The decay behavior of an exotic state can be used to probe its internal structure. We note that the hidden-charm pentaquark states, $P_{\psi }^N(4312)$, $P_{\psi }^N(4440)$, and $P_{\psi }^N(4457)$, have only been observed in the $J/\psi p$ channel. In this work, we employ the effective Lagrangian approach to systematically investigate the two-body and three-body decays of the heavy quark spin symmetry multiplet of hadronic molecules ${\overline{D}}^{(*)}{\mathrm{\Sigma }}_c^{(*)}$. Our results show that the partial decay widths of the hidden-charm pentaquark molecules into ${\overline{D}}^{(*)}{\mathrm{\Lambda }}_c\pi$ are sizable so that ${\overline{D}}^{(*)}{\mathrm{\Lambda }}_c\pi$ are promising channels to search for them, which can help clarify their molecular nature.

The multipole moments of the $J^P=3^{-}$ tensor mesons are obtained using light-cone sum rules. Our results are compared with the predictions of the light-cone helicity formalism within the framework of SU(3) flavor symmetry. We observe a good agreement between the two approaches. The obtained multipole moments of tensor mesons provide deeper insights into their properties and better understanding of the strong and electromagnetic decay channels of these mesons.

Inspired by the newly observed $X(2085)$ by the BESIII Collaboration, we study the strong decay behaviors of excited axial-vector strange mesons within the quark pair creation model. Our results indicate that the $K_1(1793)/K_1(1861)$ can be regarded as the same $K_1(2P)$ state, and the $K_1(1911)$ is assigned as the $K_1(2P^{\prime })$ state. Considering the mass, spin-parity, and decay behaviors, we interpret the newly observed $X(2085)$ as the radially excited $K_1(3P)$ state, which mainly decays into the $K^{*}(1410)\pi$, $\rho K^{*}$, $\omega (1420)K$, $\rho (1450)K$, and $\rho K$ final states. Also, the width of the $K_1(3P^{\prime })$ state is predicted to be about 300 MeV, which can be searched for by future experiments. We expect that present calculations can help us to better understand the nature of the $X(2085)$ structure and near-threshold enhancements in the baryon-antibaryon invariant mass distributions.

A search for proton decay into $e^{+}/{\mu }^{+}$ and a $\eta$ meson has been performed using data from a $0.373\mathrm{Mton}·\mathrm{year}$ exposure (6050.3 live days) of Super-Kamiokande. Compared to previous searches this work introduces an improved model of the intranuclear $\eta$ interaction cross section, resulting in a factor of 2 reduction in uncertainties from this source and $\sim 10\%$ increase in signal efficiency. No significant data excess was found above the expected number of atmospheric neutrino background events resulting in no indication of proton decay into either mode. Lower limits on the proton partial lifetime of $1.4\times {10}^{34}\mathrm{years}$ for $p\to e^{+}\eta$ and $7.3\times {10}^{33}\mathrm{years}$ for $p\to {\mu }^{+}\eta$ at the 90% CL were set. These limits are around 1.5 times longer than our previous study and are the most stringent to date.

The quasinormal mode spectrum of black holes plays a crucial role in the modeling of postmerger ringdown signals. However, the spectrum is extremely sensitive to small deformations of the system and describes the linear response only in a certain (not precisely defined) time frame after the merger. We argue here that the graybody factors, recently shown to describe the ringdown spectral amplitude at relatively high frequencies, are instead stable under small perturbations of the system and free of certain ambiguities that plague the quasinormal mode spectrum. Our analysis also unveils a nontrivial interplay: While certain ringdown quantities are dominated by the contribution of spectrally unstable quasinormal modes, these modes conspire to produce stable observables. Thus, we propose a complementary approach to ringdown studies, which circumvents some limitations of the standard quasinormal mode description.

We examine the phenomenon of electron-positron pair production from vacuum in a combination of two counterpropagating electromagnetic pulses having a duration of the order of the Compton time. We show that in this extreme short-time domain, the momentum distributions of the particles produced possess a peculiar structure which strongly depends on whether the electromagnetic pulses have a unipolar or bipolar profile. It is shown that bipolar pulses can predominantly generate particles with ultrarelativistic velocities along the propagation direction of the pulses, while unipolar ones are generally more favorable in terms of the total particle yield in the same regime. The highly nontrivial properties of the $e^{+}{e}^{-}$ spectra revealed in our study provide strong experimental signatures paving the way to probe a complex vacuum response within the short-time domain of quantum electrodynamics.

