In this work we investigate possible actions for antisymmetric two-tensor field models subject to constraints that force the field to acquire a nonzero vacuum expectation value, thereby spontaneously breaking Lorentz invariance. In order to assure stability, we require that the associate Hamiltonian be bounded from below. It is shown that this requirement rules out any quadratic action constructed only from the antisymmetric tensor field. We then explicitly construct a hybrid model consisting of the antisymmetric two-tensor field together with a vector field, subject to constraints forcing nonzero expectation values, that is stable in Minkowski space.

We study various aspects of modeling astrophysical black holes using the recently introduced semiclassical formalism of physical black holes (PBHs). This approach is based on minimal requirements of observability and regularity of the horizons. We demonstrate that PBHs do not directly couple to the cosmological background in the current epoch, and that their equation of state renders them unsuitable for describing dark energy. Utilizing their properties for the analysis of more exotic models, we present a consistent semiclassical scenario for a black-to-white hole bounce and identify obstacles to the transformation of a black hole horizon to a wormhole throat.

Matching gravitational-wave observations of binary neutron stars with theoretical model predictions reveals important information about the sources, such as the masses and the distance to the stars. The latter can be used to determine the Hubble constant, the rate at which the Universe expands. One general problem of all astrophysical measurements is that theoretical models only approximate the real underlying physics, which can lead to systematic uncertainties introducing biases. However, the extent of this bias for the distance measurement due to uncertainties of gravitational waveform models is unknown. In this study, we analyze a synthetic population of 38 binary neutron star sources measured with Advanced LIGO and Advanced Virgo at design sensitivity. We employ a set of four different waveform models and estimate model-dependent systematic biases on the extraction of the Hubble constant using the bright siren method. Our results indicate that systematic biases are below statistical uncertainties for the current generation of gravitational-wave detectors.

We calculate the one-loop corrections in bispectrum of cosmic microwave background scale perturbations induced from the small-scale modes undergoing an intermediate phase of ultraslow-roll (USR) inflation in scenarios employed for primordial black hole formation. Using the formalism of effective field theory of inflation we calculate the cubic and quartic Hamiltonians and perform the in-in analysis for a subset of Feynman diagrams comprising both the cubic and the quartic exchange vertices. We show the one-loop corrections in bispectrum has the local shape with $f_{\mathrm{NL}}$ having the same structure as the one-loop correction in power spectrum in their dependence on the duration of the USR phase and the sharpness of the transition to the final attractor phase. It is shown that in the models with a sharp transition the induced loop corrections in bispectrum can quickly violate the observational bounds on $f_{\mathrm{NL}}$.

Interactions of cosmic-ray protons and nuclei in their sources and in the interstellar medium produce “hadronic” $\gamma$-ray emission. Gamma rays can also be of “leptonic” origin, i.e., originating from high-energy electrons accelerated together with protons. It is difficult to distinguish between hadronic and leptonic emission mechanisms based on $\gamma$-ray data alone. This can be done via detection of neutrinos, because only hadronic processes lead to neutrino production. We use the publicly available 10 yr IceCube neutrino telescope dataset to demonstrate the hadronic nature of high-energy emission from the direction of the Cygnus region of the Milky Way. We find a $3\sigma$ excess of neutrino events from an extended Cygnus Cocoon, with the flux comparable to the flux of $\gamma$ rays in the multi-TeV energy range seen by HAWC and LHAASO telescopes.

Gravitational-wave observations have just started probing the properties of black hole binary merger populations. The observation of binaries with very massive black holes and significantly asymmetric masses motivates the study of dense star clusters as astrophysical environments which can produce such events dynamically. In this paper we present rapster (for “rapid cluster evolution”), a new code designed to rapidly model binary black hole population synthesis and the evolution of massive star clusters based on simple, yet realistic prescriptions. We also perform a thorough comparison with the Cluster Monte Carlo code and find generally good agreement. The code can be used to generate large populations of dynamically formed binary black holes.

We study the chiral-odd generalized parton distributions (GPDs) of the $\overline{u}$ and $\overline{d}$ quarks inside the proton at zero skewness using the overlap representation within the light-cone formalism. Utilizing the light-cone wave functions of the proton obtained from the baryon-meson fluctuation model in terms of the $|q\overline{q}B⟩$ Fock states, we provide expressions for the GPDs ${\tilde{H}}_T^{\overline{q}/P}(x,0,t)$, $H_T^{\overline{q}/P}(x,0,t)$, and $E_T^{\overline{q}/P}(x,0,t)$ where $\overline{q}=\overline{u}$ and $\overline{d}$. Numerical results for these GPDs in momentum space as well as in impact parameter space are presented. Additionally, we investigate specific combinations of the chiral-odd GPDs in impact parameter space, focusing on the spin-orbit correlation effect of the sea quarks.

