In this study, we establish a connection between time- and spacelike entanglement entropy. We show that timelike entanglement entropy is closely related to spacelike entanglement entropy and its temporal derivative. For a broad class of states, it can be uniquely determined by a linear combination of spacelike entanglement entropy and its first-order temporal derivative. This relation holds, for instance, in states conformally equivalent to the vacuum in two-dimensional conformal field theories. For more general states, we demonstrate that the relation can be constructed perturbatively. Our results suggest that timelike entanglement entropy is constrained by causality. Moreover, this relation provides a unified framework for time- and spacelike entanglement entropy, within which the imaginary component of timelike entanglement entropy can be understood as arising from the noncommutativity between the twist operator and its first-order temporal derivative.

We investigate the quantization of a single unstable mode in a real scalar field subject to a Robin boundary condition in ($1+1$)-dimensional half-Minkowski spacetime. The instability arises from an imaginary frequency mode—analogous to that of the inverted harmonic oscillator—requiring the rigged Hilbert space formalism for consistent quantization. Within this framework, the unstable mode is naturally described as a well-defined decaying (or growing) quantum state with a characteristic mean lifetime. We investigate its physical consequences via the response of an Unruh-DeWitt detector along static, inertial, and uniformly accelerated trajectories. For static and inertial observers, the detector response exhibits a Breit-Wigner resonance profile, with a decay width determined by the unstable frequency and a Doppler factor. In the Neumann limit, infrared divergences emerge from arbitrarily low-frequency modes. Interestingly, for accelerated detectors, the response acquires a nontrivial dependence on acceleration, and the Neumann limit yields a finite, oscillatory signal rather than a divergence, suggesting that acceleration can act as an effective infrared regulator.

We consider generation from the vacuum of a scalar charged field in a rigidly rotating frame. Adding an external magnetic field opens the way to Bose condensation of the field. This phenomenon has been studied for an external uniform magnetic field occupying the whole volume of the uniformly rotating cylindrical system of finite radius $R$ with a Dirichlet boundary condition imposed on it. In addition to continuing this study, we consider the field formed by a flux tube of small radius. We find numerical solutions of the Gross-Pitaevskii equation for the charged scalar field, the critical rotation frequencies, the mean radii, and the condensate energies and compare them with those found in a linearization scheme and with approximate analytical solutions. We show that for the same input parameters the energy of the condensate in the case of the flux tube is lower than in the case of uniform magnetic field in the whole cylinder.

Precessing binary black-hole mergers can produce a net flux of circularly polarized gravitational waves. This imbalance between left- and right-handed circularly polarized waves, quantified via the Stokes pseudoscalar $V_{\mathrm{GW}}$, originated from mirror asymmetries in the binary. We scan the parameter space of black-hole mergers to investigate correlations between $V_{\mathrm{GW}}$ and chiral magnitudes constructed out of the intrinsic parameters of the binary. To this end, we use both numerical-relativity simulations for quasicircular and eccentric precessing mergers from both the SXS and RIT catalogs, as well as the state-of-the-art surrogate model for quasicircular precessing mergers NRSur7dq4. We find that, despite being computed by manifestly different formulas, $V_{\mathrm{GW}}$ is linearly correlated to the helicity of the final black hole, defined as the projection of its recoil velocity onto its spin. Next, we test our ability to perform accurate measurements of $V_{\mathrm{GW}}$ in gravitational-wave observations through the injection and recovery of numerically simulated signals. We show that $V_{\mathrm{GW}}$ can be estimated unbiasedly using the surrogate waveform model NRSur7dq4 even for signal-to-noise ratios of nearly 50, way beyond current gravitational-wave observations.

We use effective field theory techniques to derive the quadrupole-quadrupole part of the gravitational wave, obtaining a waveform in agreement with previous results found within the multipolar-post-Minkowskian method. This result is obtained by carefully avoiding implicit coordinate transformation, that would also alter the form of the radiation reaction force in the harmonic gauge. An in-in effective action is then derived along the same principles and it is shown to provide energy and angular momentum balance equations consistent with the corresponding fluxes carried at infinity by gravitational radiation.