We investigate the curved-spacetime dynamics of charged spin-$\frac{1}{2}$ particles minimally coupled to the electromagnetic field and propagating in superposed states of different masses. For that purpose, we make use of a Wentzel-Kramers-Brillouin approximation of the Dirac equation with a minimal coupling to the Maxwell field in curved spacetime. We obtain the spin dynamics as well as the deviation from geodesic motion of such particles. The problem of having the mass eigenstates experience different proper times, as opposed to the case of neutral particles, is here dealt with by first extracting the second-order differential equation obeyed by each superposition. This strategy proves to be not only powerful, but also very economical.

A class of globally scale-invariant scalar-tensor theories have been proposed to be invariant under a larger class of transformations that take the form of local Weyl transformations supplemented by a restriction that the conformal factor satisfies a covariant Klein-Gordon equation. The action of these theories indeed seems to be invariant under such transformations up to boundary terms, this property being referred to as “restricted Weyl symmetry.” However, we find that corresponding equations of motion are not invariant under these transformations. This is a paradox, that is explained by realizing that the restriction condition on the conformal factor forces the restricted Weyl transformation to be a nonlocal transformation. For nonlocal transformations would-be boundary terms cannot in general be discarded from the action. Moreover, variations of trajectories cannot be assumed to vanish at boundaries of the action when deriving equations of motion. We illustrate both of these less known properties by considering a series of simple examples. Finally, we apply these observations to the case of globally scale-invariant scalar-tensor theories to demonstrate that restricted Weyl transformations are, in fact, not symmetries of the full system.

Gravitational-wave memory is characterized by a signal component that persists after a transient signal has decayed. Treating such signals in the frequency domain is nontrivial, since discrete Fourier transforms assume periodic signals on finite time intervals. In order to reduce artifacts in the Fourier transform, it is common to use recipes that involve windowing and padding with constant values. Here, we discuss how to regularize the Fourier transform in a straightforward way by splitting the signal into a given sigmoid function that can be Fourier transformed in closed form and a residual which does depend on the details of the gravitational-wave signal and has to be Fourier transformed numerically but does not contain a persistent component. We provide a detailed discussion of how to map between continuous and discrete Fourier transforms of signals that contain a persistent component. We apply this approach to discuss the frequency-domain phenomenology of the $(\ell =2,m=0)$ spherical harmonic mode, which contains both a memory and an oscillatory ringdown component.

The merging of two black holes is a notoriously difficult process to describe exactly. Nevertheless, the hindrances posed by gravity’s nonlinearity can be circumvented by focusing on the strict extreme mass ratio limit, in which one of the black holes is infinitely larger than the other. Such an approach has been developed by Emparan and Martínez and applied within general relativity to investigate the time evolution of event horizons melding, using nothing but elementary concepts in gravitational physics and simple integrations of geodesics. We apply this strategy to study black hole mergers in higher derivative gravity in order to assess how the defining characteristics of the fusion process change as the gravitational theory is modified. We adopt the case of Einsteinian cubic gravity for concreteness, and determine how the mergers’ duration and the relative area increment change as the theory’s single coupling parameter is varied.

Recent studies have shown that orbital eccentricity may indicate dynamical assembly as a formation mechanism for binary black holes. Eccentricity leaves a distinct signature in gravitational wave signals and it may be measured if the binary remains eccentric when it enters the LIGO band. Although eccentricity has not yet been confidently detected, the possibility of detecting eccentric binaries is becoming more likely with the improved sensitivity of gravitational wave detectors such as LIGO, Virgo, and KAGRA. It is crucial to assess the accuracy of current search pipelines in recovering eccentricity from gravitational wave signals if it is present. In this study, we investigate the ability of parameter estimation pipeline RIFT to recover eccentricity in the nonspinning and aligned-spin cases for low mass binary black holes. We use TaylorF2Ecc and TEOBResumS to inject sets of synthetic signals and test how well RIFT accurately recovers key binary black hole parameters. Our findings provide valuable insights into the capability of current parameter estimation methods to detect and measure eccentricity in gravitational wave signals.

