Recent studies have shown that far-field perturbations to the curvature potential of a black hole spacetime may destabilize its quasinormal mode (QNM) spectrum while only mildly affecting time-domain ringdown signals. In this work, we study the QNM spectrum and ringdown behavior of a Schwarzschild black hole with a far-field perturbation to its physical environment—a thin matter shell with finite surface tension. After accounting for the dynamics of the interaction between GWs and the shell, we find that the fundamental mode can migrate perturbatively or be destabilized by the appearance of new modes with no analog in the vacuum case, much like studies of “bumps” in the curvature potential. However, unlike these previous works, we find that the coupling between metric perturbations and oscillations of the shell also sources weakly damped QNMs, which are exclusive to the polar sector. We then study whether the analysis tools of least-squares QNM fits and the full and rational ringdown filters can clearly identify the signatures of the shell in representative ringdown waveforms. We conclude that ringdown at sufficiently early times is insensitive to the shell; weakly damped QNMs (in the polar sector) and echoes, which may enable the analysis methods considered here to infer the presence of a shell, only appear at late times and are generally weak.

Due to computational barriers, parity violation effects have been grossly neglected in gravitational model-building, creating a significant gap in the landscape of existing models. We present a new algorithm for efficiently computing the particle spectrum for any parity-violating tensorial field theory. It allows us to extract conditions for the absence of massive ghosts without resorting to any manipulation of radicals in cases where the particle masses are irrational functions of the Lagrangian coupling coefficients. We test it against several examples, among which is the most general parity-indefinite Einstein-Cartan/Poincaré gravity that propagates two healthy massive scalars (in addition to the massless graviton). Furthermore, we upgrade the psalter software in the wolfram language to accommodate parity-violating theories. psalter is a contribution to the xact project.

We construct novel Taub–Newman–Unti–Tamburino(Taub-NUT)-like black hole solutions in Einstein-bumblebee gravity with and without a cosmological constant. Unlike the Taub-NUT black hole in Einstein gravity without a cosmological constant, which is Ricci flat, our newly constructed Taub-NUT-like black hole is not Ricci flat. Armed with the Wald formalism, we extensively study the thermodynamics of these black hole solutions. We derive all the thermodynamic quantities, including treating the cosmological constant as a pressure for the Taub-NUT-AdS-like black hole. The validity of the first law and the Smarr relation of these black hole solutions is confirmed.

Bayesian inference with stochastic sampling has been widely used to obtain the properties of gravitational wave (GW) sources. Although computationally intensive, its cost remains manageable for current second-generation GW detectors because of the relatively low event rate and signal-to-noise ratio (SNR). The third-generation (3G) GW detectors are expected to detect hundreds of thousands of compact binary coalescence (CBC) events every year with substantially higher SNR and longer signal duration, presenting significant computational challenges. In this study, we systematically evaluate the computational costs of CBC source parameter estimation (PE) in the 3G era by modeling the PE time cost as a function of SNR and signal duration. We examine the standard PE method alongside acceleration methods including relative binning, multibanding, and reduced order quadrature. We predict that PE for a one-month-observation catalog with 3G detectors could require at least billions of CPU core hours with the standard PE method, whereas acceleration techniques can reduce this demand to less than millions of core hours, which is as high as the cost of analyzing GW events in the past 10 years. These findings highlight the necessity for more efficient PE methods to enable cost-effective and environmentally sustainable data analysis for 3G detectors. In addition, we assess the accuracy of accelerated PE methods, emphasizing the need for careful treatment in high-SNR scenarios.

Systematic errors in detector calibration can bias signal analyses and potentially lead to incorrect interpretations suggesting violations of general relativity. In this study, we investigate how calibration systematics affect black hole (BH) spectroscopy, a technique that uses the quasinormal modes (QNMs) emitted during the ringdown phase of gravitational waves to study remnant BHs formed in compact binary coalescences. We simulate a series of physically motivated, tunable calibration errors and use them to intentionally miscalibrate numerical relativity waveforms. We then apply a QNM extraction method—the rational QNM filter—to quantify the impact of these calibration errors. We find that current calibration standards (errors within 10% in magnitude and 10° in phase across the most sensitive frequency range of 20–2000 Hz) are adequate for BH ringdown analyses with existing observations, but insufficient for the accuracy goals of future upgraded and next-generation observatories. Specifically, we show that for events with a high ringdown signal-to-noise ratio of $\sim 120$, calibration errors must remain $\lesssim 4\%$ in magnitude and $\lesssim 4°$ in phase to avoid introducing biases. While this analysis focuses on a particular aspect of BH spectroscopy, the results offer quantitative benchmarks for calibration standards crucial to fully realize the potential of precision tests of general relativity in the next-generation detector era.