How long after the merger of two black holes can one rely on linear perturbation theory, and how many quasinormal modes are in the ringdown? Such questions suggest that black hole spectroscopy suffers from systematic uncertainties that potentially spoil ringdown analyses, both from high-accuracy simulations and in data from gravitational wave detectors. In this work, we demonstrate that linear-signal analysis is a powerful tool for quantifying biases, allowing for detailed explorations that are computationally too expensive for traditional Bayesian injection and recovery approaches. We quantify the validity of the Fisher information matrix and bias formula by comparing it to robust but slow Bayesian sampling. Working with flat noise in the time domain, statistical errors and systematic biases can mostly be detected analytically. Due to its efficiency, we provide detailed parameter space analyses for potentially unmodeled small contributions from overtones, quadratic modes, and tails. We find linear signal analysis well suited for predicting biases in simple ringdown models at intermediate signal-to-noise ratios (SNRs) of order 50 when unmodeled effects are small. It is also valuable in explaining ongoing issues in extracting quasinormal modes from high-precision simulations, as one can understand them as high-SNR signals. Therefore, this approach offers promising prospects for improving ringdown models by efficiently identifying and incorporating systematic uncertainties, ultimately enhancing the accuracy and robustness of black hole spectroscopy.

The measurement of deviations in the Kerr metric using gravitational-wave observations will provide a clear signal of new physics. Previous studies have developed multiple parametrizations (e.g., “bumpy” spacetime) to characterize such deviations in extreme mass-ratio inspirals (EMRIs). These approaches often rely on the Fisher information matrix (FIM) formalism to quantify the constraining power of future space-borne gravitational-wave detectors, such as LISA and Tianqin. For instance, using the analytical kludge waveform model under varying source configurations, such methods have achieved constraint sensitivity levels ranging from ${10}^{-4}$ to ${10}^{-2}$ on the dimensionless bumpy parameter $\delta \tilde{Q}$ for LISA. In this paper, we advance prior analyses by integrating particle swarm optimization (PSO) with matched filtering under a restricted parameter search range to enforce a high probability of convergence for PSO. Our results reveal a significant number of degenerate peaks in the likelihood function over the signal parameter space with values that exceed the injected one. This extreme level of degeneracy arises from the involvement of the additional bumpy parameter $\delta \tilde{Q}$ in the parameter space and introduces systematic errors in parameter estimation. We show that these systematic errors can be mitigated using information contained in the ensemble of degenerate peaks, thereby showing a promising potential method for improving local parameter estimation if the other immense challenges of a global search are first solved. This study highlights the critical importance of accounting for such degeneracies, which are absent in FIM-based analyses, and points out future directions for improving EMRI data analysis.

In this paper, we establish a universal equality governing Euclidean integrals of gravitational actions in higher-derivative theories. This relation is shown to hold universally for asymptotically flat black holes in pure gravity, and is generalized to asymptotically anti-de Sitter spacetimes through appropriate regularization. We further examine its validity in systems with matter-gravity coupling, identifying that violations occur only when matter fields exhibit pathological behaviors: divergence at the horizon or nondecaying profiles at infinity. These findings reveal fundamental constraints on gravitational thermodynamics and provide diagnostic tools for identifying ill-behaved matter configurations.

The portion of the gravitational energy absorbed by the black hole due to the radial infall of a point mass is known to diverge at leading order in perturbation theory. This divergence is an artifact of the point-particle model, where the contribution of each multipole to the total absorbed energy is observed to be roughly constant. We show explicitly that this divergent energy arises from the infinite energy present in the singular static field arbitrarily close to the point mass, which also flows into the black hole when the particle trajectory crosses the horizon. We perform a multipole decomposition of the linearized gravitational field generated by the point mass near its world line at the black hole horizon. By applying the standard field-theoretical approach to the particle field, we compute the corresponding partial energy and find that it matches the constant multipole contribution.

This study tackles the impact dark energy (DE) in different systems by a simple unifying formalism. We introduce a parameter space that compares gravity across all cosmic scales, using the McVittie spacetime and connects spherically symmetric solutions with cosmological solutions. By analyzing the invariant scalars—the Ricci, Weyl, and Kretschmann scalars—we develop a phase-space description that predicts the dominance of the cosmological constant. We explore three cases: (i) the local Hubble flow around galaxy groups and clusters, (ii) spherical density distributions, and (iii) binary motion. Our results show that the Kretschmann scalar of galaxy groups and clusters in their turnaround is $2{\mathrm{\Lambda }}^2$, which is 3 times the Kretschmann scalar of the cosmological constant. This indicates the DE domination in local structures.

