Motivated by the near-threshold enhancement and the dip structure around 1 GeV in the ${\pi }^0{\pi }^0$ invariant mass distribution of the process $D^0\to {\pi }^0{\pi }^0{\overline{K}}^0$ observed by the CLEO Collaboration, we have investigated this process by taking into account the contribution from the $S$-wave pseudoscalar meson–pseudoscalar meson interactions within the chiral unitary approach, and also the one from the intermediate resonance ${\overline{K}}^{*}(892)$. Our results are in good agreement with the CLEO measurements, which implies that the near-threshold enhancement near the ${\pi }^0{\pi }^0$ threshold is mainly due to the contributions from the scalar meson $f_0(500)$ and the intermediate ${\overline{K}}^{*}$, and the cusp structure around 1 GeV in the ${\pi }^0{\pi }^0$ invariant mass distribution should be associated with the scalar meson $f_0(980)$.

The BESIII observation of the $X(2600)$ suggests that one possible assignment for its spin-parity quantum numbers is $J^{PC}=2^{-+}$. This finding motivates us to systematically revisit isoscalar pseudotensor mesonic states through a comprehensive spectroscopic study. In this work, we employ a potential model to calculate the mass spectrum of isoscalar pseudotensor meson states with varying radial quantum numbers. Additionally, we analyze their strong decay behaviors, as allowed by the Okubo-Zweig-Iizuka rule, using the quark pair creation model. Our findings yield valuable information about their resonant parameters and partial decay widths, which can aid in identifying the observed isoscalar pseudotensor states when combined with current experimental data. Importantly, we also predict several radial excitations of isoscalar pseudotensor mesons that remain unobserved experimentally. Furthermore, we exclude the $X(2600)$ from being classified as an isoscalar pseudotensor meson, which is critical for elucidating the properties of the $X(2600)$.

We calculate the energy dependence of inclusive and diffractive neutrino-nucleus deep-inelastic scattering cross sections within the dipole picture, focusing on the ultrahigh-energy regime. We predict an up to $\sim 10\%$ nuclear suppression in the inclusive neutrino-oxygen scattering originating from the nonlinear QCD dynamics in the small-$x$ Balitsky-Kovchegov evolution. Diffraction is found to be a small $1\%-4\%$ contribution to the total cross section across a wide range of neutrino energies relevant for current and near-future experiments. The diffractive cross section is calculated separately for the coherent and incoherent channels that are found to be of equal importance. Additionally, we include the dominant contribution from the $|q\overline{q}g⟩$ Fock state of the $W^{\pm }$ and $Z$ bosons in the high-$Q^2$ limit, along with the lowest-order $|q\overline{q}⟩$ contribution. The $|q\overline{q}g⟩$ contribution is found to be numerically significant, reaching up to 40% of the diffractive cross section.

Based upon a combined formalism of Schwinger-Dyson and Bethe-Salpeter equations in quantum chromodynamics (QCD), we propose a QCD-kindred algebraic model for the dressed quark propagator, for the Bethe-Salpeter amplitude of the pion and the electromagnetic quark-photon interaction vertex. We then compute the ${\gamma }^{*}{\pi }^0\gamma$ transition form factor $G^{{\gamma }^{*}{\pi }^0\gamma }(Q^2)$ for a wide range of photon momentum transfer squared $Q^2$. The quark propagator is expanded out in its perturbative functional form but with dynamically generated dressed quark mass. It has complex conjugate pole singularities in the complex-momentum plane, which is motivated by the solution of the quark gap equation with rainbow-ladder truncation of the infinite set of Schwinger-Dyson equations. This complex pole singularity structure of the quark propagator can be associated with a signal of confinement, which prevents quarks from becoming stable asymptotic states. The Bethe-Salpeter amplitude is expressed without a spectral density function, which encapsulates its low- and large-momentum behavior. The QCD evolution of the distribution amplitude is also incorporated into our model through the direct implementation of Efremov-Radyushkin-Brodsky-Lepage evolution equations. We include the effects of the quark anomalous magnetic moment in the description of the quark-photon vertex, whose infrared enhancement is known to dictate hadronic properties. Once the QCD-kindred model is constructed, we calculate the form factor $G^{{\gamma }^{*}{\pi }^0\gamma }(Q^2)$ and find it consistent with direct QCD-based studies, as well as most available experimental data. It slightly exceeds the conformal limit for large $Q^2$, which might be attributed to the scaling violations in QCD. The associated interaction radius and neutral pion decay width turn out to be compatible with experimental data.