Gravitational-wave memory effects are lasting changes in the strain and its time integrals. They can be computed in asymptotically flat spacetimes using the conservation and evolution equations in the Bondi-Sachs framework. Modified theories of gravity have additional degrees of freedom with their own asymptotic evolution equations; these additional fields can produce differences in the memory effects in these theories from those in general relativity. In this work, we study a scalar-tensor theory of gravity known as the Damour-Esposito-Farèse extension of Brans-Dicke theory. We use the Bondi-Sachs framework to compute the field equations in Bondi-Sachs form, the asymptotically flat solutions, and the leading gravitational-wave memory effects. Although Damour-Esposito-Farèse theory has additional nonlinearities not present in Brans-Dicke theory, these nonlinearities are subleading effects in an expansion in inverse luminosity distance; thus, the two theories share many similarities in the leading (and some subleading) solutions to hypersurface equations, asymptotic symmetries, and types of memory effects. The conservation equations for the mass and angular momentum aspects differ between the two theories, primarily because of the differences in the evolution equation for the scalar field. When used to compute the time dependence of the gravitational-wave memory signals from quasicircular inspirals of binary neutron stars and black-hole–neutron-star binaries, they give rise to new features that are of second-order in a small coupling parameter in this theory. The observational bound that the coupling is small suggests that it would be challenging to use memory effects during the inspiral to distinguish between Brans-Dicke and Damour-Esposito-Farèse theories. Nevertheless, these results can be used to analyze and interpret memory effects from numerical-relativity simulations of binaries in this theory.

We present $n(\ge 4)$-dimensional planar black holes and wormholes with a flat exterior, which are originated by an exact solution in general relativity. The nonvacuum regions of these objects are described by the extended dynamical region inside a nondegenerate Killing horizon of Gamboa’s static plane symmetric solution with a perfect fluid obeying a linear equation of state $p=\chi \rho$ for $\chi \in [-1/3,0)$. The matter field inside the horizon is not a perfect fluid but an anisotropic fluid that may be interpreted as a spacelike (tachyonic) perfect fluid. While it satisfies the null and strong energy conditions in the black hole case, it violates all the standard energy conditions in the wormhole case. The metric on the horizon is not analytic but at least $C^{1,1}$ in the single-null coordinates in both cases, so it is regular and there is no lightlike massive thin shell on the horizon.

We report cosmological results from the Dark Energy Spectroscopic Instrument (DESI) measurements of baryon acoustic oscillations (BAO) when combined with recent data from the Atacama Cosmology Telescope (ACT). By jointly analyzing ACT and Planck data and applying conservative cuts to overlapping multipole ranges, we assess how different $Planck+\mathrm{ACT}$ dataset combinations affect consistency with DESI. While ACT alone exhibits a tension with DESI exceeding $3\sigma$ within the $\mathrm{\Lambda }\mathrm{CDM}$ model, this discrepancy is reduced when ACT is analyzed in combination with Planck. For our baseline DESI DR2 $\mathrm{BAO}+Planck$ $\mathrm{P}\mathrm{R}4+\mathrm{ACT}$ likelihood combination, the preference for evolving dark energy over a cosmological constant is about $3\sigma$, increasing to over $4\sigma$ with the inclusion of type Ia supernova data. While the dark energy results remain quite consistent across various combinations of Planck and ACT likelihoods with those obtained by the DESI collaboration, the constraints on neutrino mass are more sensitive, ranging from $\sum m_{\nu }<0.061\mathrm{eV}$ in our baseline analysis, to $\sum m_{\nu }<0.077\mathrm{eV}$ (95% confidence level) in the CMB likelihood combination chosen by ACT when imposing the physical prior $\sum m_{\nu }>0\mathrm{eV}$.

