We study the canonical quantization of a massive scalar field on a five dimensional, rotating black hole spacetime. We focus on the case where the spacetime is asymptotically anti-de Sitter and the black hole’s two angular momentum parameters are equal. In this situation the geometry possesses additional symmetries which simplify both the mode solutions of the scalar field equation and the stress-energy tensor. When the angular momentum of the black hole is sufficiently small that there is no speed-of-light surface, there exists a Killing vector which is timelike in the region exterior to the event horizon. In this case classical superradiance is absent and we construct analogs of the usual Boulware and Hartle-Hawking quantum states for the quantum scalar field. We compute the differences in expectation values of the square of the quantum scalar field operator and the stress-energy tensor operator between these two quantum states.

There is mounting theoretical evidence that black hole horizons induce decoherence on a quantum system, say a particle, put in a superposition of locations, with the decoherence functional, evaluated after closure of the superposition, increasing linearly with the time the superposition has been kept open. This phenomenon has been shown to owe its existence to soft modes, that is modes with very low frequencies, of the quantum fields—sourced by the particle—which pierce through the horizon, or also can be understood as coming from the interaction with the black hole described as a thermodynamic quantum system at Hawking’s temperature. Here we investigate the effects of ensuing quantum aspects of the geometry itself of the horizon, in an effective perspective in which the quantum geometry of the horizon is captured by the existence of a limit length or by a horizon area quantization. We show that the discreteness of the energy levels associated to the different geometric configurations might have a strong impact on the results, in particular reducing the decoherence effects even to a negligible level in the case of quanta of area $A_0=\mathcal{O}(1)l_p^2$ or larger, with $l_p$ the Planck length.

We develop a localized particle detector model formulated as a massive quantum field on Minkowski spacetime with the spatial origin excised. To render the problem well-posed at the puncture, we impose boundary conditions at the excised point, which we take to be of Robin type. This setup yields a discrete sector, given by bound-state solutions of the radial equation with real, positive frequencies, which characterizes the detector. We construct the full two-point function and show its decomposition into; (i) the discrete radial bound-state sector, (ii) the boundary condition modified continuous sector, and (iii) the unmodified Dirichlet sector. We then compute the detector field’s stress-energy tensor and prove its covariant conservation. For the specific localized modes in this setup, the discrete-sector contribution cancels in the complete stress-energy tensor, leaving only boundary-condition induced terms. Notably, the discrete modes crucial to localized field-based detectors emerge naturally from the boundary conditions, without ad hoc confining potentials, providing a covariant framework that extends the traditional Unruh-DeWitt paradigm. This mechanism is not restricted to Minkowski spacetime; the same construction can be applied to massive fields on backgrounds with naked singularities, such as conical and global monopole spacetimes, offering a unified route to detector localization in a broad class of geometries.

A few years ago, Bemfica, Disconzi, Noronha, and Kovtun (BDNK) formulated the first causal, stable, strongly hyperbolic, and locally well-posed theory of viscous relativistic hydrodynamics to first order in the gradient expansion. Since their inception, there have been several numerical and analytic studies of the BDNK equations, ranging from astrophysical to holographic applications, which have revealed their promise in modeling relativistic flows when viscous, first-order corrections to ideal hydrodynamics are important. In this paper, we present numerical solutions to the BDNK equations for a 4D conformal fluid in Minkowski spacetime constrained to the surface of a geometric sphere. We numerically solve the underlying equations of motion by use of finite difference methods applied in cubed-sphere coordinates—a multiblock grid structure which regularly and continuously covers the surface of a sphere. We present three test cases of our code: linearized fluid perturbations of constant-background equilibrium states, a smooth, stationary initial Gaussian pulse of energy density, and Kelvin-Helmholtz-unstable initial data. In the Gaussian test case with sufficiently large values of the entropy-normalized shear viscosity, the flow, though initialized in equilibrium, dynamically diverges away from equilibrium and the regime of validity of first-order hydrodynamics as very steep gradients form in the solution, causing convergence to be lost in the numerical simulation. This behavior persists at all grid resolutions we have considered, and also occurs at much higher resolutions in simulations of planar-symmetric ($1+1$)D conformal flows. These solutions provide numerical evidence that singularities in solutions to the BDNK equations can form in finite time from smooth initial data. The numerical methods we employ on the two-sphere can be readily extended to include variations in the radial direction, allowing for full ($3+1$)D simulations of the BDNK equations in astrophysical applications.