We investigate two-pion emission decays of singly charmed and bottom baryons, focusing on ${\mathrm{\Lambda }}_Q^{*}(1P)$ and ${\mathrm{\Xi }}_Q^{*}(1P)$ states with $J^P=1/2^{-}$ and $3/2^{-}$, which belong to the flavor triplet ${\overline{\mathbf{3}}}_F$. Our study includes both sequential decays through intermediate states in the flavor sextet ${\mathbf{6}}_F$ and direct three-body decay, with coupling constants estimated using the chiral quark model and chiral-partner scheme. Examining recent Belle measurements for ${\mathrm{\Lambda }}_c(2625{)}^{+}$, we confirm its assignment as a $\lambda$-mode excitation with $J^P=3/2^{-}$. We then give predictions for other cases, including the ${\mathrm{\Xi }}_Q^{*}$ decays. The observed asymmetry in the $\pi \pi$ mass distribution highlights the role of the direct process, reflecting the chiral-partner structure. However, the direct process is less significant in three-body decays unless $S$-wave resonances are suppressed. Further experiments are needed to test our predictions and get more insights into the structure of heavy baryons.

We calculate the gravitational tensor-monopole moment of the momentum-current density $T^{ij}$ in the ground state of the hydrogen atom to order $\mathcal{O}(\alpha )$ in quantum electrodynamics (QED). The result is ${\tau }_H/{\tau }_0-1=\frac{4\alpha }{3\pi }(\ln {\alpha }^2-0.028)=-3.06\times {10}^{-2}$ where ${\tau }_0={\hslash }^2/4m_e$ is the leading-order moment. The physics of the next-to-leading-order correction is similar to that of the famous Lamb shift for energy levels.

By investigating the soft gluon radiation in the $J/\psi$ plus jet photoproduction at the electron-ion collider (EIC), we demonstrate that the azimuthal angular correlations between the leading jet and heavy quarkonium provide a unique probe to the production mechanism of the latter. In particular, a significant $\cos (\varphi )$ asymmetry is found for the color-singlet channel, whereas it vanishes or has an opposite sign for color-octet production, depending on the jet transverse momentum. Numerical results of $\cos (\varphi )$ and $\cos (2\varphi )$ asymmetries employing both the color-singlet model and the nonrelativistic QCD approach are presented for typical kinematics at the future EIC.

We study Higgs boson production at ${\mu }^{+}{\mu }^{+}$ colliders at high energy. Since both initial-state particles are positively charged, there is no $W$ boson fusion at the leading order, as it requires a $W^{+}{W}^{-}$ pair. However, we find that the cross section of the higher-order, $\gamma$-and $Z$-mediated $W$ boson fusion process is large at high center-of-mass energies $\sqrt{s}$, growing as $(\log s{)}^3$. This is in contrast to the $\log s$ behavior of the leading-order $W$ boson fusion. Thus, even though it is a higher-order process, the rate of Higgs boson production for 10 TeV energies at ${\mu }^{+}{\mu }^{+}$ colliders with polarized beams can be as high as about half of the one at ${\mu }^{+}{\mu }^{-}$ colliders, assuming the same integrated luminosity. To calculate the cross section of this process accurately, we carefully treat the collinear emission of the photon in the intermediate state. The thereby obtained large cross section furthermore shows the significance of Higgs production with an extra $W$ boson in the final state also at ${\mu }^{+}{\mu }^{-}$ and $e^{+}{e}^{-}$ colliders.

We present a study of the semileptonic decay $D^0\to {\pi }^{-}{\pi }^0{e}^{+}{\nu }_e$ using an $e^{+}{e}^{-}$ annihilation data sample of $7.93{\mathrm{fb}}^{-1}$ collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. The branching fraction of $D^0\to \rho (770{)}^{-}{e}^{+}{\nu }_e$ is measured to be $(1.439\pm 0.033(\mathrm{stat})\pm 0.027(\mathrm{syst}))\times {10}^{-3}$, which is a factor 1.6 more precise than previous measurements. By performing an amplitude analysis, we measure the hadronic form-factor ratios of $D^0\to \rho (770{)}^{-}{e}^{+}{\nu }_e$ at $q^2=0$ assuming the single-pole-dominance parametrization: $r_V=V(0)/A_1(0)=1.548\pm 0.079(\mathrm{stat})\pm 0.041(\mathrm{syst})$ and $r_2=A_2(0)/A_1(0)=0.823\pm 0.056(\mathrm{stat})\pm 0.026(\mathrm{syst})$.