Dark matter (DM) continues to evade direct detection, but neutron stars (NSs) serve as natural laboratories where even a modest DM component can alter their structure. While many studies have examined DM effects on NSs, they often rely on specific choices of equations of state (EOS) models, assume isotropy, and lack a Bayesian statistical framework, limiting their predictive power. In this work, we present a Bayesian framework that couples pressure-anisotropic nuclear EOS to a self-interacting fermionic DM component, constrained by NICER and GW170817 data. Our results show that DM mass fractions up to $\sim 10\%$ remain consistent with current data, which softens the high-density EOS, leading to reduced stellar radii and tidal deformabilities while requiring negligible pressure anisotropy. Bayesian model comparison reveals no statistically significant preference between pure baryonic and DM-admixed NSs, indicating that DM inclusion enhances physical realism without complexity penalties. However, existing data cannot tightly constrain the DM parameters, and our empirical radius definition introduces a systematic bias toward the DM core configurations. To address this, we therefore introduce the DM radius span $\mathrm{\Delta }{R}_{\chi }\equiv R_{\chi ,\max }-R_{\chi ,\min }$ as a unified diagnostic for DM distributions. This parameter simultaneously characterizes core-halo transition features while exhibiting strong linear correlations ($\mathrm{\Delta }{R}_{\chi }<4\mathrm{km}$) with both DM and baryonic parameters, providing a clear avenue for future constraints. Our approach bridges current limitations and future potential in probing DM through compact star observations.

Superradiance can cause the axion cloud around a rotating black hole to reach extremely high densities, and the decay of these axions can produce a powerful laser. The electric field of these lasers is strong enough that the Schwinger effect may become significant, resulting in the production of an electron-positron plasma. We explore the dynamics between axion lasers and this electron-positron plasma. While there are several mechanisms by which the inclusion of a plasma can impact the laser’s behavior, the most significant of these mechanisms is that the electron-positron plasma imparts an effective mass on the photon. As the plasma frequency increases, axion decay becomes energetically unfavorable, up to the point where the axion no longer decays into photons, shutting off the laser. We find that the impact of the electron-positron plasma on the dynamics of the system depend heavily on the parameters, specifically the axion mass $m_{\varphi }$ and the superradiant coupling $\alpha$, and that we may divide parameter space into three regimes: the unenhanced, enhanced, and unstable regimes. In the unenhanced and enhanced regimes, the system will eventually settle into an equilibrium state, emitting a laser of constant luminosity while the number of axions remains constant. In the unenhanced regime, this equilibrium state can be calculated while neglecting the effects of Schwinger production; in the enhanced regime, the equilibrium luminosity is slightly larger than what it would be without Schwinger production. In the unstable regime, the electron-positron plasma suppresses axion decay to the point where the system is never able to reach equilibrium; instead, the axions continue to grow superradiantly. In all three cases, the production of superradiant axions will eventually cause the black hole to spin down to the point where superradiance ceases.

Decades of progress have culminated in first light for high-energy neutrino astronomy: the identification of the first astrophysical sources of TeV–PeV neutrinos by the IceCube neutrino telescope, the active galactic nuclei NGC 1068 and TXS $0506+056$. Today, the prospect of going beyond first light to build high-energy neutrino astronomy in earnest by discovering many more neutrino sources is hampered by the relatively low rate of neutrino detection and the limited view of the sky afforded by IceCube, the single cubic-kilometer-scale neutrino telescope in operation. Yet, this will not stand for much longer. Already today, and over the next 10–20 years, the combined observations of new neutrino telescopes, larger and distributed around the world, will have the potential for transformative progress. Together, they will increase the global rate of neutrino detection by up to 30 times and continuously monitor the entire sky. Within a new joint analysis network—the Planetary Neutrino Monitoring network ($\mathrm{PLE}\nu \mathrm{M}$)—we make detailed forecasts for the discovery of steady-state astrophysical sources of high-energy neutrinos. We show that a combined analysis of global data will expedite source discovery—in some cases, by decades—and enable the detection of fainter sources anywhere in the sky, discovering up to tens of new neutrino sources.

We investigate nonlinear instabilities stemming from superluminal propagation of information in Israel-Stewart-like models of relativistic viscous fluid dynamics. In relativity, the characteristic speed of propagation of information, $w$, and the speed of the fluid, $v$, allow us to differentiate between regimes of the hydrodynamic equations that are acausal but stable ($w>1$), unstable ($v^2{w}^2\ge 1$), and covariantly ill posed ($w^2\le 0$). As an analytical benchmark, we present a new solution that illustrates these distinct regimes. We compare this analytical solution to the result of a numerical relativistic viscous fluid dynamics solver and confirm that the analytical result can be recovered numerically in the stable regime, whether causal or acausal. The onset of numerical instabilities is further found to occur in the regime predicted by the analytical solution.