We present a measurement of the $B$-mode polarization power spectrum of the cosmic microwave background anisotropies at $32\le \ell <502$ for three bands centered at 95, 150, and 220 GHz using data from the SPT-3G receiver on the South Pole Telescope. This work uses SPT-3G observations from the 2019 and 2020 winter observing seasons of a $\sim 1500{\mathrm{deg}}^2$ patch of sky that directly overlaps with fields observed with the BICEP/Keck family of telescopes and covers part of the proposed Simons Observatory and CMB-S4 deep fields. Employing new techniques for mitigating polarized atmospheric noise, the SPT-3G data demonstrates a white noise level of 9.3 $(6.7)\mathrm{\mu }\mathrm{K}\text{−}\mathrm{arcmin}$ at $\ell \sim 500$ for the 95 GHz (150 GHz) data, with a $1/\ell$ noise knee at $\ell =128$ (182). We fit the observed six auto- and cross-frequency $B$-mode power spectra to a model including lensed $\mathrm{\Lambda }\mathrm{CDM}$ $B$-modes and a combination of Galactic and extragalactic foregrounds. This work characterizes foregrounds in the vicinity of the BICEP/Keck survey area, finding foreground power consistent with that reported by the BICEP/Keck collaboration within the same region and a factor of $\sim 3$ higher power over the full SPT-3G survey area. Using SPT-3G data over the BICEP/Keck survey area, we place a 95% upper limit on the tensor-to-scalar ratio of $r<0.25$ and find the statistical uncertainty on $r$ to be $\sigma (r)=0.067$.

It is commonly recognized that the primordial scalar spectral index $n_s$ is approximately 0.96–0.975, depending on the dataset. However, this view is being completely altered by the early dark energy (EDE) resolutions of the Hubble tension, known as the most prominent tension the standard $\mathrm{\Lambda }$ cold dark matter model is suffering from. In corresponding models with prerecombination EDE, resolving the Hubble tension (i.e., achieving $H_0\sim 73\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$) must be accompanied by a shift of $n_s$ toward unity to maintain consistency with the cosmological data, which thus implies a scale invariant Harrison-Zel’dovich spectrum with $n_s=1$ $(|n_s-1|\simeq \mathcal{O}(0.001))$. In this work, we strengthen and reconfirm this result with the latest ground-based cosmic microwave background data from ACT DR6 and SPT-3G D1, the currently most precise measurements at high multipoles beyond the Planck angular resolution and sensitivity. Our work again highlights the importance of reexamining our understanding of the very early Universe within the broader context of cosmological tensions.

We study the growth of supermassive black holes accounting for both accretion and mergers. The former is informed by observations of the quasar luminosity function (QLF) and the latter by the gravitational wave-background (GWB) recently detected by pulsar timing arrays, while estimates of the present-day black hole mass function provide a boundary condition. The GWB is dominated by the most massive black holes ($\gtrsim {10}^9{M}_{\odot }$). We show that their evolution can be simplified into a two-step process: mergers dominate at $z\le 1$, while accretion peaks at $1.4\le z\le 2$. The large amplitude of the observed GWB suggests a significant number of mergers. We show that this generically implies a higher average Eddington ratio for quasars relative to a scenario in which mergers are negligible. In the absence of mergers, matching local estimates of black hole abundance to the QLF implies a radiative efficiency of ${\epsilon }_r=0.12$ and an Eddington ratio of $\lambda =0.2$. With mergers, a progenitor of mass $M_i$ is boosted to a final total mass $M_f$, and there is a direct relation between the mass gained in mergers and the average Eddington ratio of the quasar population, given by $M_f/M_i=(1+\overline{q}{)}^N\sim \lambda /0.2$, where $\overline{q}$ is the average mass ratio, and $N$ is the average number of mergers. There is thus a tension between the observed GWB, quasar properties, and the BH mass function: estimates of the mass function consistent with Eddington ratios inferred in quasars and ${\epsilon }_r\sim 0.1$ underpredict the GWB; multiple/equal mass mergers can boost the GWB but lead to a high Eddington ratio. If the local mass function is on the high end of current estimates, the GWB is more readily explained but requires low efficiencies ${\epsilon }_r\sim {10}^{-2}$ not expected in standard luminous accretion models. The significant merger rate implied by the GWB also strongly suggests that the most massive BHs in the local universe have significant spin due to the orbital angular momentum from mergers, perhaps $a\sim 0.5$.