The China Jinping underground Laboratory (CJPL) is an excellent location for studying solar, terrestrial, and supernova neutrinos due to its 2400-meter vertical rock overburden. Its unparalleled depth gives an opportunity to investigate the cosmic-ray muons with exceptionally high average energy at $\sim 360\mathrm{GeV}$. This paper details a study of muon-related backgrounds based on 1178 days of data collected by the 1-ton prototype neutrino detector used for the Jinping Neutrino Experiment (JNE) since 2017. The apparent effects for the leakage of muons’ secondary particles due to detector’s finite size on the measured neutron yield are first discussed in detail. The analysis of 493 cosmic-ray muon candidates and $13.6\pm 5.7$ cosmogenic neutron candidates, along with a thorough evaluation of detection efficiency and uncertainties, gives a muon flux of $(3.56\pm {0.16}_{\mathrm{stat}}\pm {0.10}_{\mathrm{syst}})\times {10}^{-10}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ and a cosmogenic neutron yield of $(3.37\pm 1.41_{\mathrm{stat}}\pm 0.31_{\mathrm{syst}})\times {10}^{-4}{\mathrm{\mu }}^{-1}{\mathrm{g}}^{-1}{\mathrm{cm}}^2$ in LAB-based liquid scintillator.

Measurements of the polarization and spin correlation in top quark pairs ($t\overline{t}$) are presented using events with a single electron or muon and jets in the final state. The measurements are based on proton-proton collision data from the LHC at $\sqrt{s}=13\mathrm{TeV}$ collected by the CMS experiment, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. All coefficients of the polarization vectors and the spin correlation matrix are extracted simultaneously by performing a binned likelihood fit to the data. The measurement is performed inclusively and in bins of additional observables, such as the mass of the $t\overline{t}$ system and the top quark scattering angle in the $t\overline{t}$ rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the $t\overline{t}$ spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for $t\overline{t}$ states at the production threshold and at high masses of the $t\overline{t}$ system. Entanglement is observed for the first time in events at high $t\overline{t}$ mass, where a large fraction of the $t\overline{t}$ decays are spacelike separated, with an expected and observed significance of above 5 standard deviations.

A search for dark sectors is performed using the unique M2 beam line at the CERN Super Proton Synchrotron. New particles ($X$) could be produced in the bremsstrahlung-like reaction of high-energy 160 GeV positively charged muons impinging on an active target, $\mu N\to \mu NX$, followed by their decays, $X\to \text{invisible}$. The experimental signature would be a scattered single muon from the target, with about less than half of its initial energy and no activity in the subdetectors located downstream from the interaction point. The full sample of the 2022 run is analyzed through the missing-energy/momentum channel, with total statistics of $(1.98\pm 0.02)\times {10}^{10}$ muons on target. We demonstrate that various muonphilic scenarios involving different types of mediators, such as scalar or vector particles, can be probed simultaneously with such a technique. For the vector case, besides a $L_{\mu }-L_{\tau }$ $Z^{\prime }$ vector boson, we also consider an invisibly decaying dark photon ($A^{\prime }\to \text{invisible}$). This search is complementary to NA64 running with electrons and positrons, thus opening the possibility to expand the exploration of the thermal light dark matter parameter space by combining the results obtained with the three beams.

Two fundamental signatures of quantum field theory are tunneling and the Casimir effect. We examine the ground state energetic properties of a scalar field confined on a $D$-dimensional sphere and subjected to these two effects. We focus on $D=2$ and $D=3$, with a negative coupling of a massless scalar field to curvature, providing a radius-dependent effective mass that triggers symmetry breaking. This scenario allows tunneling to be more important than the Casimir effect, in a certain regime of parameters, and potential implications in early cosmology are discussed for the case $D=3$, which could avoid a cosmological singularity.

A typical example of superintegrability is provided by expression of the Hopf link hyperpolynomial in an arbitrary representation through a pair of the Macdonald polynomials at special points. In the simpler case of the Hopf link HOMFLY-PT polynomial and a pair of the Schur functions, it is a relation in the unitary matrix model. We explain that the Cherednik-Mehta-Macdonald identity for bilinear Macdonald residues with an elliptic weight function is nothing but a reformulation of these same formulas. Their lifting to arbitrary knots and links, even torus ones, remains obscure.

The frozen star model describes a type of black hole mimicker; that is, a regular, horizonless, ultracompact object that behaves just like a Schwarzschild black hole from an external-observer’s perspective. In particular, the frozen star is bald, meaning that it cannot be excited. To mimic the possible excitations of the frozen star, it needs to be “defrosted” by allowing deviations from the maximally negative radial pressure and vanishing tangential pressure of the fluid sourcing the star. Here, we extend a previous study on nonradial oscillations of the defrosted star by considering, in addition to the fluid modes, the even-parity metric perturbations and their coupling to the fluid modes. At first, general equations are obtained for the perturbations of the energy density and pressure along with the even-parity perturbations of the metric for a static, spherically symmetric but otherwise generic background with an anisotropic fluid. This formal framework is then applied to the case of a defrosted star. The spectrum of nonradial oscillations is obtained to leading order in an expansion in terms of $\gamma$, which is the small relative deviation away from maximally negative radial pressure. We find that the sound velocity of the modes is nonrelativistic, and proportional to $\gamma$, while their lifetime is parametrically long, proportional to $1/{\gamma }^2$. This result was anticipated by previous discussions on the collapsed polymer model, whose strongly nonclassical interior is argued to provide a microscopic description of the frozen and defrosted star geometries. Our results will serve as a starting point for calculating the spectrum of emitted gravitational waves from an excited frozen star.