The $S_8$ value inferred from the Subaru Hyper Suprime-Cam (HSC) Year 3 cosmic shear data, under the assumption of the flat $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model, is $2–3\sigma$ lower than that inferred from observations of the early-time Universe, such as cosmic microwave background (CMB) anisotropy data. Resolving the $S_8$ tension requires a scenario in which structure formation on small scales is suppressed in the late Universe. As potential solutions, we consider extended models both within and beyond the $\mathrm{\Lambda }\mathrm{CDM}$ model—models that incorporate parametrized baryonic feedback effects, the effect of varying neutrino mass, and modified structure growth, each of which can lead to a suppression of structure growth at lower redshifts, with its own distinct scale and redshift dependencies. In particular, we consider phenomenological modified gravity models in which the suppression of structure growth is triggered at lower redshifts, as dark energy ($\mathrm{\Lambda }$) begins to dominate the background expansion. We show that the modified growth factor models—especially those featuring more rapid growth suppression at lower redshifts—provide an improved fit to the combined datasets of the HSC-Y3 cosmic shear correlation functions, the Planck CMB, and the ACT DR6 CMB lensing, compared to the fiducial $\mathrm{\Lambda }\mathrm{CDM}$ model and the models including the baryonic effects or the massive neutrino effect within the $\mathrm{\Lambda }\mathrm{CDM}$ framework.

The origins and acceleration mechanisms of ultra-high-energy cosmic rays (UHECRs) are unknown. Many models attribute their extreme energies to powerful astrophysical jets. Understanding whether jet geometry—specifically the opening angle and its orientation relative to Earth—affects observational signatures is crucial for interpreting UHECR data. In this work, we perform numerical simulations of UHECR propagation in a magnetized universe to investigate the spectral signatures of jetted and nonjetted astrophysical sources. We demonstrate, for the first time, that under certain conditions, emission geometry can play a decisive role in shaping the observed spectrum of individual UHECR sources. These findings provide new insights into the conditions necessary for detecting UHECRs from jets and highlight how the interplay between emission geometry and magnetic fields influences observed energy spectra.

The impact of the inclusion of transverse-momentum-dependent (TMD) shape functions on the transverse momentum spectrum in $J/\psi$ production at the electron-ion collider (EIC) is investigated by considering the matching of the TMD factorization description at low transverse momentum with the collinear factorization description at high transverse momentum by means of the inverse-error weighting method. Despite large uncertainties from scale variations and the $J/\psi$ long-distance matrix elements, predictions for the differential cross section and its $\cos (2{\varphi }_{\psi })$ modulation are obtained. We find that physical constraints are satisfied in case a process-dependent term is included for color octet production, but not in all cases when it is excluded. These numerical results support the analytic calculations in the work by Boer et al. [J. High Energy Phys. 08 (2023) 105.]. Future experimental data can thus test the validity of TMD factorization in $J/\psi$ production and explore the presence of nontrivial process-dependent effects in the soft-gluon resummation. This will be crucial in the extraction of gluon unpolarized and linearly polarized TMD distributions of the proton. In addition, we suggest how the sign of the latter can be determined by investigating the presence of a node in the $\cos (2{\varphi }_{\psi })$ modulation as a function of transverse momentum.

We propose that the Higgs potential, a key element in our understanding of nature, is partially generated by the instantons of new confining dynamics, perhaps from a hidden sector. In this picture, while the Higgs itself is a fundamental field, it controls the strength of the nonperturbative interactions that give rise to its potential. This setup can be realized in “Twin Higgs” hierarchy models, where the twin strong dynamics confines at or above the weak scale, but large quantum corrections to the Higgs potential are avoided. We examine a simple setup in which this instanton contribution is augmented by a quartic term, which is sufficient for a realistic electroweak symmetry breaking mechanism. The minimum of the potential is given by the Lambert $W_0$ function, with these assumptions. We discuss the predictions of this model and how it may be tested through measurements of the Higgs self coupling. Given the connection with nontrivial dynamics, one may also consider the prospects of accessing hidden sector states at colliders; this seems to be typically challenging in our setup. Symmetry restoration in the early Universe in this scenario is briefly examined. We also comment on the possible connection of our general setup with recent work on the physics of field space end points.