The suppression of cosmological structure at small scales is a key signature of dark matter (DM) produced via freeze-in in the low-mass regime. We present a comprehensive analysis of its impact, incorporating recent constraints from Milky Way satellite counts, strong gravitational lensing with James Webb Space Telescope (JWST) data, and the Lyman-$\alpha$ forest. We adopt a general strategy to translate existing warm dark matter (WDM) bounds into lower mass limits for a broad class of DM candidates characterized by quasithermal phase space distributions. The benefits of this approach include computational efficiency and the ability to explore a wide range of models. We derive model-independent bounds for DM produced via two-body decays, scatterings, and three-body decays, and apply the framework to concrete scenarios such as the Higgs portal, sterile neutrinos, axionlike particles, and the dark photon portal. Results from specific models confirm the validity of the model-independent analysis.

We present high-precision lattice results for the confined-deconfined interface tension and the latent heat of pure $\mathrm{SU}(N)$ gauge theories up to $N=10$ and investigate their asymptotic $N$ dependency. For both quantities we observe the leading $N^2$ behavior and subleading corrections, with the result for the interface tension $\sigma /T_c^3=0.0182(7)N^2-0.194(15)$ and for the latent heat $L/T_c^4=0.360(6)N^2-1.88(17)$. We use the mixed phase ensemble method—where the system is constrained so that half of the volume is in the confined phase and the other half in the deconfined phase—and the interface tension is obtained by measuring the capillary wave fluctuation spectra of the interfaces between the two phases. The method bypasses supercritical slowing down from which other methods for determining the interface tension suffer, and as a by-product produces accurate estimates of the critical inverse gauge coupling as a function of the inverse temperature. We use the latter to determine the lattice beta function values, required to compute the latent heat from the discontinuity in the average plaquette action across the confined-deconfined transition.

Within the framework of an equivparticle model employing mean-field approximation, we investigate systematically the mass spectra of color-singlet $N$-quark configurations with $N=3$, 6, 9, 12, 15, and 18, which are assumed to be spherically symmetric with quarks occupying the $1{\mathrm{s}}_{1/2}$ state, i.e., compact multibaryon states. At a given quark number $N$, these states collectively form a single irreducible representation under SU(6) symmetry. Our analysis yields comprehensive mass formulas that characterize these SU(6) multiplets, providing a unified description of their mass spectra. In order to effectively constrain the parameter space of the model and improve the prediction accuracy, we carry out a Bayesian parameter inference based on the experimental masses of eight baryons and $D_{03}$. The posterior probability density functions and their correlations of the model parameters are examined, based on which we further predict the masses of various multibaryon states and provide their 68% and 90% credible intervals. In our prediction, H-dibaryon, $D_{03}$, and the dibaryon with $S=-6$ are all bound states relative to $\mathrm{\Lambda }\mathrm{\Lambda }$, $\mathrm{\Delta }\mathrm{\Delta }$, and $\mathrm{\Omega }\mathrm{\Omega }$ thresholds, while slight probabilities of other stable dibaryons (23.64% more stable than ${\mathrm{\Omega }}^{-}{\mathrm{\Xi }}^0$ for the state with $I=\frac{1}{2}$, $S=-5$ and 92.49% more stable than ${\mathrm{\Xi }}^0{\mathrm{\Xi }}^{-}$ for the state wtih $I=0$, $S=-4$) and tribaryons (0.25% more stable than ${\mathrm{\Xi }}^{-}{\mathrm{\Xi }}^0{\mathrm{\Xi }}^0$ for the state wtih $S=-6$, $I=1/2$; 2.19% more stable than $\mathrm{\Lambda }{\mathrm{\Xi }}^0{\mathrm{\Xi }}^{-}$ for the state with $S=-5$, $I=0$; and 2.21% more stable than $\mathrm{\Lambda }\mathrm{\Lambda }{\mathrm{\Xi }}^0$ for the state with $S=-4$, $I=1/2$) are observed as well. For heavier compact multibaryon states, it is unlikely for them to be stable. The stable and unstable multibaryon states examined in this work may persist in compact stars, which could be helpful for us to understand the essence of pulsarlike objects.