We investigate the spin-orbital angular momentum correlations for the active quark inside the light and heavy mesons for both the spin-0 and spin-1 cases. These correlations can be derived from the generalized transverse-momentum-dependent distributions as well as the generalized parton distributions. We employ the overlap representation of light-front wave functions in the light-front quark model to calculate our analytical results. The dependence of spin-orbit correlations (SOCs) on the longitudinal momentum fraction $x$ as well as the transverse-momentum-dependence ${\mathbf{k}}_{\perp }$ is graphically presented. Even though the SOCs have already been studied for the spin-0 pions and kaons in other approaches, no calculations for the other light and heavy spin-0 mesons have been reported in the literature. Further, the correlations for any of the light and heavy spin-1 mesons are studied for the first time in the present work.

We study the jet quenching parameter $\widehat{q}$ in a nonequilibrium plasma using the QCD effective kinetic theory. We discuss subleading terms at large jet momentum $p$, show that our expression for $\widehat{q}$ reproduces thermal results at small and large transverse momentum cutoffs for infinite $p$, and construct an interpolation between these limits to be used in phenomenological applications. Using simple nonequilibrium distributions that model pertinent features of the bottom-up thermalization scenario, we analytically assess how anisotropy, underoccupation, or overoccupation affect the jet quenching parameter. Our work provides more details on the $\widehat{q}$ formula used in our preceding work [Phys. Lett. B 850, 138525 (2024) ] and sets the stage for further numerical studies of jet momentum broadening in the initial stages of heavy-ion collisions from QCD kinetic theory.

In this study, the impact of triangle singularity is investigated in the isospin breaking process $J/\psi \to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\pi$. The triangle singularity is found to play a significant role in the process, resulting in the creation of a resonancelike structure around 1.4 GeV in the $\mathrm{\Lambda }\pi (\overline{\mathrm{\Lambda }}\pi )$ invariant mass spectrum. To amplify the impact of this triangle singularity, the presence of two ${\mathrm{\Sigma }}^{*}({\frac{1}{2}}^{-})$ states around 1.4 GeV and 1.6 GeV is essential, yet these states have not been definitively identified in the current baryon spectrum. We recommend that experiments, particularly the Beijing Spectrometer and the future Super Tau-Charm Factory, investigate the process $J/\psi \to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\pi$ to offer direct evidence for our predicted triangle singularity and additional evidence regarding the $\mathrm{\Sigma }({\frac{1}{2}}^{-})$ states.

We present the basis of dimension-eight operators associated with universal theories. We first derive a complete list of independent dimension-eight operators formed with the Standard Model bosonic fields characteristic of such universal new physics scenarios. Without imposing C or P symmetries the basis contains 175 operators—that is, the assumption of universality reduces the number of independent Standard Model effective field theory (SMEFT) coefficients at dimension eight from 44807 to 175. 89 of the 175 universal operators are included in the general dimension-eight operator basis in the literature. The 86 additional operators involve higher derivatives of the Standard Model bosonic fields and can be rotated in favor of operators involving fermions using the Standard Model equations of motion for the bosonic fields. By doing so we obtain the allowed fermionic operators generated in this class of models which we map into the corresponding 86 independent combinations of operators in the dimension-eight basis of [C. W. Murphy, Dimension-8 operators in the standard model effective field theory, J. High Energy Phys. 10 (2020) 174.].

We simulated spin-spin interactions of $N$-bodies in linearized general relativity (GR) and linearized massive gravity of the Fierz-Pauli type (mGR). It was noted earlier that there is a discrete difference between the spin-spin interaction potential in GR and mGR for a 2-body system, akin to the van Dam-Veltman-Zakharov discontinuity in the static Newton’s potential. Specifically, at large distances, GR favors antiparallel spin orientation with total spin pointing along the interaction axis, while mGR favors parallel spin orientation with total spin perpendicular to the axis between the sources. For an $N$-body system, a simulation in mGR hitherto has not been done and one would like to know the total spin of the system in both theories. Here we remedy this. In the simulations of GR, we observed that the total spin tends to decrease from a random initial configuration, while for mGR with a large distance, the total spin increases.

Nucleon decays are generic predictions of motivated theories, including those based on the unification of forces and supersymmetry. We demonstrate that noncanonical nucleon decays offer a unique opportunity to broadly probe light new particles beyond the Standard Model with masses below $\sim$ few GeV over decades in mass range, including axion-like particles, dark photons, sterile neutrinos, and scalar dark matter. Conventional searches can misinterpret and even completely miss such new physics. We propose a general strategy based on momenta of visible decay final states to probe these processes, offering a rich physics program for existing and upcoming experiments such as Super-Kamiokande, Hyper-Kamiokande, DUNE, and JUNO.