We study the sensitivity of the CMS search to displaced showers arising from the decays of long-lived particles in the muon system, within the framework of hidden valley scenarios. To establish our simulation setup, we employ a parametrization of hidden valley theory space and adopt a hybrid strategy where the lifetime is treated as a free parameter to provide model-independent hidden valley quark production cross-section upper limits. Our results indicate that the CMS search is broadly sensitive to variations in hidden valley parameters such as the overall scale and relevant mass ratios, while showing comparatively weak dependence on the number of hidden valley colors or flavors. The exact quantitative results we derive depend on the underlying hadronization model employed and thus, we urge caution in interpreting the results. Within these limitations, we also establish model-dependent limits on the maximum strength of the mediator coupling to hidden valley quarks. Our approach illustrates how one can move beyond simplified model strategies by employing a first-principles-inspired theory setup, while highlighting the theoretical uncertainties inherent in modeling hidden valley phenomenology.

A supercooled phase transition in a nearly conformal dark sector can provide a natural setting for darkogenesis via its out-of-equilibrium dynamics, where a particle-antiparticle number asymmetry in the dark sector can be reprocessed into the visible sector, yielding the observed baryon asymmetry and an asymmetric dark matter. We consider a scenario where the number asymmetry is generated from the decay of a mother particle produced via parametric resonance during the phase transition induced due to its coupling to the dilaton associated with spontaneous breaking of scale invariance. It is shown that the correct baryon asymmetry and dark matter abundance can be realized for a dark phase transition at $\mathcal{O}(1)\mathrm{GeV}$, which can also explain the nanohertz gravitational wave signal reported by pulsar timing array experiments. The scenario will be tested further in neutron-antineutron oscillation experiments.

We consider axions lighter than what their QCD couplings might otherwise suggest. Starting with a ${\mathbb{Z}}_N$ axion, we introduce a small explicit ${\mathbb{Z}}_N$ symmetry-breaking coupling between the Standard Model Higgs boson and a reheaton. This small explicit breaking allows us to populate a large portion of the light axion $m_a-f_a$ plane, removes the $1/N$ tuning in the ${\mathbb{Z}}_N$-axion, and explains why only our sector was reheated. Because of finite temperature effects, axions of this sort undergo either “rigged” misalignment, where the axion misalignment angle is effectively $\pi$ regardless of its initial value, or “shuffled” misalignment, where the initial angle is effectively randomized.

We highlight that the observed concurrence between the baryon and dark matter relic densities can be explained via a parametric coincidence between two distinct production mechanisms: Affleck-Dine baryogenesis and dark matter UV freeze-in. In the Affleck-Dine mechanism, the baryon asymmetry is naturally proportional to the inflationary reheating temperature $T_{\mathrm{rh}}$, which also plays a critical role in setting the relic abundance of UV freeze-in dark matter. Since Affleck-Dine baryogenesis requires flat directions in the potential, the framework is inherently supersymmetric, offering compelling UV freeze-in dark matter candidates such as the gravitino. We outline scenarios in which $T_{\mathrm{rh}}$ simultaneously determines both relic abundances, resulting in a baryon-to-dark matter ratio of order unity that is largely insensitive to $T_{\mathrm{rh}}$. We also discuss the conditions required to avoid Q-ball formation or dark matter production by other mechanisms, such as next-to-lightest supersymmetric particle decays, to preserve the parametric coincidence between baryon and dark matter abundances.

Within the composite Higgs paradigm, partial compositeness has emerged as an elegant mechanism for generating large flavor hierarchies such as are observed in the quark and lepton masses and mixings. This mechanism exploits the strong renormalization group effects of the compositeness dynamics when these are not flavor symmetric. Despite its remarkable properties, at this point it is stringently constrained by the body of flavor- and $CP$-violation tests, so that the compositeness scale must be at least $O(100)\mathrm{TeV}$, beyond the direct reach of proposed colliders. On the other hand, composite Higgs theories with flavor-symmetric strong dynamics, but with realistic flavor-violating hierarchies introduced in an ad hoc manner, can extend the Glashow–Iliopoulos–Maiani mechanism of the standard model and thereby be far less constrained, at the edge of LHC reach and well within reach of future colliders. We show how the best features of both of these types of dynamics can be combined if flavor symmetries of the strong composite dynamics are emergent in the IR near the compositeness scale but absent in the far UV. In this case, flavor hierarchies can be generated by the renormalization group flow in the UV, followed by an IR stage in which the dynamics flows towards accidental flavor and $CP$ symmetries. We point out how the collider and low-energy phenomenology is significantly impacted by the IR stage. Our analysis includes a discussion of the distinctive features of the small neutrino masses and their large mixings.

