We introduce a class of relativistic fluid states satisfying the relativistic local thermodynamical equilibrium postulate [abbreviated as relativistic (LTE) postulate]. States satisfying this postulate are states “near equilibrium” (a term defined precisely in the course of the paper), and, they permit one to attach a fictitious “local thermodynamical equilibrium” state that fits event by event the actual fluid state. States within this class allow one to single out an admissible class of rest frames relative to which thermodynamical variables like the energy density, thermodynamical pressure, stresses, and particle number density (or densities) measured by observers at rest relative to these frames are becoming frame independent provided second (or higher) order deviations from the fictitious state of local thermodynamical equilibrium are ignored. We have verified this property for a large class of theories of relativistic dissipation that include the Hiscock-Lindblom class of first-order theories, the Eckart and Landau-Lifshitz theories, the Israel-Stewart transient thermodynamics, the Liu-Müller-Ruggeri theory, fluids of divergence type, and the latest developed (BDNK) theory. Moreover, for states that are compatible with the relativistic (LTE) postulate, we show that the phenomenological equations describing first-order deviations from any fictitious local thermodynamical equilibrium state satisfy equations that remain form invariant under change of frame within the admissible class of frames. We proved this property for the Hiscock-Lindblom class of first-order theories, the Eckart and Landau-Lifshitz theories, the Israel-Stewart transient thermodynamics, the Liu-Müller-Ruggeri theory of relativistic dissipation, and the (BDNK) theory, and we expect the same property to hold for the class of relativistic fluids of divergence type.

We investigate the timescale on which quantum corrections alter the predictions of classical field theory for scalar field dark matter. This is accomplished by including second-order terms in the evolution proportional to the covariance of the field operators. When this covariance is no longer small compared to the mean field value, we say that the system has reached the “quantum breaktime,” and the predictions of classical field theory will begin to differ from those of the full quantum theory. While holding the classical field theory evolution fixed, we determine the change of the quantum breaktime as the total occupation number is increased. This provides a novel numerical estimation of the breaktime based at high occupations $n_{\mathrm{tot}}$ and mode number $N=256$. We study the collapse of a sinusoidal overdensity in a single spatial dimension. We find that the breaktime scales as $\log (n_{\mathrm{tot}})$ prior to shell crossing and then as a power law following the collapse. If we assume that the collapsing phase is representative of halos undergoing nonlinear growth, this implies that the quantum breaktime of typical systems may be as large as $\sim 30$ of dynamical times even at occupations of $n_{\mathrm{tot}}\sim {10}^{100}$.

We assess the capabilities of a ground-based gamma-ray observatory to detect astrophysical neutrinos with energies in the 100 TeV to 100 PeV range. The identification of these events is done through the measurement of very inclined extensive air showers induced by downward-going and upward-going neutrinos. The discrimination of neutrino-induced showers in the overwhelming cosmic-ray background is achieved by analyzing the balance of the total electromagnetic and muonic signals of the shower at the ground. We demonstrate that a ${\mathrm{km}}^2$-scale wide-field-of-view ground-based gamma-ray observatory could detect a couple of very-high- to ultrahigh-energy neutrino events per year with a reasonable pointing accuracy, making it an interesting facility for multimessenger studies with both photons and neutrinos.

Higher-order effects of $CPT$ and Lorentz violation within the Standard-Model Extension effective framework including Myers-Pospelov dimension-five operator terms are studied. The model is canonically quantized by giving special attention to the arising of indefinite-metric states or ghosts in an indefinite Fock space. As is well-known, without a perturbative treatment that avoids the propagation of ghost modes or any other approximation, one has to face the question of whether unitarity and microcausality are preserved. In this work, we study both possible issues. We found that microcausality is preserved due to the cancellation of residues occurring in pairs or conjugate pairs when they become complex. Also, by using the Lee-Wick prescription, we prove that the $S$ matrix can be defined as perturbatively unitary for tree-level $2\to 2$ processes with an internal fermion line.

