Electromagnetic observations reveal that almost all galaxies have supermassive black holes (SMBHs) at their centers, but their properties, especially their spins, are not fully understood. Some of the authors have recently shown [N. Oshita and D. Tsuna, Phys. Rev. D 108, 104031 (2023)] that rapid spins of more than 0.9, inferred for masses around ${10}^7{M}_{\odot }$ from observations of local SMBHs and cosmological simulations, source long-lived ringdowns that enhance the precision of black hole spectroscopy to test gravity in the near-extreme Kerr spacetime. In this work, we estimate the statistical errors in the SMBH mass-spin inference in anticipation of LISA’s detection of extreme mass ratio mergers. We show that for rapidly spinning SMBHs, more precise mass and spin measurements are expected due to the excitations of higher angular modes. For a near-extremal SMBH of mass ${10}^7{M}_{\odot }$ merging with a smaller BH with mass ratio ${10}^{-3}$ at a luminosity distance of more than or around 5 Gpcs, the measurement errors in the mass and spin of the SMBH would be about 10% and 1%, respectively.

Ultralight bosons can be excited around spinning black holes via black hole superradiance. These boson clouds may play an important role in the orbital evolution of binary black holes. In this work, we investigate the formation and evolution of common envelopes of ultralight boson clouds in comparable mass-ratio black hole binaries. We describe the cloud evolution using gravitational molecular eigenstates and analyze the possible level transitions during orbital decay, as well as the impact on orbital dynamics. We find that the cloud can generally lead to eccentricity growth. In particular, the eccentricity may vary significantly during level transition, leaving an eccentricity of $\mathcal{O}(0.1)$ within the detection band of ground-based gravitational wave detectors.

Initial states of dense matter with nonzero electron chiral imbalance could potentially give rise to strong magnetic fields through chiral plasma instability. Previous work indicated that unless chiral chemical potential is as large as the electron vector chemical potential, the growth of magnetic fields due to the instability is washed out by chirality flipping rate enabled by electron mass. We reexamine this claim in a broader range of parameters and find that at higher temperatures the hierarchy is reversed supporting a growing magnetic field for an initial electron chiral chemical potential much smaller than the electron vector chemical potential. Further, we identify a qualitatively new effect relevant for magnetized hot and dense medium where chiral magnetic effect (CME) sourced by density fluctuation acts as a powerful source of Joule heating. Remarkably, even modest chiral chemical potentials (keV) in such environment can deposit energy densities set by the QCD scale in a relatively short time of the order of a few milliseconds or seconds. We speculate how this mechanism makes CME-driven Joule heating a potentially critical ingredient in the dynamics of turbulent density fluctuation of supernovae and neutron star mergers.

We explore various aspects of semiclassical spin hydrodynamics, where hydrodynamic currents are derived from an expansion in the reduced Planck constant $\hslash$, incorporating both flat and curved spacetimes. After establishing covariant definitions for angular momentum currents, we demonstrate that the conservation of the energy-momentum tensor requires modifications involving the Riemann curvature and the spin tensors. We also revise pseudogauge transformations to ensure their applicability in curved spacetimes. Key assumptions for semiclassical spin hydrodynamics are introduced, enabling studies without explicitly invoking quantum kinetic theory. We derive and analyze the linearized semiclassical spin hydrodynamic equations, proving that spin and fluid modes decouple in the linear regime. As a concrete example, we study the ideal-spin approximation in a dissipative fluid with shear viscosity. This analysis confirms our general result: the damping of spin waves is governed solely by spin relaxation time coefficients, independent of linear fluid perturbations.We also examine the Gibbs stability criterion and reveal its limitations at first order in $\hslash$, signaling the inherent anisotropy of the equilibrium state, which remains unaddressed in current semiclassical spin hydrodynamics formulations. Finally, within a conformal Bjorken flow background and using the slow-roll approximation attractor for the fluid sector, we show that the relaxation of the spin potential is governed by spin relaxation time coefficients, mirroring the damping behavior of spin waves in the linear regime.

We study the impact of general disformal metric transformations on fermions, which shift the gravitational metric by an additional rank-2 tensor. This tensor can in principle be constructed from scalar-field gradients, vector fields, or field-strength contractions. We show this transformation results in the conventional Dirac action being modified by additional kinetic and axial-current couplings that are quadratic in the shifted field. When the field sourcing the metric shift takes on a nontrivial background value, apparent Lorentz-violating effects can result, which we identify as terms in an effective field theory. Assuming the well-motivated cases of scalar and vector ultralight dark matter, we demonstrate that experimental tests of rotation and boost violation imply constraints on the additional kinetic coupling. Even under conservative assumptions, the constraints for vector ultralight dark matter are extremely stringent.