We nonparametrically reconstruct the late-time expansion history in light of the latest baryon acoustic oscillation (BAO) measurements from DESI combined with various type Ia supernovae (SNeIa) catalogs, using interpolation through piece-wise natural cubic splines, and a reconstruction procedure based on Gaussian processes (GPs). Applied to DESI BAO and PantheonPlus SNeIa data, both methods indicate that deviations from a reference $\mathrm{\Lambda }\mathrm{CDM}$ model in the $z\lesssim 2$ unnormalized expansion rate $E(z)$ are constrained to be $\lesssim 10\%$, but also consistently identify two features in $E(z)$: a bump at $z\sim 0.5$, and a depression at $z\sim 0.9$, which cannot be simultaneously captured by a $w_0{w}_a\mathrm{CDM}$ fit. These features, which are stable against assumptions regarding spatial curvature, interpolation knots, and GP kernel, disappear if one adopts the older SDSS BAO measurements in place of DESI, and decrease in significance when replacing the PantheonPlus catalog with the Union3 and DESY5 ones. We infer $c/(r_d{H}_0)=29.90\pm 0.33$, with $r_d$ the sound horizon at baryon drag and $H_0$ the Hubble constant. Breaking the $r_d-H_0$ degeneracy with the SH0ES prior on $H_0$, the significance of the tension between our nonparametric determination of $r_d=136.20_{-2.40}^{+2.20}\mathrm{Mpc}$ and the Planck $\mathrm{\Lambda }\mathrm{CDM}$-based determination is at the $5\sigma$ level, slightly lower than the $6\sigma$ obtained when adopting the older SDSS dataset in place of DESI. This indicates the persistence at very high significance of the “sound horizon tension,” reinforcing the need for prerecombination new physics. If substantiated in forthcoming data releases, our results tentatively point to oscillatory/nonmonotonic features in the shape of the expansion rate at $z\lesssim 2$, of potential interest for dark energy model-building.

We present an up-to-date compilation of published Hubble constant ($H_0$) measurements that are independent of the cosmic microwave background sound horizon scale. This compilation is split in two distinct groups: A. Distance ladder measurements sample comprising of 20 recent measurements, primarily from the past four years, utilizing various rung 2 calibrators and rung 3 cosmic distance indicators. B. One-step measurements sample including 33 measurements of $H_0$ that are independent of both the cosmic microwave background sound horizon scale and the distance ladder approach. These 33 measurements are derived from diverse probes such as cosmic chronometers, gamma-ray attenuation, strong lensing, megamasers etc. Statistical analysis reveals a significant distinction between the two samples. The distance ladder-based sample yields a best fit $H_0=72.8\pm 0.5\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ with ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=0.51$ indicating some correlations. The one-step measurements result in $H_0=69.0\pm 0.48\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ with ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=1.37$ indicating some internal tension. If two outlier measurements are removed (TDCOSMO.I-2019 known to have systematics and MCP-2020), then the best fit of the one-step sample reduces to $H_0=68.3\pm 0.5\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ with ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=0.95$, fully self-consistent and consistent with sound horizon based measurements. An alternative, restricted subsample of the one-step measurements with correlated measurements removed, leads to a best fit $H_0=68.5\pm 0.8\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ with ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=1.08$ demonstrating the robustness of our results. These findings suggest that the core of the Hubble tension lies not between early and late-time measurements, but between distance ladder measurements and all other $H_0$ determinations. These findings suggest that understanding the origin of the Hubble tension requires careful investigation of both possible systematic effects and potential new physics affecting cosmic distance ladder measurements.

We train neural networks to quickly generate redshift-space galaxy power spectrum covariances from a given parameter set (cosmology and galaxy bias). This covariance emulator utilizes a combination of traditional fully connected network layers and transformer architecture to accurately predict covariance matrices for the high redshift, north galactic cap sample of the BOSS DR12 galaxy catalog. We run simulated likelihood analyses with emulated and brute-force computed covariances, and we quantify the network’s performance via two different metrics: (1) difference in ${\chi }^2$ and (2) likelihood contours for simulated BOSS DR 12 analyses. We find that the emulator returns excellent results over a large parameter range. We then use our emulator to perform a reanalysis of the BOSS HighZ NGC galaxy power spectrum, and find that varying covariance with cosmology along with the model vector produces ${\mathrm{\Omega }}_m=0.276_{-0.015}^{+0.013}$, $H_0=70.2\pm 1.9\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, and ${\sigma }_8=0.674_{-0.077}^{+0.058}$. These constraints represent an average $0.46\sigma$ shift in best-fit values and a 5% increase in constraining power compared to fixing the covariance matrix (${\mathrm{\Omega }}_m=0.293\pm 0.017$, $H_0=70.3\pm 2.0\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, ${\sigma }_8=0.702_{-0.075}^{+0.063}$). This work demonstrates that emulators for more complex cosmological quantities than second-order statistics can be trained over a wide parameter range at sufficiently high accuracy to be implemented in realistic likelihood analyses.