Flavor-changing neutral current (FCNC) top-quark decays are highly suppressed due to the Glashow-Iliopoulos-Maiani mechanism in the standard model (SM). If $t\to qh,qV$ with $V=g$, $\gamma$, $Z$ are all induced via quantum loop levels, then we investigate the effect that can enhance the top-FCNC up to the sensitivity designed at the high-luminosity (HL) LHC. Inspired by the mechanism of the scotogenic neutrino mass, we extend the SM by including $Z_2$-odd colored fermions when a $Z_2$ discrete is imposed. The results show that by taking $\mathrm{BR}(t\to ug)\lesssim 0.61\times {10}^{-4}$ recently measured by ATLAS as an input, $t\to q\gamma$ can be indirectly bounded to be $\mathrm{BR}(t\to q\gamma )\lesssim 3.2\times {10}^{-6}$, which is below the expected sensitivity at the HL LHC. After taking potential constraints from various experiments into account, the obtained branching ratios for the loop-induced $t\to qh$ and $t\to qZ$ decays can be $O({10}^{-4})$, which falls within the sensitivity at the HL LHC.

We investigate the inclusive and semi-inclusive productions of spin-$3/2$ hadrons, such as $\mathrm{\Omega }$, in unpolarized $e^{+}{e}^{-}$ annihilation. The general differential cross sections are expressed in terms of structure functions in accordance to the polarization of the hadron and the azimuthal modulations. We derive a complete definition of quark transverse momentum dependent (TMD) fragmentation functions (FFs) to spin-$3/2$ hadrons for the first time from the decomposition of the quark-quark correlation matrix at leading twist, 14 of which are newly defined corresponding to rank-3 tensor polarized hadron. The collinear FFs are obtained from the $k_T$-integrated correlation matrix, and only two TMD FFs with rank-3 tensor polarization have nonvanishing collinear counterparts. Then we perform a leading order calculation of the unpolarized differential cross sections. In the single-hadron inclusive production, only two structure functions are found nonzero and none of the rank-3 tensor polarized FFs contributes. For the nearly back-to-back two-hadron production, half of the 48 structure functions are found nonzero even if the spin of the second hadron is not analyzed, and ten of the rank-3 tensor polarized TMD FFs contribute. Therefore, one can study the rank-3 tensor polarized FFs via the production of a spin-$3/2$ hadron and an unpolarized hadron in unpolarized $e^{+}{e}^{-}$ collision experiments. These newly defined FFs can be further applied in semi-inclusive deep inelastic scattering processes for the study of nucleon structures.

The hadronic form factors of $B_c$ semileptonic decays to the $P$–wave charmonium 4-plet can be expressed near the zero-recoil point in terms of universal functions, performing a systematic expansion in QCD in the relative velocity of the heavy quarks and in $1/m_Q$. Such functions are independent of the member of the multiplet involved in the transitions. We present the results of a next-to-leading order calculation up to $O(1/m_Q^2)$ classifying the universal functions at this order. We work out a set of relations among the form factors of the same mode and of different modes, which should be reproduced by explicit calculations, reducing the hadronic uncertainty affecting such channels. The approach is also helpful to investigate the debated nature of ${\chi }_{c1}(3872)$, studying the production in $B_c$ semileptonic decays and comparing it to the modes involving the other $2P$ charmonia.

