Experiments in Stellar Astrophysics stellar evolution code, we investigated the impact of NMM on the helium flash evolution in low-mass stars. We found that NMM leads to an increase in both the critical helium core mass required for the helium flash and the luminosity of the tip of the red giant branch (TRGB). For a typical $Z=1Z_{\odot }$, $M=1.0M_{\odot }$, and ${\mu }_v=3\times {10}^{-12}{\mu }_{\mathrm{B}}$ model, the helium core mass increases by $\sim 5\%$, and the TRGB luminosity increases by $\sim 35\%$ compared to the model without NMM. However, contrary to previous conclusions, our model indicates that the helium flash occurs earlier, rather than delayed, with increasing NMM values. This is because the additional energy loss from NMM accelerates the contraction of the helium core, releasing more gravitational energy that heats the hydrogen shell and increases the hydrogen-burning rate, thereby causing the helium core to reach the critical mass faster and advancing the helium flash. An increase in NMM results in a higher peak luminosity for the first helium flash, a more off-center ignition position, and subflashes with higher luminosities, shorter intervals, and higher frequency. We found that the internal gravity wave (IGW) mixing generated by the helium flash can induce sufficient mixing in the radiative zone, turning the overshoot region into a low-$D_{\mathrm{mix}}$ bottleneck within the stellar interior. The increase in NMM in the model narrows the overshoot bottleneck region, enabling Li to enter the surface convection zone more quickly, thereby enhancing the enrichment effect of IGW mixing on surface Li. For models incorporating both NMM and IGW mixing, the reduction in the overshoot bottleneck region allows them to effectively produce super-Li-rich red clump (RC) stars samples.

We demonstrate that the geodesic dynamics of Bogomol’nyi–Prasad–Sommerfield solitons can be modified by the excitation of Feshbach resonances, or quasibound modes, in a toy model of two scalar fields. A mode-generated force emerges, with a strength determined by the spectral flow of the frequency on the moduli space, and weakened by the coupling between the bound and scattering components of the resonance. Notably, spectral walls persist unaffected by the resonant mode’s exponential decay, as the decay constant vanishes at the spectral wall. Our motivation comes from the ’t Hooft-Polyakov monopoles, which do not present true bound states but long lived semibound excitations. Our findings suggest the existence of spectral walls in the scattering of excited monopoles in three dimensions, whose trajectories may significantly deviate from the geodesic motion in the moduli space of unexcited monopoles.

We present direct observational constraints on tachyons, particles with group velocity greater than $c$ in vacuum in a Lorentz invariant theory. Since tachyons may have no direct couplings to Standard Model particles, the most robust and model independent constraints come from gravitational effects, especially black holes. We compute the Hawking radiation of tachyons from black holes, finding it to be significantly enhanced in the presence of heavy tachyons. For a black hole of mass $M$ and tachyons of mass $m$ with $g$ degrees of freedom, the black hole lifetime is found to be $t_{\mathrm{BH}}\approx 192\pi \hslash M/(g{c}^2{m}^2)$ (or doubled for fermions). This implies that the observation of black holes of a few solar masses, with a lifetime of several billion years, rules out tachyons of mass $m\gtrsim 3\times {10}^9\mathrm{GeV}$. This means there cannot exist any tachyons associated with unification scales or quantum gravity. So while there already exists theoretical reasons to be skeptical of tachyons, our work provides a complementary direct observational constraint.

We show that the holographic Schrödinger equation of light-front chiral QCD, together with the ’t Hooft equation of ($1+1$)-dimensional QCD in the large $N_c$ limit, can simultaneously describe the $\varphi$-meson mass spectroscopy as well as diffractive cross section. We compute the $\varphi$-meson diffractive cross section by utilizing its resulting light-front wave functions (LFWFs), in conjunction with the color glass condensate dipole scattering amplitude. Our predictions for the diffractive cross sections show good agreement with the existing experimental data from HERA at various energies from H1 and ZEUS Collaborations. Additionally, we show that the obtained $\varphi$-meson LFWFs effectively describe its various properties, including the decay constant, distribution amplitudes, electromagnetic form factors, charge radius, and magnetic and quadrupole moments.

We study eccentric equatorial orbits of a stellar-mass black hole around an intermediate-mass slowly rotating Kerr black hole in the presence of gravitational radiation and a dark matter halo. The stellar-mass companion will inspiral toward the central black hole while emitting gravitational waves. The evolution is affected by the dynamical friction force caused by the presence of dark matter surrounding the intermediate-mass black hole at the core. Previous studies have shown that the presence of dark matter can be deduced from the gravitational waveforms. We explore the combined effects of slow-rotation of the central black hole and the presence of the dark matter halo around it on the system’s gravitational wave emission.