In this work, we investigate tidal forces in the Lemaitre-Tolman-Bondi (LTB) metric, focusing on both hidden and locally visible singularities. We discuss the strength of these singularities in terms of deformationally strong singularities. Specifically, we analyze tidal forces in LTB spacetime, calculating radial and angular tidal forces and Jacobi fields for the radially comoving shell. To provide a comparative study, we consider both homogeneous and inhomogeneous cases. The matter field distribution at one-time slice can differ significantly from another, highlighting the potential for time-dependent tidal deformation as a distinct observational signature. We focus on a specific feature: the time-varying maximum of stretching in the radial tidal force, which we term the “critical tidal boundary.” In the inhomogeneous case, close to singularity time ($t<t_s$), the magnitudes of tidal forces vary substantially, with significant differences in compressive and stretching forces within a small physical radius $R(t,r)$. The resulting singularity in the LTB metrics at the end state of gravitational collapse appears to be an Ori-strong singularity, characterized by infinite tidal deformation.

We study Hawking radiation and wave scattering of charged scalar fields in a charged $C$-metric black hole background. The conformally invariant wave equation for charged scalar fields can be separated into radial and angular parts, each with five singularities. We first show that the radial and angular equations can be respectively transformed into the general Heun equation, and then we explore exact solutions of the radial Heun equation in terms of the local Heun functions and connection coefficients. Exact behaviors of the asymptotic wave functions are determined without approximations. We further apply the exact results to derive Hawking radiation, quasinormal modes, and superradiance.

Characterization of search selection effects comprises a core element of gravitational-wave data analysis. Knowledge of selection effects is needed to predict observational prospects for future surveys and is essential in the statistical inference of astrophysical source populations from observed catalogs of compact binary mergers. Although gravitational-wave selection functions can be directly measured via injection campaigns—the insertion and attempted recovery of simulated signals added to real instrumental data—such efforts are computationally expensive. Moreover, the inability to interpolate between discrete injections limits the ability to which we can study narrow or discontinuous features in the astrophysical distribution of compact binary properties. For this reason, there is a growing need for alternative representations of gravitational-wave selection functions that are computationally cheap to evaluate and can be computed across a continuous range of compact binary parameters. In this paper, we describe one such representation. Using pipeline injections performed during Advanced LIGO and Advanced Virgo’s third observing run (O3), we train a neural network emulator for $P(\det |\theta )$, the probability that a given compact binary with parameters is successfully detected, averaged over the course of O3. The emulator captures the dependence of $P(\det |\theta )$ on binary masses, spins, distance, sky position, and orbital orientation, and it is valid for compact binaries with component masses between 1 and $100M_{\odot }$. We test the emulator’s ability to produce accurate distributions of detectable events, and demonstrate its use in hierarchical inference of the binary black hole population.

We present a proof-of-principle implementation of the first fully covariant filtering scheme applied to relativistic fluid turbulence. The filtering is performed with respect to special observers, identified dynamically as moving with the “bulk of the flow.” This means that filtering does not depend on foliations of spacetime but rather on the intrinsic fibration traced out by the observers. The covariance of the approach means that the results may be lifted into an arbitrary, curved spacetime. This practical step follows theoretical work showing that the residuals introduced by filtering a fine-scale ideal fluid can be represented by a nonideal fluid prescription at the coarse scale. We interpret such nonideal terms using a simple first-order gradient model, which allows us to extract effective turbulent viscosities and conductivity. A statistical regression on these terms shows that the majority of their variation may be explained by the thermodynamic properties of the filtered fluid and invariants of its flow, such as the shear and vorticity. This serves as a validation of the method and enables us to fit a functional, power-law form for the nonideal coefficients—an approach that may be used practically to give a subgrid closure model in large-eddy simulations.

Nonlinear simulations of neutron star mergers are complicated by the need to represent turbulent dynamics. As we cannot (yet) perform simulations that resolve accurately both the gravitational-wave scale and the smallest scales at which magneto/hydrodynamic turbulence plays a role, we need to rely on approximations. Addressing this problem in the context of large-eddy models, we outline a coherent Lagrangian filtering framework that allows us to explore the many issues that arise, linking conceptual problems to practical implementations and the interpretation of the results. We develop understanding crucial for quantifying unavoidable uncertainties in current and future numerical relativity simulations and consider the implications for neutron-star parameter estimation and constraints on the equation of state of matter under extreme conditions.