The LHCb collaboration has found that the production rate of $X(3872)$ in proton-proton collisions decreases as final state particle multiplicity increases. Moreover, the ALICE experiment at CERN has observed that the number of deuterons produced increases with multiplicity, a behavior that is qualitatively different from that of the $X(3872)$. These experimental findings may point to a compact structure for the $X(3872)$ or, at least, that its hadronization could proceed through a charm-anticharm core. We have recently used a diffusion Monte Carlo method to solve the 4-body Schrödinger equation that describes the $X(3872)$ as a $c\overline{c}q\overline{q}$ tetraquark system with quantum numbers $I^G(J^{PC})=0^{+}(1^{++})$ and $1^{-}(1^{++})$. According to our structural analysis, the quark–(anti)quark correlations resemble light-meson–heavy-meson molecules of type $\omega J/\psi$ and $\rho J/\psi$, rather than the most extended $D{\overline{D}}^{*}$ interpretation. It was argued that this fact may be the key to make compatible the molecular features of the $X(3872)$ with its production observables. The same formalism allows us to compute the first color excited $c\overline{c}q\overline{q}$ tetraquark state with either $I^G(J^{PC})=0^{+}(1^{++})$ or $1^{-}(1^{++})$. A bound-state is found in each channel, their masses are around 4.0 GeV which is an energy region where many new exotic candidates have been collected by the Particle Data Group. Concerning their structural properties, these states cluster in a compact diquark-antidiquark arrangement which matches perfectly with a so-called Born-Oppenheimer tetraquark configuration. The promptly production rates of these states in proton-proton, proton-nucleus and nucleus-nucleus collisions should fall off equal to or even faster than those of the $X(3872)$.

We compute the leading-twist T-odd quasidistributions of the proton in a spectator model with scalar and axial-vector diquarks: the quasi-Sivers function ${\tilde{f}}_{1T}^{\perp }(x,{\mathit{k}}_T^2;P_z)$ and the quasi-Boer-Mulders function ${\tilde{h}}_1^{\perp }(x,{\mathit{k}}_T^2;P_z)$. We obtain the quark-quark correlators in the four-dimensional Euclidian space by replacing ${\gamma }^{+}$ and ${\sigma }^{i+}$ in the light-cone frame with ${\gamma }_z$ and ${\sigma }_{iz}$. We show by analytical calculation that the results of ${\tilde{f}}_{1T}^{\perp }$ and ${\tilde{h}}_1^{\perp }$ derived from the correlators can reduce to the expressions of the corresponding standard T-odd distributions $f_{1T}^{\perp }(x,{\mathit{k}}_T^2)$ and $h_1^{\perp }(x,{\mathit{k}}_T^2)$ in the limit $P_z\to \infty$. The numerical results for these quasidistributions and their first transverse moments for the $u$ and $d$ quarks in different $x$ and $P_z$ regions are also presented. We find that ${\tilde{f}}_{1T}^{\perp (1)}(x,P_z)$ and ${\tilde{h}}_1^{\perp (1)}(x,P_z)$ in the spectator model are fair approximations to the standard ones (within 20%–30%) in the region $0.1<x<0.5$ when $P_z\ge 2.5–3\mathrm{GeV}$. This supports the idea of using T-odd quasidistributions to obtain standard distributions in the region $P_z>2.5\mathrm{GeV}$ as fair approximation.

Recently, the LHCb Collaboration reported a near-threshold enhancement $X(3960)$ in the $D_s^{+}{D}_s^{-}$ invariant mass distribution. We show that the data can be well described by either a bound or a virtual state below the $D_s^{+}{D}_s^{-}$ threshold. The mass given by the pole position is ($3928\pm 3$) MeV. Using this mass and the existing information on the $X(3872)$ and $Z_c(3900)$ resonances, a complete spectrum of the $S$-wave hadronic molecules formed by a pair of ground state charmed and anticharmed mesons is established. Thus, pole positions of the partners of the $X(3872)$, $Z_c(3900)$, and the newly observed $D_s^{+}{D}_s^{-}$ state are predicted. Calculations have been carried out at the leading order of nonrelativistic effective field theory and considering both heavy quark spin and light flavor SU(3) symmetries, though conservative errors from the breaking of these symmetries are provided.

