In general, the constituents of the bulk matter produced in heavy-ion collisions carry, besides electric charge, multiple other conserved quantum numbers like baryon number and strangeness. Therefore, an electric field will not only generate an electric current but, at the same time, also currents in baryon number and strangeness. We propose that the impact of the electric field on these conserved currents should be characterized by additional transport coefficients, which we call cross-conductivities. In this paper, we introduce and present a calculation of these cross-conductivities from the Green-Kubo formalism within the transport code SMASH for different chemical compositions of hadron resonance gases. We find that the coefficients underlie an ordering in the active degrees of freedom and that thus the chemical composition of the system plays a crucial role. Further, we argue that in future comparisons of lattice QCD calculations with these findings, one could constrain which degrees of freedom and their corresponding charge properties are relevant for the QCD dynamics of the system.

We study the exclusive electroproduction of a photon pair in the kinematical regime where the diphoton invariant mass is large and where the nucleon flies almost in its original direction. We discuss the relative importance of the QCD process where the two photons originate from a quark line compared to the single (double) Bethe-Heitler processes where one (two) photons originate from the lepton line. This process turns out to be a promising tool to study generalized parton distributions in the nucleon, both at the medium energy of JLab and at a high energy electron ion collider.

The quark parts of the gravitational form factors of hyperons are calculated by means of the light-cone QCD sum rule. In the calculations, the distribution amplitudes (DAs) of $\mathrm{\Sigma }$, $\mathrm{\Xi }$, and $\mathrm{\Lambda }$ together with the general forms of their interpolating currents as well as the quark part of the energy-momentum tensor current are used. These form factors can provide information on their mass and distributions of the angular momentum, energy and pressure inside the hyperons. It is obtained that the $Q^2$ dependencies of the hyperon gravitational form factors are nicely characterized by a multipole fit function. Using the fits of these form factors, some mechanical properties such as the mechanical radius of the hyperons and the pressure and energy distributions at the center of these particles are obtained. The obtained results can help us in better understanding of the internal structures of these baryons and the QCD as theory of the strong interaction.

Black holes have turned into cosmic laboratories to search for ultralight scalars by virtue of the superradiant instability. In this paper we present a detailed study of the impact of the superradiant evolution on the black hole shadow and investigate the exciting possibility to explore it with future observations of very long baseline interferometry. We simulated the superradiant evolution numerically, in the adiabatic regime, and derived analytic approximations modeling the process. Driven by superradiance, we evolve the black hole shadow diameter and (i) find that it can change by a few $\mu \mathrm{as}$, just below the current resolution of the Event Horizon Telescope, albeit on timescales that are longer than realistic observation times; (ii) show that the shadow diameter can either shrink or grow; and (iii) explore in detail how the shadow’s end state is determined by the initial parameters and coupling.

We consider static and cylindrically symmetric interior string-type solutions in the scalar-tensor representation of the hybrid metric-Palatini modified theory of gravity. As a first step in our study, we obtain the gravitational field equations and further simplify the analysis by imposing Lorentz invariance along the $t$ and $z$ axes, which reduces the number of unknown metric tensor components to a single function $W^2(r)$. In this case, the general solution of the field equations can be obtained, for an arbitrary form of the scalar field potential, in an exact closed parametric form, with the scalar field $\varphi$ taken as a parameter. We consider in detail several exact solutions of the field equations, corresponding to a null and constant potential, and to a power-law potential of the form $V(\varphi )=V_0{\varphi }^{3/4}$, in which the behaviors of the scalar field, of the metric tensor components, and of the string tension can be described in a simple mathematical form. We also investigate the string models with exponential and Higgs-type scalar field potentials by using numerical methods. In this way, we obtain a large class of novel stable stringlike solutions in the context of hybrid metric-Palatini gravity, in which the basic parameters, such as the scalar field, metric tensor components, and string tension, depend essentially on the initial values of the scalar field, and of its derivative, on the $r=0$ circular axis.