We compute the next-to-eikonal (NEik) power corrections to inclusive deep inelastic scattering (DIS) and semi-inclusive deep inelastic scattering (SIDIS) at low $x$ beyond dipole factorization, which represent the eikonal result. The analysis is restricted to contributions arising from $t$-channel quark exchanges, thereby probing the quark background field of the target. For a transversely polarized virtual photon, the NEik corrections to inclusive DIS are expressed in terms of quark and antiquark collinear parton distribution functions, while the corresponding corrections to SIDIS are formulated in terms of the unpolarized quark transverse-momentum-dependent distribution. In contrast, for a longitudinally polarized photon, the NEik corrections to both inclusive DIS and SIDIS vanish at lowest order in ${\alpha }_s$.

We extend the particle-flow neural assisted simulations (parnassus) framework of fast simulation and reconstruction to entire collider events. In particular, we use two generative artificial intelligence tools, continuous normalizing flows and diffusion models, to create a set of reconstructed particle-flow objects conditioned on truth-level particles from CMS Open Simulations. While previous work focused on jets, our updated methods now can accommodate all particle-flow objects in an event along with particle-level attributes like particle type and production vertex coordinates. This approach is fully automated, entirely written in Python, and GPU-compatible. Using a variety of physics processes at the LHC, we show that the extended parnassus is able to generalize beyond the training dataset and outperforms the standard, public tool delphes.

A sample of $365{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}\to \mathrm{\Upsilon }(4S)\to B\overline{B}$ data collected by the Belle II experiment is used to measure the partial branching fractions of charmless semileptonic $B$ meson decays and determine the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $V_{ub}$. Events containing a signal electron or muon $\ell$ and a fully reconstructed hadronic $B$ decay that constrains the signal kinematics are selected, while the rest of the event defines the hadronic system $X_u$ associated with the signal. To discriminate the signal from the 50-times larger background originating from CKM-favored semileptonic $B$ decays, a template fit is performed in both signal and control regions after applying an optimized selection. The partial branching fraction measured for lepton energies greater than 1 GeV in the signal $B$ meson rest frame is $\mathrm{\Delta }\mathcal{B}(B\to X_u\ell \nu )=(1.54\pm 0.08(\mathrm{stat})\pm 0.12(\mathrm{syst}))\times {10}^{-3}$. From this measurement, using the Gambino, Giordano, Ossola, Uraltsev theoretical framework, $|V_{ub}|=(4.01\pm 0.19_{-0.08}^{+0.07})\times {10}^{-3}$ is determined, where the uncertainties are experimental and theoretical, respectively. This value is consistent with the world average obtained from previous inclusive measurements. Different theoretical predictions and partial branching fractions measured in other phase-space regions, defined by additional selections on the $X_u$ and leptonic system masses, are also used to determine $|V_{ub}|$. This allows for a comparison of the resulting values across theoretical frameworks and phase-space regions.

We propose a stringy description of a system composed of two heavy quarks and two heavy antiquarks, mimicking that in pure $SU(3)$ gauge theory. We present both analytical and numerical studies of the string configurations for rectangular geometries. As an application, we analyze the two lowest Born-Oppenheimer potentials. Our results suggest that, depending on the geometry and quark ordering, the ground state of the $QQ\overline{Q}\overline{Q}$ system may be a hadronic molecule, a tetraquark state, or a superposition of the two. For general geometries, we derive the asymptotic expression for the energy of the tetraquark configuration in the infrared limit and extend this result to multiquark configurations. Here we also demonstrate the universality of the string tension.

We derive the affine tensor associated with the energy and momentum densities of both gravitational and matter fields, the complex pseudotensor, for $f(Q)$ nonmetric gravity, the straightforward extension of the symmetric teleparallel equivalent of general relativity (STEGR), characterized by a flat, torsion-free, nonmetric connection. The local conservation of energy-momentum complex on shell is satisfied through a continuity equation. An important analogy is pointed out between gravitational pseudotensor of teleparallel $f(T)$ gravity, in the Weitzenböck gauge, and the same object of symmetric teleparallel $f(Q)$ gravity, in the coincident gauge. Furthermore, we perturb the gravitational pseudotensor ${{\tau }^{\alpha }}_{\lambda }$ in the coincident gauge up to the second order in the metric perturbation, obtaining a useful expression for the power carried by the related gravitational waves. We also present an application of the gravitational pseudotensor, determining the gravitational energy density of a Schwarzschild spacetime in STEGR gravity, adopting the concident gauge. Finally, analyzing the conserved quantities on manifolds, the Stokes theorem can be formulated for generic affine connections.