We extend the study of exotic matter formation via the TQ4Q1.1 set of collinear, variable-flavor-number-scheme fragmentation functions for fully charmed or bottomed tetraquarks in three quantum configurations; scalar ($J^{PC}=0^{++}$), axial vector ($J^{PC}=1^{+-}$), and tensor ($J^{PC}=2^{++}$). We adopt single-parton fragmentation at leading power and implement a nonrelativistic quantum chromodynamics (NRQCD) factorization scheme tailored to tetraquark Fock-state configurations. Short-distance inputs at the initial scale are modeled using updated calculations for both gluon- and heavy-quark-initiated channels. A threshold-consistent Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution is then applied via the novel heavy-flavor nonrelativistic-evolution (HF-NRevo) hybrid scheme. We provide the first systematic treatment of uncertainties from nonperturbative color-composite long-distance matrix elements (LDMEs), as well as from perturbative hard-scattering (H-MHOUs) and fragmentation-scale inputs (F-MHOUs), assessed separately and in combination. To support phenomenology, we compute $\mathrm{NLL}/{\mathrm{NLO}}^{+}$ cross sections for tetraquark-jet systems at the HL-LHC and FCC within the hybrid collinear and high-energy factorization (HyF) as implemented in (sym)JETHAD, incorporating angular multiplicities as key observables sensitive to high-energy QCD dynamics. We also provide expected event yields based on realistic luminosity scenarios, offering a concrete benchmark for experimental searches. This work connects the investigation of exotic hadrons with state-of-the-art precision QCD.

A key step in any resonant anomaly detection search is accurate modeling of the background distribution in each signal region. Data-driven methods like CATHODE accomplish this by training separate generative models on the complement of each signal region, and interpolating them into their corresponding signal regions. Having to retrain the generative model on essentially the entire dataset for each signal region is a major computational cost in a typical sliding window search with many signal regions. Here, we present SIGMA, a new, fully data-driven, computationally efficient method for estimating background distributions. The idea is to train a single generative model on all of the data and interpolate its parameters in sideband regions in order to obtain a model for the background in the signal region. The SIGMA method significantly reduces the computational cost compared to previous approaches, while retaining a similar high quality of background modeling and sensitivity to anomalous signals.

In this work, we investigate the radiative decays of the ${\mathrm{\Lambda }}_b$ and ${\mathrm{\Xi }}_b$ bottom baryons, which belong to the flavor antitriplet (${\overline{\mathbf{3}}}_{\mathrm{F}}$), within the constituent quark model formalism. The electromagnetic transitions are calculated from the second shell states to both the ground and $P$-wave final states. These decays may help confirm the existence of certain resonances. Moreover, electromagnetic decay widths provide additional information that can be particularly useful for distinguishing resonances with the same mass and total decay width. This study presents, for the first time, the calculation of electromagnetic decays for $D_{\rho }$-wave states, $\rho -\lambda$ mixed states, and $\rho$-mode radially excited states. Throughout our calculations, we account for uncertainties arising from both experimental and model-dependent errors.

We perform a holographic analysis of several quantum information-theoretic observables—entanglement entropy (EE), mutual information (MI), entanglement wedge cross section (EWCS), butterfly velocity ($v_B$), and thermo mutual information (TMI)—in the background of charged anti–de Sitter (AdS) black hole deformed by a homogeneous string cloud. This configuration is dual to a large ${\mathcal{N}}_c$ strongly coupled field theory at finite temperature and finite chemical potential, in presence of quark-cloud. We study how the entanglement structure and chaotic dynamics in the boundary theory are affected by the charge and backreaction. In our observation we find that both EE and EWCS increase monotonically with charge and backreaction, indicating enhanced correlations due to additional degrees of freedom. On the other hand MI and TMI show a more intricate dependence: backreaction tends to strengthen correlations, while increasing charge suppresses entanglement and makes the system more susceptible to scrambling. The analysis of the butterfly velocity $v_B$ indicates that the presence of charge and the backreaction suppress the chaotic behavior of the system by. Furthermore, TMI exhibits a sharp transition under shockwave perturbations, with interboundary entanglement being entirely disrupted beyond a critical shock strength, which decreases with increasing charge.