A cosmic pseudo-Nambu-Goldstone boson has been proposed to resolve the four-sigma discrepancy between precision measurements of the expansion rate of the universe. We show this solution may also produce a cosmic birefringence (CB) signal in the polarization of the cosmic microwave background (CMB); observations of the CB power spectrum and cross-correlation with the CMB can independently confirm the presence of this new boson. We find significant new contributions to the CB signal, and show that future CMB experiments will greatly improve sensitivity to CB and Hubble tension scenarios.

There have been vigorous research attempts to test various modified gravity theories by using the physics of the cosmic microwave background (CMB). Meanwhile, symmetry breaking such as the Higgs mechanism is one of the most important phenomena in physics, but there has not been much research to investigate them by cosmological observations. In this article, with the CMB power spectra, we try to distinguish two different scenarios of spontaneous symmetry breaking in the primordial era of the Universe. The first model is based on a broken-symmetric theory of gravity, which was suggested by Zee in 1979. The second model is an application of Palatini formalism to the first model. Perturbation equations are computed and they show that the differences originated from the property of symmetry. Furthermore, it turns out that the two models have different features of the CMB power spectra with the same potential scale. This fact enables us to verify distinct kinds of primordial symmetry breaking with CMB physics.

Ambient neutrons may cause significant background for underground experiments. Therefore, it is necessary to investigate their flux and energy spectrum in order to devise a proper shielding. Here, two sets of altogether ten moderated ${}^3\mathrm{He}$ neutron counters are used for a detailed study of the ambient neutron background in tunnel IV of the Felsenkeller facility, underground below 45 m of rock in Dresden/Germany. One of the moderators is lined with lead and thus sensitive to neutrons of energies higher than 10 MeV. For each ${}^3\mathrm{He}$ counter moderator assembly, the energy-dependent neutron sensitivity was calculated with the FLUKA code. The count rates of the ten detectors were then fitted with the MAXED and GRAVEL packages. As a result, both the neutron energy spectrum from ${10}^{-9}$ to 300 MeV and the flux integrated over the same energy range were determined experimentally. The data show that at a given depth, both the flux and the spectrum vary significantly depending on local conditions. Energy-integrated fluxes of ($0.61\pm 0.05$), ($1.96\pm 0.15$), and $(4.6\pm 0.4)\times {10}^{-4}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, respectively, are measured for three sites within Felsenkeller tunnel IV which have similar muon flux but different shielding wall configurations. The integrated neutron flux data and the obtained spectra for the three sites are matched reasonably well by FLUKA Monte Carlo calculations that are based on the known muon flux and composition of the measurement room walls.

Warm dark matter has recently become increasingly constrained by observational inferences about the low-mass end of the subhalo mass function, which would be suppressed by dark matter free streaming in the early Universe. In this work, we point out that a constraint can be placed on ultralight bosonic dark matter (often referred to as “fuzzy dark matter”) based on similar considerations. Recent limits on warm dark matter from strong gravitational lensing of quasars and from fluctuations in stellar streams separately translate to a lower limit of $\sim 2.1\times {10}^{-21}\mathrm{eV}$ on the mass of an ultralight boson comprising all dark matter. These limits are complementary to constraints on ultralight dark matter from the Lyman-$\alpha$ forest and are subject to a completely different set of assumptions and systematic uncertainties. Taken together, these probes strongly suggest that dark matter with a mass $\sim {10}^{-22}\mathrm{eV}$ is not a viable way to reconcile differences between cold dark matter simulations and observations of structure on small scales.

This work is devoted to the discussion and characterization of the tensor $2^{-(-)}$ meson spectrum, by making use of the Coulomb gauge Hamiltonian approach to QCD, with the interactions being given by an improved confining potential and a transverse hyperfine interaction, whose kernel is a Yukawa-type potential. Our aim is to study the basic features of $2^{-(-)}$ mesons within an unified framework through the whole range of quark masses. We concentrate our investigation on predictions of expected but yet-unobserved ground states of unflavored light mesons and on charmonium and bottomonium states. The numerical results are compared with existing literature.

