The expansion history and thermal physical process that happened in the early Universe before big bang nucleosynthesis (BBN) remains relatively unconstrained by observations. Low reheating temperature universes with normalcy temperatures of $T_{\mathrm{RH}}\sim 2\mathrm{MeV}$ remain consistent with primordial nucleosynthesis and accommodate several new physics scenarios that would normally be constrained by high-temperature reheating models, including massive sterile neutrinos. We explore such scenarios’ production of keV-scale sterile neutrinos and their resulting constraints from cosmological observations. The parameter space for massive sterile neutrinos is much less constrained than in high-$T_{\mathrm{RH}}$ thermal histories, though several cosmological constraints remain. Such parameter space is the target of several current and upcoming laboratory experiments such as TRISTAN (KATRIN), HUNTER, MAGNETO-$\nu$, and PTOLEMY. Cosmological constraints remain stringent for stable keV-scale sterile neutrinos. However, we show that sterile neutrinos with a dark decay to radiation through a $Z^{\prime }$ or a new scalar are largely unconstrained by cosmology. In addition, this mechanism of sterile neutrinos with large mixing may provide a solution to the Hubble tension. We find that keV-scale sterile neutrinos are therefore one of the best probes of the untested pre-BBN era in the early Universe and could be seen in upcoming laboratory experiments.

The Galactic Center excess (GCE), one of the most remarkable discoveries by Fermi-LAT, has prompted extensive exploration over the past decade, often attributed to dark matter or millisecond pulsars. This work proposes a novel interpretation on the origin of the GCE, focusing on the observed spectral shape. Protons are accelerated at the Galactic Center and collide with the neutron cluster on the surface of the nonrotating neutron stars. Due to the gluon condensation in nucleons, these collisions produce a large number of mesons, which have reached to the saturation state and subsequently generate the broken power law in the gamma ray spectra. We explained the spectral shape of GCE using the gluon condensation and an assumption of existing the nonrotating neutron stars at the Galactic Center. This example of the gluon condensation mechanism not only expands the applications of the hadronic scenario in the cosmic gamma ray spectra but also provides a new evidence of the gluon condensation.

In-medium masses of the light vector $\omega$, $\rho$ and axial-vector $A_1$ mesons are studied in the magnetized nuclear matter, accounting for the effects of (inverse) magnetic catalysis at finite temperature. The in-medium partial decay widths for the $A_1\to \rho \pi$ channels are studied from the in-medium masses of the initial and the final state particles by applying a phenomenological Lagrangian to account for the $A_1\rho \pi$ interaction vertices. The masses are calculated within the QCD sum rule framework, with the medium effects coming through the light quark ($\sim ⟨\overline{q}q⟩$) and the scalar gluon condensates ($\sim ⟨G^2⟩$), as well as the light four-quark condensate ($\sim ⟨\overline{q}q{⟩}^2$). The condensates are calculated within the chiral $SU(3)$ model in terms of the medium modified scalar fields: isoscalar $\sigma$, $\zeta$, isovector $\delta$, and the dilaton field $\chi$. The effects of magnetic fields are incorporated through the magnetized Dirac sea contribution as well as the Landau energy levels of protons and anomalous magnetic moments (AMMs) of the nucleons at finite temperature nuclear matter. The effects of temperature are included through the Fermi distribution functions in the number (${\rho }_{p,n}$) and scalar (${\rho }_{p,n}^s$) densities of nucleons within the chiral effective model framework. The incorporation of the magnetic field through the Dirac sea of nucleons lead to an enhancement (reduction) of the light quark condensates with magnetic field, give rise to the phenomenon of magnetic (inverse) catalysis. The effects of (inverse) magnetic catalysis at finite temperature nuclear matter are studied on the spectral functions and production cross sections of the neutral $\rho$ and $A_1$ mesons. This may affect the production of the light vector and axial-vector mesons in the peripheral heavy-ion collision experiments, where estimated magnetic field is very large at the early stages of collisions with very high temperature.

Based on a data sample of $(10087\pm 44)\times {10}^{6}J/\psi$ events collected with the BESIII detector, the branching fraction of $J/\psi \to \overline{\mathrm{\Lambda }}{\pi }^{+}{\mathrm{\Sigma }}^{-}+\mathrm{c}.\mathrm{c}.$ is measured to be $(1.221\pm 0.002\pm 0.038)\times {10}^{-3}$, and the branching fraction of its isospin partner mode $J/\psi \to \overline{\mathrm{\Lambda }}{\pi }^{-}{\mathrm{\Sigma }}^{+}+\mathrm{c}.\mathrm{c}.$ is measured to be $(1.244\pm 0.002\pm 0.045)\times {10}^{-3}$ with improved precision. Here the first uncertainties are statistical and the second ones systematic. The isospin symmetry of the $\mathrm{\Sigma }$ baryon in charmonium hadronic decay and the “12% rule” are tested, and no violation is found. The potential of using these channels as $\mathrm{\Sigma }$ baryon sources for nuclear physics research is studied, and the momentum and angular distributions of these sources are provided.