A measurement of event-shape variables is presented, using a data sample produced in a special run with approximately one inelastic proton-proton collision per bunch crossing. The data were collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $64\mathrm{\mu }{\mathrm{b}}^{-1}$. A number of observables related to the overall distribution of charged particles in the collisions are corrected for detector effects and compared with simulations. Inclusive event-shape distributions, as well as differential distributions of event shapes as functions of charged-particle multiplicity, are studied. None of the models investigated are able to satisfactorily describe the data. Moreover, there are significant features common amongst all generator setups studied, particularly showing data being more isotropic than any of the simulations. Multidimensional unfolded distributions are provided, along with their correlations.

The yields of the inverse beta decay events produced by antineutrinos from a certain nuclear reactor fuel component are used by many experiments to check various model predictions. Yet measurements of the absolute yields feature significant uncertainties coming, mainly, from the understanding of the antineutrino detection efficiency. This work presents a simple novel approach to directly determine the ${}^{235}\mathrm{U}$ to ${}^{239}\mathrm{Pu}$ inverse beta decay yield ratio using the fuel evolution analysis. This ratio can be used for a sensitive test of reactor models, while the proposed method, results in smaller systematic uncertainties. The DANSS result on this ratio is one of the most precise among reactor neutrino experiments, yet does not significantly contradict to any previous measurement.

We establish direct evidence for the perturbative distinguishability between black hole microstates and thermal states using the AdS/CFT correspondence. In two-dimensional holographic conformal field theories, we obtain the subsystem fidelity and quantum Jensen-Shannon divergence, both of which provide rigorous lower and upper bounds for subsystem trace distance. This result demonstrates that perturbative quantum gravity corrections break semiclassical indistinguishability, thereby supporting the recovery of information even from a small amount of the Hawking radiation.

We study the chiral symmetry breaking effects of helical magnetic fields in a simple bottom up AdS/CFT model. We explore the instability of the chirally symmetric solution in the presence of the $B$ field and see how it switches off as the wave vector of the helix, $k$, rises, resulting in a first order transition. At low energies the model averages over the helix and the magnetic field is not seen. We show that other sources of chiral symmetry breaking are not directly affected by the helical $B$ field. We provide examples of both magnetic catalysis and inverse magnetic catalysis which switch off at large $k$.

Motivated by the work of Longhi and Materassi, who constructed a realization of the (centerless) ${\mathrm{BMS}}_4$ algebra for the massive Klein-Gordon field in $3+1$ dimensions, we build a realization of the (centerless) massless ${\mathrm{BMS}}_4$ algebra including superrotations. This realization depends only on the momenta in the light cone expressed in celestial coordinates without any reference to the Klein-Gordon field. The quadratic Casimir of the Lorentz algebra is written in terms of a second order differential operator and the volume form plays an essential role in this construction. The ${\mathrm{BMS}}_4$ algebra in terms of vector fields shows its kinematical nature, like the Poincaré algebra. We also construct a dynamical realization of ${\mathrm{BMS}}_4$ from the symplectic structure on the solutions of the massless four-dimensional Klein-Gordon field in terms of quadratic expressions of the Fourier modes and plane waves invariant under translations. Using the Mellin transform, we rewrite the Klein-Gordon field in terms of the boost invariant basis, and write down the corresponding ${\mathrm{BMS}}_4$ realization. We also provide the relation with spherical harmonics, linking our results with the solutions of Longhi-Materassi, which are in fact a subset of ours.

We analyze the spectra of general nonminimal second-order operators. To do this, we derive the local part of the trace of the second Seeley-DeWitt heat kernel coefficient for such operators in a completely model-independent way. Afterwards, we provide three examples to show how our result can be applied in practical scenarios. In particular, we emphasize this discussion when dealing with a toy model of dynamical torsion, which is viewed as a simple instance of higher-spin fields. All our results are compatible with the literature, and we provide a Mathematica notebook with the model-independent results that are written in the paper.