Ultralight vector dark matter induces metric fluctuations that generate timing residuals in the arrival times of pulsar emissions through two distinct modes: a fast mode, sourced by coherent field oscillations, and a slow mode, arising from interference patterns. These modes enable the detection of vector dark matter with masses $m\sim {10}^{-24}–{10}^{-22}\mathrm{eV}$ and $m\sim {10}^{-18}–{10}^{-16}\mathrm{eV}$, respectively, using pulsar timing arrays. While previous studies have explored the fast mode, they neglect the full statistical treatment of the vector field and a precise treatment of its polarization structure. In this work, we investigate the timing residuals from both modes, fully accounting for the statistical properties of ultralight vector dark matter, assuming equipartition among its three polarization states. The two-point correlation functions of timing residuals that we derive serve as direct tools for identifying vector dark matter signatures as a stochastic background in pulsar timing data.

We study the two-point field-strength correlation $g^2⟨G_{\mu \nu }^a(s)G_{\alpha \beta }^b(s^{\prime })⟩$ in the Landau gauge in SU(2) and SU(3) quenched lattice QCD, as well as the gluon propagator $g^2⟨A_{\mu }^a(s)A_{\nu }^b(s^{\prime })⟩$. The Landau-gauge gluon propagator $g^2⟨A_{\mu }^a(s)A_{\mu }^a(s^{\prime })⟩$ is well described by the Yukawa-type function $e^{-mr}/r$ with $r\equiv |s-s^{\prime }|$ for $r=0.1–1.0\mathrm{fm}$ in both SU(2) and SU(3) QCD. Next, motivated by color-magnetic instabilities in the QCD vacuum, we investigate the perpendicular-type color-magnetic correlation, $C_{\perp }(r)\equiv g^2⟨H_z^a(s)H_z^a(s+r\widehat{\perp }))⟩$ ($\widehat{\perp }$: unit vector on the $xy$ plane), and the parallel-type one, $C_{\parallel }(r)\equiv g^2⟨H_z^a(s)H_z^a(s+r\widehat{\parallel })⟩$ ($\widehat{\parallel }$: unit vector on the $tz$ plane). These two quantities reproduce all the correlation of $g^2⟨G_{\mu \nu }^a(s)G_{\alpha \beta }^b(s^{\prime })⟩$, due to the Lorentz and global SU($N_c$) color symmetries in the Landau gauge. Curiously, the perpendicular-type color-magnetic correlation $C_{\perp }(r)$ is found to be always negative for arbitrary $r$, except for the same-point correlation at $r=0$. In contrast, the parallel-type color-magnetic correlation $C_{\parallel }(r)$ is always positive. In the infrared region of $r\gtrsim 0.4\mathrm{fm}$, $C_{\perp }(r)$ and $C_{\parallel }(r)$ strongly cancel each other, which leads to a significant cancelation in the sum of the field-strength correlations as ${\sum }_{\mu ,\nu }{g}^2⟨G_{\mu \nu }^a(s)G_{\mu \nu }^a(s^{\prime })⟩\propto C_{\perp }(|s-s^{\prime }|)+C_{\parallel }(|s-s^{\prime }|)\simeq 0$. Finally, we decompose the field-strength correlation into quadratic, cubic, and quartic terms of the gluon field $A_{\mu }$ in the Landau gauge. For the perpendicular-type color-magnetic correlation $C_{\perp }(r)$, the quadratic term is always negative, which is explained by the Yukawa-type gluon propagator. The quartic term gives a relatively small contribution. In the infrared region, the cubic term is positive and tends to cancel with the quadratic term, resulting in a small value of $C_{\perp }(r)$.

This paper is a continuation of our studies of multiquark hadrons. The antisymmetrization of their wave functions required by Fermi statistics is nontrivial, as it mixes orbital, color, spin, and flavor structures. In our previous papers we developed a method to find them based on the representations of the permutation group, and derived the explicit wave functions for baryons excited to the first and second shells ($L=1$, 2), tetraquarks $qq\overline{q}\overline{q}$ and hexaquarks ($6q$). Now we apply it to light pentaquarks ($qqqq\overline{q}$), in the S- and P-shells ($L=0$, 1). Using Jacobi coordinates, one can use the hyperdistance approximation in 12-dimensional space. We further address the issue of “unquenching” of baryons, by considering their mixing with pentaquarks, via two channels, through the addition of $\sigma$-like or $\pi$-like $\overline{q}q$ pairs. This mixing is central for understanding of the observed flavor asymmetry of the antiquark sea, the amount of orbital motion issue as well as other nucleon properties.