Long-term numerical relativity simulations of binary black hole systems in the Spectral Einstein Code (SpEC) code exhibit an unexpected exponential drift of the center-of-mass (CoM) away from the simulation’s origin. In our work, we analyze this phenomenon and demonstrate that it is not a physical effect but rather a manifestation of a gauge artifact. The origin of this drift is the reflection of the gauge waves off the outer boundary of the computational domain. These reflections are introduced by inaccuracies in the gauge boundary condition, specifically, the application of the Sommerfeld condition to the time derivative of the gauge fields. Such an approach fails to completely suppress or correctly absorb the outgoing modes, thereby generating artificial feedback into the simulation. To mitigate this problem, we introduce a modified boundary condition that incorporates an explicit CoM correction source term designed to counteract the CoM motion. Our numerical experiments, performed with the SpEC code, reveal that this new boundary treatment reduces the CoM drift by several orders of magnitude compared to the standard implementation, and does not introduce any unwanted physical artifacts.

Precise measurements of the cosmological impact of dark sector relics can shed light on physics beyond the Standard Model. In this work we present Fisher forecasts on nonthermal light massive relics (LiMR) models for a CMB Stage IV-like experiment and the Simons Observatory—particularly focusing on a model of inflaton/moduli decay giving rise to nonthermally distributed dark sector particles, and also comparing our results with those for sterile particles following the Dodelson-Widrow distribution. Two independent parameters, the effective number of extrarelativistic species $\mathrm{\Delta }{N}_{\mathrm{eff}}$ and the effective mass $M_{\mathrm{sp}}^{\mathrm{eff}}$ of the relic, influence linear cosmological observables. We find $\mathrm{\Delta }{N}_{\mathrm{eff}}$ to be more tightly constrained with $\sigma (\mathrm{\Delta }{N}_{\mathrm{eff}})\sim {10}^{-3}$, for a less abundant, heavier LiMR, which becomes fully nonrelativistic around matter-radiation equality than a more abundant, lighter LiMR, which becomes fully nonrelativistic just after recombination, for which $\sigma (\mathrm{\Delta }{N}_{\mathrm{eff}})\sim {10}^{-2}$. The uncertainties on $M_{\mathrm{sp}}^{\mathrm{eff}}$ differ by a factor of $\sim 3$ between the two cases. Our analysis also reveals distinct parameter correlations: the phenomenological parameters $\{\mathrm{\Delta }{N}_{\mathrm{eff}},M_{\mathrm{sp}}^{\mathrm{eff}}\}$ are found to be negatively correlated for the former case and positively correlated for the latter. We obtain similar projected uncertainties on the cosmological parameters (in either case) for both the inflaton/moduli decay and the Dodelson-Widrow models when the first two moments of the LiMR distribution function, related to the phenomenological parameters, are matched. Finally, by constructing a modified distribution that matches the first two moments of the Dodelson-Widrow but deviates maximally in the third moment, we demonstrate that CMB Stage IV data is not expected to be sensitive to higher moments of the distribution.

In view of recent interest in the role of “dark” radiation in cosmology, such as cosmic gravitational waves, sterile neutrinos, and dark photons, we clarify the definition of adiabatic initial conditions in the kinetic theory of gases in an expanding universe. Without assuming any form for the phase space distribution function, we identify two possibilities: a strong and a weak adiabatic initial condition. The strong one corresponds to the standard adiabatic initial conditions, while the weak one is related to the strong via internal isocurvature fluctuations. We show that both types of adiabatic initial conditions are consistent with the separate universe approach, although the latter requires initial internal isocurvature. In passing, we stress the importance of using the particle local momentum in the phase space to define the notion of adiabatic initial conditions. Doing so, we clarify that a gas of gravitons can have adiabatic initial conditions.

Turbulent coronae of supermassive black holes can accelerate nonthermal particles to high energies and produce observable radiation, but capturing this process is challenging due to comparable timescales of acceleration, cooling, and the development of cascades. We present a time-dependent numerical framework that self-consistently couples proton acceleration—modeled by the Fokker-Planck equation—with leptonic-hadronic radiation. For the neutrino-emitting Seyfert galaxy NGC 1068, we reproduce the neutrino spectrum observed by IceCube while satisfying gamma-ray constraints. We also consider a transient corona scenario, potentially emerging in tidal disruption events like AT 2019dsg, and show that cascade feedback on proton cooling can impact proton acceleration and radiation processes in weaker coronae, producing delayed optical or ultraviolet, x-ray, and neutrino emissions of $\mathcal{O}(100\mathrm{d})$. This flexible tool efficiently models multimessenger signals from both steady and transient astrophysical sources, providing insights in combining particle acceleration and radiation mechanisms.