Experiments aiming to directly detect dark matter through particle recoils can achieve energy thresholds of $\mathcal{O}(10\mathrm{eV})$. In this regime, ionization signals from small-angle Compton scatters of environmental $\gamma$ rays constitute a significant background. Monte Carlo simulations used to build background models have not been experimentally validated at these low energies. We report a precision measurement of Compton scattering on silicon atomic shell electrons down to 23 eV. A skipper charge-coupled device with single-electron resolution, developed for the DAMIC-M experiment, was exposed to a ${}^{241}\text{Am}$ $\gamma$-ray source over several months. Features associated with the silicon K-, ${\mathrm{L}}_1$-, and ${\mathrm{L}}_{2,3}$-shells are clearly identified, and scattering on valence electrons is detected for the first time below 100 eV. We find that the relativistic impulse approximation for Compton scattering, which is implemented in Monte Carlo simulations commonly used by direct detection experiments, does not reproduce the measured spectrum below 0.5 keV. The data are in better agreement with ab initio calculations originally developed for x-ray absorption spectroscopy.

The Collins-Soper kernel is a powerful tool for studying the properties of the QCD vacuum and an essential component of the transverse momentum dependent (TMD) factorization theorem. In this paper, we present a novel method for determining the Collins-Soper kernel directly from the comparison of differential cross sections measured at different energies. The method relies solely on the structure of the TMD factorization theorem and thus also provides a direct test of the theorem validity. With minor modifications, the procedure can be applied to the real measured data for Drell-Yan and SIDIS processes. As a demonstration, we analyze the pseudodata generated by the CASCADE event generator and determine the Collins-Soper kernel suggested by the parton branching model.

We study the generation and propagation of gravitational waves in scalar-tensor gravity using numerical relativity simulations of scalar field collapses beyond spherical symmetry. This allows us to compare the tensor and additional massive scalar waves that are excited. As shown in previous work in spherical symmetry, massive propagating scalar waves decay faster than $1/r$ and disperse, resulting in an inverse chirp. These effects obscure the ringdown in any extracted signal by mixing it with the transient responses of the collapse during propagation. In this paper we present a simple method to rewind the extracted signals to horizon formation, which allows us to clearly identify the ringdown phase and extract the amplitudes of the scalar quasinormal modes, quantifying their excitation in strong gravity events and verifying the frequencies to perturbative calculations. The effects studied are relevant to any theories in which the propagating waves have a dispersion relation, including the tensor case.

Extreme-mass-ratio inspirals (EMRIs) are one of the most exciting and promising target sources for space-based interferometers (such as LISA, Taiji, and TianQin). The observation of their emitted gravitational waves will offer stringent tests on general theory of relativity and provide a wealth of information about the dense environment in galactic centers. To unlock such potential, it is necessary to correctly characterize EMRI signals. However, resonances are a phenomena that occurs in EMRI systems and can impact parameter inference, and therefore the science outcome, if not properly modeled. Here, we explore how to model resonances and develop an efficient implementation. Our previous work has demonstrated that tidal resonances induced by the tidal field of a nearby astrophysical object alters the orbital evolution, leading to a significant dephasing across observable parameter space. Here, we extensively explore a more generic model for the tidal perturber with additional resonance combinations, to study the dependence of resonance strength on the intrinsic orbital and tidal parameters. To analyze the resonant signals, accurate templates that correctly incorporate the effects of the tidal field are required. The evolution through resonances is obtained using a step function, whose amplitude is calculated using an analytic interpolation of the resonance jumps. We benchmark this procedure by comparing our approximate method to a numerical evolution. We find that there is no significant error caused by this simplified prescription, as far as the astronomically reasonable range in the parameter space is concerned. Further, we use Fisher matrices to study both the measurement precision of parameters and the systematic bias due to inaccurate modeling. Modeling of self-force resonances can also be carried out using the implementation presented in this study, which will be crucial for EMRI waveform modeling.