Based on $368.5\mathrm{p}{\mathrm{b}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at center-of-mass energies 4.914 and 4.946 GeV by the BESIII detector, the $e^{+}{e}^{-}\to \varphi {\chi }_{c1}(3872)$ process is searched for the first time. No significant signal is observed and the upper limits at the 90% confidence level on the product of the Born cross section $\sigma (e^{+}{e}^{-}\to \varphi {\chi }_{c1}(3872))$ and the branching fraction $\mathcal{B}[{\chi }_{c1}(3872)\to {\pi }^{+}{\pi }^{-}J/\psi ]$ at 4.914 and 4.946 GeV are set to be 0.85 and 0.96 pb, respectively. These measurements provide useful information for the production of the ${\chi }_{c1}(3872)$ at $e^{+}{e}^{-}$ colliders and deepen our understanding about the nature of this particle.

Within the framework of the Einstein-Maxwell-dilaton model, which incorporates information on the equation of state and baryon number susceptibility from lattice results, we have conducted a comprehensive analysis of the potential energy, running coupling, and dissociation time for heavy-quark–antiquark pairs using gauge/gravity duality. This study encompasses various systems, including pure gluon systems, 2-flavor systems, $2+1$-flavor systems, and $2+1+1$-flavor systems under finite temperature and chemical potential. The results reveal that the linear component of the potential energy diminishes as the flavor increases. It is also found that our results are extremely close to the recent lattice results for $2+1$-flavors at finite temperature. Moreover, we have thoroughly investigated the dissociation distance and effective running coupling constant of quark-antiquark pairs to gain a comprehensive understanding of their behavior across various flavors. Finally, we have examined real-time dynamics of quark dissociation. The findings indicate that the dissociation time of quark-antiquark pairs is dependent on temperature, chemical potential, and flavor of the systems.

Recently, the complexity equals any gravitational observable conjecture has been proposed in [Phys. Rev. Lett. 128, 081602 (2022)], which is an extension of the complexity equals volume proposal. These gravitational observables are referred to as generalized volumes. In this paper, we investigate the generalized volume complexity for black holes with one or two horizons respectively. We verify that the turning time is universal and independent of the Cauchy horizon. Not only does this phase transition occur once, but it may also occur two or more times depending on the number and height of the effective potential peaks. On the other hand, we confirm that the generalized volume complexity can be divided based on the shape of the effective potential. We then discuss the nonsmooth transition from the Reissner–Nordström–anti-de Sitter (AdS) black hole to the Schwarzschild-AdS black hole.

Wave propagation is a common occurrence in all of physics. A linear approximation provides a simpler way to describe various fields related to observable phenomena in laboratory physics as well as astronomy and cosmology, allowing us to probe gravitation through its effect on the trajectories of particles associated with those fields. This paper proposes a unified framework to describe the wave propagation of a set of interacting tensor fields that obey coupled homogeneous linear second-order partial differential equations for arbitrary curved spacetimes, both Lorentzian and metric-affine. We use Jeffreys-Wentzel-Kramers-Brillouin (JWKB) Ansätze for all fields, written in terms of a perturbation parameter proportional to a representative wavelength among them, deriving a set of hierarchical algebraic and differential equations that link the fields’ phases and different order amplitudes. This allows us to reobtain the well-known laws of geometrical optics and beyond geometrical optics in a generalized form, showing that these laws are independent of the rank of the fields involved. This is true as long as what we refer to as the kinetic tensor of a given field satisfies a set of diagonality conditions, which further imply a handful of simplifications on the transport equations obtained in the subleading orders of the JWKB Ansätze. We explore these results in several notable examples in Lorentzian and metric-affine spacetimes, illustrating the reach of our derivations in general relativity, reduced Horndeski theories, spacetimes with completely antisymmetric torsion, and Weyl spacetimes. The formalism presented herein lays the groundwork for the study of rays associated with different types of waves in curved spacetimes and provides the tools to compute modifications to their brightness evolution laws, consequential distance duality relations, and beyond geometrical optics phenomena.

Alternative theories of gravity may be put to the test by making use of gravitational wave observations. Scalar-tensor theories provide a relatively simple framework that allows for compact object solutions with characteristics different from those of their general relativity counterparts. In shift-symmetric theories, black hole hair may arise when a linear coupling with the Gauss-Bonnet invariant is introduced. The effect of this coupling on the black hole quasinormal modes (QNMs) has been shown to be small, therefore limiting the observational interest in the theory. In general, however, one expects that additional shift-symmetric terms in the Lagrangian may be relevant, and indeed, it has been shown that they can have a nontrivial impact on the mass and scalar charge of the stationary solutions. In this work we explore the effect that various such terms have on the axial and polar QNMs of the hairy black hole solutions.

Within the disk-corona model, it is natural to expect that a fraction of reflection photons from the disk are Compton scattered by the hot corona (reflection Comptonization), even if this effect is usually ignored in x-ray reflection spectroscopy studies. We study this effect by using NICER and NuSTAR data of the Galactic black hole EXO 1846-031 in the hard-intermediate state with the model simplcutx. Our analysis suggests that a scattered fraction of order 10% is required to fit the data, but the inclusion of reflection Comptonization does not change appreciably the measurements of key parameters like the black hole spin and the inclination angle of the disk.