We investigate a dark matter model involving an inert $\mathrm{SU}(2{)}_{\mathrm{L}}$ quadruplet scalar with hypercharge $1/2$. After the electroweak symmetry breaking, the dark sector contains one doubly charged, two singly charged, and two neutral scalars. The lighter neutral scalar can be a viable dark matter candidate. Electroweak production of these scalars at the Large Hadron Collider leads to potential signals in the $\text{monojet}+{\cancel{E}}_{\mathrm{T}}$ and $\mathrm{soft}-\mathrm{leptons}+\text{jets}+{\cancel{E}}_{\mathrm{T}}$ channels. We thus derive constraints on the model by reinterpreting recent experimental searches. Based on simulation, we further evaluate the sensitivity at a future 100 TeV $pp$ collider.

Deciphering the complex information contained in jets produced in collider events requires a physical organization of the jet data. We introduce two-particle correlations (2PCs) by pairing individual particles as the initial jet representation from which a probabilistic model can be built. Particle momenta as well as particle types and vertex information are included in the correlation. A novel, two-particle correlation neural network (2PCNN) architecture is constructed by combining neural-network-based filters on 2PCs and a deep neural network for capturing jet kinematic information. The 2PCNN is applied to boosted boson and heavy flavor tagging, and it achieves excellent performance by comparing to image-based convolutional neural network and telescoping deconstruction. Major correlation pairs exploited in the trained models are also identified, which shed light on the physical significance of certain jet substructure.

The processes $e^{+}{e}^{-}\to D_s^{+}{D}_{s1}(2460{)}^{-}+\mathrm{c}.\mathrm{c}.$ and $e^{+}{e}^{-}\to D_s^{*+}{D}_{s1}(2460{)}^{-}+\mathrm{c}.\mathrm{c}.$ are studied for the first time using data samples collected with the BESIII detector at the BEPCII collider. The Born cross sections of $e^{+}{e}^{-}\to D_s^{+}{D}_{s1}(2460{)}^{-}+\mathrm{c}.\mathrm{c}.$ at nine center-of-mass energies between 4.467 GeV and 4.600 GeV and those of $e^{+}{e}^{-}\to D_s^{*+}{D}_{s1}(2460{)}^{-}+\mathrm{c}.\mathrm{c}.$ at $\sqrt{s}=4.590\mathrm{GeV}$ and 4.600 GeV are measured. No obvious charmonium or charmoniumlike structure is seen in the measured cross sections.

A detailed canonical treatment of a new action for a nonrelativistic particle coupled to background gravity, recently given by R. Banerjee and P. Mukherjee [Phys. Lett. B 797, 134484 (2019); 797, 134834 (2019)], is performed both in the Lagrangian and Hamiltonian formulations. The equation of motion is shown to satisfy the geodesic equation in the Newton-Cartan background, thereby clearing certain confusions. The Hamiltonian analysis is done in the gauge-independent as well as gauge fixed approaches, following Dirac’s analysis of constraints. The physical (canonical) variables are identified, and the path to canonical quantization is outlined by explicitly deriving the Schrödinger equation. Usual flat space results are correctly reproduced.

We consider perturbations of closed Friedmann universes. Perturbation modes of two lowest wave numbers ($L=0$ and 1) are generally known to be fictitious, but here we show that both are physical. The issue is more subtle in Einstein static universes where closed background space has a timelike Killing vector with the consequent occurrence of linearization instability. Proper solutions of the linearized equation need to satisfy the Taub constraint on a quadratic combination of first-order variables. We evaluate the Taub constraint in the two available fundamental gauge conditions, and show that in both gauges the $L\ge 1$ modes should accompany the $L=0$ (homogeneous) mode for vanishing sound speed, $c_s$. For $c_s^2>1/5$ (a scalar field supported Einstein static model belongs to this case with $c_s^2=1$), the $L\ge 2$ modes are known to be stable. In order to have a stable Einstein static evolutionary stage in the early universe, before inflation and without singularity, although the Taub constraint does not forbid it, we need to find a mechanism to suppress the unstable $L=0$ and $L=1$ modes.

A small fraction, $f$, of cosmic string loops can collapse to form primordial black holes (PBHs). Constraints on the abundance of PBHs can therefore be used to constrain $f$. We update these calculations, taking into account the PBH extended mass function, and find $f<{10}^{-31}(G\mu /c^2{)}^{-3/2}$. This is roughly 1 order of magnitude tighter than previous constraints. The improvement from the tighter constraints on the abundance of PBHs is partly offset by refinements to the theoretical calculation of the cosmic string loop formation rate.