Blind continuous gravitational-wave (CWs) searches are a significant computational challenge due to their long duration and weak amplitude of the involved signals. To cope with such problem, the community has developed a variety of data-analysis strategies which are usually tailored to specific CW searches; this prevents their applicability across the nowadays broad landscape of potential CW source. Also, their sensitivity is typically hard to model, and thus usually requires a significant computing investment. We present fasttracks, a massively-parallel engine to evaluate detection statistics for generic CW signals using GPU computing. We demonstrate a significant increase in computational efficiency by parallelizing the brute-force evaluation of detection statistics without using any computational approximations. Also, we introduce a simple and scalable postprocessing which allows us to formulate a generic semianalytic sensitivity estimate algorithm. These proposals are tested in a minimal all-sky search in data from the third observing run of the LIGO-Virgo-KAGRA Collaboration. The strategies discussed here will become increasingly relevant in the coming years as long-duration signals become a standard observation of future ground-based and space-borne detectors.

Topological stars are regular, horizonless solitons arising from dimensional compactification of Einstein-Maxwell theory in five dimensions, which could describe qualitative properties of microstate geometries for astrophysical black holes. They also provide a compelling realization of ultracompact objects arising from a well-defined theory and display all the phenomenological features typically associated with black hole mimickers, including a (stable) photon sphere, long-lived quasinormal modes, and echoes in the ringdown. By completing a thorough linear stability analysis, we provide strong numerical evidence that these solutions are stable against nonradial perturbations with zero Kaluza-Klein momentum.

We investigate the interaction between the dark sectors from the point of view of a dynamical system analysis. A general setup for interacting dark energy models that incorporates both quintessence and phantom fields through a switch parameter, allowing an interaction in the dark sectors, has been considered. In the first part of our analysis, we have not assumed any specific form of the interaction, and in the second part, we invoked examples in a general framework of the interaction. The potentials of the scalar field are classified into two broad classes of potentials: exponential and nonexponential. We identify the potential late-time attractors of the system, which have a complete dark energy domination. From our analysis, it is evident there could be an interaction between the dark sector. The interaction, if any, weakens over time. We find for the quintessence field the transfer of energy from dark matter to dark energy can flip the direction, and on the contrary, for the phantom field, it is only from dark matter to dark energy.

An ultralight electrophilic scalar field can produce a long-range Yukawa-like spatial profile around a rotating, magnetized star when coupled to the constant number density of electrons in either the magnetosphere or the star itself. This long-range scalar field generates an effective scalar charge in the star or its magnetosphere, leading to a long-range force between two compact stars in a binary system. The electrophilic scalar can also radiate from isolated pulsars or double pulsar binary systems. Using the Crab pulsar and PSR J0737-3039A/B as test cases, we derive constraints on the scalar-electron coupling by analyzing observations of long-range force, orbital period decay in binary systems, and pulsar spin-down rates. Among these, the most stringent limits on the coupling are obtained from the orbital period decay. However, these constraints can be significantly reduced if the scalar interacts with the pervasive cosmic neutrino background. Enhancing experimental sensitivity and studying compact objects with stronger magnetic fields and higher angular velocities could further strengthen these bounds.

Low-mass axionlike particles could be produced in abundance within the cores of hot, compact magnetic white dwarf (MWD) stars from electron bremsstrahlung and converted to detectable x-rays in the strong magnetic fields surrounding these systems. In this work, we constrain the existence of such axions from two dedicated Chandra x-ray observations of $\sim 40\mathrm{ks}$ each in the energy range $\sim 1–10\mathrm{keV}$ toward the MWDs WD $1859+148$ and PG $0945+246$. We find no evidence for axions, which constrains the axion-electron times axion-photon coupling to $|g_{a\gamma \gamma }{g}_{aee}|\lesssim 1.54\times {10}^{-25}$ $(3.54\times {10}^{-25}){\mathrm{GeV}}^{-1}$ for PG $0945+246$ (WD $1859+148$) at 95% confidence for axion masses $m_a\lesssim {10}^{-6}\mathrm{eV}$. We find an excess of low-energy x-rays between 1 and 3 keV for WD $1859+148$ but determine that the spectral morphology is too soft to arise from axions; instead, the soft x-rays may arise from nonthermal emission in the MWD magnetosphere.