We investigate the absorption and scattering of charged massive scalar waves by the Kerr-Newman black-bounce spacetime when the waves are incident along the rotation axis. We calculate the geometrical and glory scattering cross sections using the classical analytical method, and the corresponding absorption and scattering cross sections using the partial wave method, showing that they are in excellent agreement. Our findings indicate that a faster (slower) rotating spacetime or a more repulsive (attractive) electric force tends to reduce (increase) the absorption cross section and results in larger (smaller) angular widths of the scattered wave oscillations. We find that the rotation parameter exerts a suppressive influence on superradiance, which contrasts with the enhancing effect of the repulsive electric force. It is worth mentioning that the regularization parameter $k$ is found to modify the absorption or scattering cross sections only weakly, but can cause a noticeable reduction of superradiance. To further clarify the role of the parameters in superradiance, we study the energy extraction efficiency in the electric Penrose process. For particles moving along the rotation axis, we find that the influence of the parameters ($a$, $q$, $k$) on this efficiency is consistent with their effects on superradiance. We also discuss potential astrophysical applications, showing that particles in this process could be accelerated to ultrahigh energies in realistic environments, and could therefore be used to constrain black hole parameters. For the effect of field mass, it is found that a heavier scalar field leads to a larger absorption cross section and a wider interference fringe of the differential scattering cross section. When superradiance happens, i.e., the absorption cross section becomes negative, it is also found that the differential scattering cross section only changes smoothly, with no apparent qualitative feature showing up.

We revisit our earlier work and investigate the bound state perturbations in the interior of the Schwarzschild black hole. The bound sates are defined as the perturbations in the interior of the black hole with an imaginary spectrum which are regular at the center of black hole while their time-dependent profile falls off exponentially on the event horizon. Using the scale factor in the expanding direction in the interior of the black hole as the clock, we rewrite the corresponding Regge-Wheeler equation and solve it semianalytically as well as numerically. We confirm that the bound state solutions exist for scalar, vector and axial tensor perturbations. It is shown that for a given value of $\ell >s$, there are total $\ell -s$ such bound states. We obtain the universal lower bound $2GM{\omega }_I>1$ for the spectrum of bound state which is asymptotically saturated in the large $\ell$ limit. Furthermore, we obtain an upper bound on the spectrum of axial perturbations which for large $\ell$ scales like $2GM{\omega }_I\lesssim 0.04{\ell }^4$. As observed recently, these bound states have the curious property that the profile of the total wave function has a nonzero magnitude near the future event horizon.

Ultracompact spinning horizonless spacetimes with ergoregions are subject to the ergoregion instability. We systematically investigate the instability of a massless scalar field in a variety of rapidly spinning Proca stars and boson stars using Wentzel, Kramers, and Brillouin-, frequency-, and time-domain methods. We find universal features in the mode structure: the onset of the instability is signaled by a zero-mode, the mode frequencies and growth rates are related by a simple scaling relation in the small-frequency limit (as found for Kerr-like objects), the mode frequencies approach the orbital frequency of counter-rotating stably trapped null geodesics in the eikonal limit, and for each unstable azimuthal mode only a finite number of overtones and polar modes are exponentially growing. The e-folding times are as short as $\tau \sim {10}^{4}M$ (in terms of the spacetime’s ADM mass $M$). Interestingly, we find a near universal relationship between the frequencies and growth rates across all bosonic stars and also compared with Kerr-like objects. Furthermore, we show that weakly nonlinear backreaction of the instability induces a shift in growth rates as well as emission of gravitational waves; we find evidence that these effects lead to an amplification of the unstable process. This suggests that strongly nonlinear interactions are important during the gravitational saturation of the instability.

As ground-based gravitational-wave (GW) detectors improve in sensitivity, gravitational-wave background (GWB) signals will progressively become detectable. Currently, searches for the GWB model the signal as a power law; however, deviations from this model will be relevant at increased sensitivity. Therefore, to prepare for the range of potentially detectable GWB signals, we propose an interpolation model implemented through a transdimensional reversible-jump Markov chain Monte Carlo algorithm. This interpolation model foregoes a specific physics-informed model (of which there are a great many) in favor of a flexible model that can accurately recover a broad range of potential signals. In this paper, we employ this framework for an array of GWB applications. We present three dimensionless fractional GW energy density injections and recoveries as examples of the capabilities of this spline interpolation model. We further demonstrate how our model can be implemented for hierarchical GW analysis on ${\mathrm{\Omega }}_{\mathrm{GW}}$.