Machine learning (ML) algorithms have revolutionized the way we interpret data in astronomy, particle physics, biology, and even economics, since they can remove biases due to a priori chosen models. Here we apply a particular ML method, the genetic algorithms (GA), to cosmological data that describes the background expansion of the Universe, namely the pantheon Type Ia supernovae and the Hubble expansion history $H(z)$ datasets. We obtain model independent and nonparametric reconstructions of the luminosity distance $d_L(z)$ and Hubble parameter $H(z)$ without assuming any dark energy model or a flat Universe. We then estimate the deceleration parameter $q(z)$, a measure of the acceleration of the Universe, and we make a $\sim 4.5\sigma$ model independent detection of the accelerated expansion, but we also place constraints on the transition redshift of the acceleration phase $(z_{\mathrm{tr}}=0.662\pm 0.027)$. We also find a deviation from $\mathrm{\Lambda }\mathrm{CDM}$ at high redshifts, albeit within the errors, hinting toward the recently alleged tension between the SnIa/quasar data and the cosmological constant $\mathrm{\Lambda }\mathrm{CDM}$ model at high redshifts ($z\gtrsim 1.5$). Finally, we show the GA can be used in complementary null tests of the $\mathrm{\Lambda }\mathrm{CDM}$ via reconstructions of the Hubble parameter and the luminosity distance.

The annihilation of heavy particles close to thermal equilibrium, which plays a prominent role in the chemical equilibration of heavy quarks in the quark-gluon plasma (QGP) as well as in many classic dark matter scenarios, is reexamined. We derive a scattering amplitude that resums near-threshold attractive interaction of the annihilating particles in terms of the nonrelativistic scattering $T$-matrix and Green’s function, thereby capturing the pertinent Sommerfeld enhancement from both nonperturbative scattering state and bound state solutions. The derived formula is of such generality that it applies to arbitrary partial wave processes of two-particle annihilation, and enables us to incorporate finite widths of the annihilating particles. In a screened potential model, the nonperturbative scattering amplitude is computed and the Sommerfeld enhancement is identified for heavy quark-antiquark annihilation in the QGP.

The “gauged” Peccei-Quinn (PQ) mechanism of Fukuda et al. [Phys. Lett. B 771, 327 (2017)] is implemented in the flavorful axion model of Carone and Merchand. This model of flavor is similar to other successful ones based on the double tetrahedral group, but the flavor symmetry includes a global U(1) factor that leads to the presence of a flavorful axion. Here, we gauge that U(1) symmetry and introduce a heavy sector that includes (1) the fermions necessary to cancel anomalies and (2) a second scalar flavon field that spontaneously breaks the U(1) symmetry. The full theory has an accidental $\mathrm{U}(1)\times \mathrm{U}(1{)}^{\prime }$ global symmetry, anomalous with respect to QCD; ${\mathrm{U}(1)}_{\mathrm{PQ}}$ emerges as a linear combination. The gauged flavor symmetry restricts the possible PQ symmetry-breaking higher-dimension operators so that sufficient axion quality is preserved. We provide a model of the quark sector, as a proof of principle, and then a model which incorporates the standard model charged leptons as well. In both cases, the charge assignments that lead to acceptable axion quality also lead to a multiplicity of some of the heavy sector states; we check that the Landau pole for hypercharge remains above the cutoff of the effective theory. We consider relevant phenomenological constraints on these models including those on the predicted axion couplings.

Secret neutrino interactions can play an essential role in the origin of dark matter. We present an anatomy of production mechanisms for sterile neutrino dark matter, a keV-scale gauge-singlet fermion that mixes with active neutrinos, in the presence of a new vector boson mediating secret interactions among active neutrinos. We identify three regimes of the vector boson’s mass and coupling where it makes a distinct impact on dark matter production through the dispersion relations and/or scattering rates. We also analyze models with gauged $L_{\mu }-L_{\tau }$ and $B-L$ numbers which have a similar dark matter cosmology but different vector boson phenomenology. We derive the parameter space in these models where the observed relic abundance is produced for sterile neutrino dark matter. They serve as a well-motivated target for the upcoming experimental searches.