We present a new machine learning-based Monte Carlo event generator using generative adversarial networks (GANs) that can be trained with calibrated detector simulations to construct a vertex-level event generator free of theoretical assumptions about femtometer scale physics. Our framework includes a GAN-based detector folding as a fast-surrogate model that mimics detector simulators. The framework is tested and validated on simulated inclusive deep-inelastic scattering data along with existing parametrizations for detector simulation, with uncertainty quantification based on a statistical bootstrapping technique. Our results provide for the first time a realistic proof of concept to mitigate theory bias in inferring vertex-level event distributions needed to reconstruct physical observables.

We discuss vacuum structure and vacuum stability in classically scale-invariant renormalizable models with a scalar dark matter multiplet of global $\mathcal{O}(N)$ symmetry together with an electroweak singlet scalar mediator. Our conformally invariant scalar potential generates the electroweak symmetry breaking via the Coleman-Weinberg mechanism, and the new scalar singlet mediator acquires its mass through radiative corrections of the scalar dark matters as well as of the standard model particles. Taking into account the present collider bounds, we find the region of parameter space where the scalar potential is stable and all the massless couplings are perturbative up to the Planck scale. With the obtained parameter sets satisfying the vacuum stability condition, we present the allowed region of new physics parameters satisfying the recent measurement of relic abundance and predict the elastic scattering cross section of the new scalar multiplet into target nuclei for a direct detection of the dark matter. We also discuss the collider signatures and future discovery potentials of the new scalars.

We enumerate various effective couplings that contribute to the mixings between an exotic vector boson $Z^{\prime }$ and the neutral electroweak vector bosons. The miscellaneous mixing patterns can be evaluated perturbatively. The effective oblique parameters $S^{\prime }$, $T^{\prime }$, and $U^{\prime }$ are calculated to compare with the electroweak precision test results. With the contributions to the non-negligible $U^{\prime }$ parameter from the ${\epsilon }_{B,W}$ parameters and the aid of some other parameters to cancel the negative $T^{\prime }$, the recent CDF $W$-mass anomaly can therefore be explained.

We present updated results for the form factors of the kaon semileptonic $(K_{\ell 3})$ decay process calculated with $N_f=2+1$ nonperturbatively $O(a)$-improved Wilson quark action and Iwasaki gauge action at the physical point on large volumes of more than $(10\mathrm{fm}{)}^4$. In addition to our previous calculation at the lattice spacing $a=0.085\mathrm{fm}$, we perform a calculation at the second lattice spacing of 0.063 fm. Using the results for the form factors extracted from 3-point functions with the local and also conserved vector currents at the two lattice spacings, continuum extrapolation and interpolation of the momentum transfer are carried out simultaneously to obtain the value of the form factor $f_{+}(0)$ at the zero momentum transfer in the continuum limit. After investigation of stability of $f_{+}(0)$ against several fit forms and different data, we obtain $f_{+}(0)=0.9615(10)({}_{-3}^{+47})(5)$, where the first, second, and third errors are statistical, systematic errors from choice of the fit forms and isospin breaking effect, respectively. Furthermore, we obtain the slope and curvature of the form factors, and the phase space integral from the momentum transfer dependence of the form factors. Combining our value of $f_{+}(0)$ and experimental input of the $K_{\ell 3}$ decay, one of the Cabibbo-Kobayashi-Maskawa matrix elements $|V_{us}|$ is determined as $|V_{us}|=0.2252({}_{-12}^{+5})$, whose error contains the experimental one as well as that in the lattice calculation. This value is reasonably consistent with the ones determined from recent lattice QCD results of $f_{+}(0)$ and also the one determined through the kaon leptonic decay process. We observe some tension between our value and $|V_{us}|$ evaluated from the unitarity of the CKM matrix with $|V_{ud}|$, while it depends on the size of the error of $|V_{ud}|$. It is also found that $|V_{us}|$ determined with our phase space integrals through six $K_{\ell 3}$ decay processes is consistent with the above one using $f_{+}(0)$.