Ultralight scalars emerge naturally in several motivated particle physics scenarios and are viable candidates for dark matter. While laboratory detection of such bosons is challenging, their existence in nature can be imprinted on measurable properties of black holes (BHs). The phenomenon of superradiance can convert the BH spin kinetic energy into a bound cloud of scalars. In this work, we propose a new technique for directly measuring the mass of a dark cloud around a spinning BH. We compare the measurement of the BH spin obtained with two independent electromagnetic techniques: continuum fitting and iron $\mathrm{K}\alpha$ spectroscopy. Since the former technique depends on a dynamical observation of the BH mass while the latter does not, a mismatch between the two measurements can be used to infer the presence of additional extended mass around the BH. We find that a precision of $\sim 1\%$ on the two spin measurements is required to exclude the null hypothesis of no dark mass around the BH at a $2\sigma$ confidence level for dark masses about a few percent of the BH mass, as motivated in some superradiance scenarios.

Gravitational waves (GWs) are expected to originate from black holes interacting dynamically in dense astrophysical environments. In such environments, given that the velocity and cross section between the interacting black holes are low, dynamical capture may occur. Such events merge on very short timescales with high eccentricities and are expected to be detectable in the LIGO-Virgo-KAGRA (LVK) sensitivity band. In this work, we present a dedicated search for dynamical black hole capture events in the third LVK observing run (O3) with the coherent WaveBurst (cWB) algorithm enhanced with Gaussian mixture modeling (GMM) postproduction. With this we consider two applications of GMM: a weakly modeled approach searching for generic short transients under minimal assumptions, and a population-informed approach, in which the GMM model is provided information on the parameter space occupied by the capture population. Although our search does not find any new significant GW events, we find that an informed GMM approach brings significant sensitivity improvements, enabling the detection of dynamical capture events up to a distance of 1.9 Gpc for a $200M_{\odot }$ equal-mass binary. We present updated upper limit estimates of the rate at 90% confidence, the most stringent of which is $0.15{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$, a 34% improvement with respect to previous observational estimates. Furthermore, while the weakly modeled GMM approach is less sensitive to dynamical capture systems, we find that it is possible for these events to be detected up to a distance of 1 Gpc in the cWB-GMM all-sky short search under minimal assumptions. Finally, with the confident detection of GW190521, we estimate the rate of similar events to be $0.94{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$, assuming the event originated from a dynamical capture.

In this work, we show that ultralight dark photons, which couple to the Standard Model photon through kinetic mixing, can potentially source galactic scale magnetic fields. Although these magnetic fields would be too weak to detect at present in galaxies due to plasma screening effects, we show that dark photons can provide the seed magnetic field strength (${10}^{-20}\mathrm{G}$) required for dynamo amplification in galaxies. Such dynamo-amplified magnetic fields are consistent with observations of $\mathrm{\mu }\mathrm{G}$ strength galactic magnetic fields.

We present a new detailed model of the He I collisional-recombination spectrum based on the most up-to-date atomic data. The model accounts for radiative transfer effects and the influence of a nonzero optical depth in He I lines arising from transitions to the metastable $2{}^3\mathrm{S}$ state. The model reveals substantial deviations in the emissivities of the $\lambda 3889$ and $\lambda 7065$ lines in case of a nonzero optical depth, with previous models systematically underestimating and overestimating them by 5% to 20%, respectively. In the optically thin case, however, our results show good agreement with previous studies. Using the new model, we compute optically thin emissivities for a wide set of UV, optical, and IR He I recombination lines over a fine grid of electron densities and temperatures which are typical for H II regions and planetary nebulae ($1\le n_e\le {10}^4{\mathrm{cm}}^{-3}$, $8000\le T_e\le 22000\mathrm{K}$). In addition, we present new fitting formulas for radiative transfer corrections for several He I lines relevant to optical and near-IR observations, covering $0\le {\tau }_{3889}\le 10$ within the same density and temperature ranges. The accuracy of the obtained approximations is $\lesssim 0.1\%$ within the specified parameter range. These results can be readily implemented in modern codes for determining the primordial ${}^4\mathrm{He}$ abundance and are also applicable to a broader range of spectroscopic analyses of He I emission lines.

We construct exact black hole solutions free of curvature singularities, sourced by dark matter halos described by galactic density profiles. Regularity of the geometry is ensured by adopting the relation $P_r=-\rho$ between radial pressure and density, which is consistent with the phenomenological freedom of halo models. Under the assumptions of regularity and the weak-energy condition, sufficiently dense dark matter halos can give rise to asymptotically flat, singularity-free black holes embedded in a galactic environment. These regular black holes are shown to be stable under axial perturbations. In particular, we obtain solutions corresponding to Einasto and Dehnen-type dark matter profiles. We further compute the shadow radii and Lyapunov exponents associated with photon circular orbits around these black holes.