We propose and implement a novel test to assess deviations from well-established concordance $\mathrm{\Lambda }\mathrm{CDM}$ cosmology while inferring dark energy properties. In contrast to the commonly implemented parametric forms of the dark energy equation-of-state (EoS), we test the validity of the cosmological constant on the more fundamental scale factor [$a(t)$] which determines the expansion rate of the Universe. We constrain our extended “general model” using the late-time observables. The posterior of the dark energy EoS is mainly constrained to be quintessencelike naturally excluding physically unviable regions such as phantom crossings or exponential growth.

Spatially homogeneous thermal equilibria of self-gravitating gas, being impossible otherwise, are nevertheless allowed in an expanding background accounting for a universe’s expansion. Furthermore, a fixed density at the boundary of a perturbation is a natural boundary condition keeping the mass finite inside without the need to invoke any unphysical walls. These facts allow us to develop a consistent gravitational thermodynamics of isothermal spheres inside an expanding universe. In the canonical and grand canonical ensembles we identify an instability for both homogeneous and inhomogeneous equilibria. We discuss a potential astrophysical application. If such an instability is triggered on baryonic gas at high redshift $z>137$ when the primary baryonic component, namely atomic hydrogen, was still thermally locked to the cosmic microwave background radiation, then the corresponding destabilized gaseous clouds have baryonic mass $\ge 0.8\times {10}^5{M}_{\odot }$ and radius $\ge 15\mathrm{pc}$.

Rotating fermion-boson stars are hypothetical celestial objects that consist of both fermionic and bosonic matter interacting exclusively through gravity. Bosonic fields are believed to arise in certain models of particle physics describing dark matter and could accumulate within neutron stars, modifying some of their properties and gravitational wave emission. Fermion-boson stars have been extensively studied in the static nonrotating case, exploring their combined stability and their gravitational radiation in binary mergers. However, stationary rotating configurations were yet to be found and investigated. The presence of a bosonic component could impact the development of the bar-mode instability in differentially rotating neutron stars. Therefore, the study of rotating fermion-boson stars has important implications for astrophysics, as they could provide a new avenue for the detection of gravitational waves. In addition, these objects may shed light on the behavior of matter under extreme conditions, such as those found in the cores of neutron stars, and explain any tension in the determination of the dense-matter equation of state from multimessenger observations. In this work we study a new consistent method of constructing uniformly rotating fermion-boson stars, and we analyze some of their main properties. These objects might offer alternative explanations for current observations populating the lower black hole mass gap, as the $2.6M_{\odot }$ compact object involved in GW190814.

We introduce the concept of the quark quasifragmentation function (qFF) using an equal-time and spatially boosted form of the Collins-Soper fragmentation function where the out-meson fragment is replaced by the current asymptotic condition. We derive the qFF for a fermion in two-dimensional quantum electrodynamics (QED2) using the Kogut-Susskind Hamiltonian after a mapping onto spin qubits in a spatial lattice with open boundary conditions. This form is suitable for quantum computations. We compute the qFF by exact diagonalization of the spin Hamiltonian. The results are compared to the qFF following from the Drell-Levy-Yan result for QED2, both at strong and weak coupling, and to two-dimensional quantum chromodynamics in the lowest Fock approximation.

We perform a nonperturbative lattice study of the electroweak phase transition in the real singlet scalar extension of the Standard Model. We consider both the heavy and light singletlike scalar regimes at nonzero singlet-doublet mixing angle. After reviewing features of the lattice method relevant for phase transition studies, we analyze the dependence of phase transition thermodynamics on phenomenologically relevant parameters. In the heavy singletlike scalar regime, we find that the transition is a crossover for small doublet-singlet mixing angles, despite the presence of an energy barrier in the tree-level potential. The transition becomes first order for sufficiently large mixing angles. We find two-loop perturbation theory to agree closely with the lattice results for all thermodynamical quantities considered here (critical temperature, order parameter discontinuity, latent heat) when the transition is strongly first order. For the light singletlike scalar regime relevant to exotic Higgs decays, we update previous one-loop perturbative results using the two-loop loop dimensionally reduced effective field theory and assess the nature of the transition with lattice simulations at set of benchmark parameter points. For fixed singletlike scalar mass the transition becomes crossover when the magnitude of the Higgs-singlet portal coupling is small. We perform our simulations in the high-temperature effective theory, which we briefly review, and present analytic expressions for the relevant lattice-continuum relations.