We present a study of the process $e^{+}{e}^{-}\to \eta \varphi$ using data samples collected with the BESIII detector corresponding to an integrated luminosity of $15.03{\mathrm{fb}}^{-1}$ at 23 center-of-mass energies from 3.773 to 4.600 GeV. The Born cross sections are measured at each energy, and a coherent fit to cross section line shape is performed using a Breit-Wigner parametrization to search for charmoniumlike vector states. No significant signals of the $Y(4230)$ and $Y(4360)$ resonances are observed.

We examine the temporal evolution of the modular entropy and capacity (in particular, the fluctuation of the entanglement entropy) for systems of time-dependent oscillators coupled by a (time-dependent) parameter. Such models, through the discretization procedure, fit into field theory problems arising from quench phenomena or nonstatic spacetimes. First, we compare the dynamics of the modular and Rényi entropies and derive the form of the modular capacity for the single time-dependent oscillator as well as chains with bipartite decompositions. In the latter case we analyze distinguished periodicities during the evolution and the role of various boundary conditions. Next, we focus on the dynamics of the capacity (fluctuation) of entanglement. We compare the results obtained with the predictions of quasiparticles models; in particular, we obtain a theoretical value of the initial slope of the capacity for abrupt quenches. We study also continuous protocols with the frequency that vanishes at plus (and minus) infinity, including a model in which the frequency tends to the Dirac delta. All the above issues are discussed with the emphasis on the analytical methods.

In this paper, we delve into the significance of local scale symmetry and the role of the associated noether current, within gravitational theories which are based in non-riemannian background space. Our focus is in Weyl and in Riemann-Cartan geometry based gravitational theories. We show that local scale symmetry is associated with the vanishing noether current whenever there are not new propagating gravitational degrees of freedom beyond the two polarizations of the massless graviton. In contrast, in local scale invariant theories where there are more than two propagating gravitational degrees of freedom, local scale symmetry is associated with nonvanishing noether current. The known result that Weyl symmetry has a vanishing noether current is generalized to non-riemannian gravitational theories. An exception are the local scale invariant gravitational theories with vectorial nonmetricity, where the associated noether current is nonvanishing.

We provide accurate universal relations that allow to estimate the moment of inertia $I$ and the ratio of kinetic to gravitational binding energy $T/W$ of uniformly rotating neutron stars from the knowledge of mass, radius, and moment of inertia of an associated nonrotating neutron star. Based on these, several other fluid quantities can be estimated as well. Astrophysical neutron stars rotate to varying degrees, and, although rotational effects may be neglected in some cases, not modeling them will inevitably introduce bias when performing parameter estimation. This is especially important for future, high-precision measurements coming from electromagnetic and gravitational wave observations. The proposed universal relations facilitate computationally cheap equation of state inference codes that permit the inclusion of observations of rotating neutron stars. To demonstrate this, we deploy them into a recent Bayesian framework for equation of state parameter estimation that is now valid for arbitrary, uniform rotation. Our inference results are robust up to around percent-level precision for the generated neutron star observations, consisting of the mass, equatorial radius, rotation rate, as well as co- and counterrotating $f$-mode frequencies, that enter the framework as data.

Orbital eccentricity and spin precession are precious observables to infer the formation history of binary black holes with gravitational-wave data. We present a post-Newtonian, multi-timescale analysis of the binary dynamics able to capture both precession and eccentricity over long inspirals. We show that the evolution of an eccentric binary can be reduced to that of an effective source on quasicircular orbits, coupled to a post-Newtonian prescription for the secular evolution of the eccentricity. Our findings unveil an interplay between precession and eccentricity: the spins of eccentric binaries precess on shorter timescales and their nutation amplitude is altered compared to black holes on quasicircular orbits, consequently affecting the so-called spin morphology. Even if binaries circularize by the time they enter the sensitivity window of our detectors, their spin orientations retain some memory of the past evolution on eccentric orbits, thus providing a new link between gravitational-wave detection and astrophysical formation. At the same time, we point out that residual eccentricity should be considered a source of systematics when reconstructing the past history of black-hole binaries using the spin orientations.

The evidence of the stochastic gravitational-wave background around the nanohertz frequency range was recently found by worldwide pulsar timing array (PTA) collaborations. One of the cosmological explanations is the gravitational waves induced by enhanced curvature perturbations, but the issue of primordial black hole (PBH) overproduction in this scenario was pointed out in the literature. Motivated by this issue and the ${\mathrm{\Omega }}_{\mathrm{GW}}\sim f^2$ scaling suggested by the data, we study the gravitational waves induced in a cosmological epoch dominated by a stiff fluid ($w=1$) and find that they can safely explain the PTA data well without PBH overproduction.

We study multiple fields inflation in the diffusion-dominated regime using stochastic $\delta N$ formalism. The fields are under pure Brownian motion in a de Sitter background with boundaries in higher-dimensional field space. This setup can be realized toward the final stages of the ultra-slow-roll setup where the classical drifts fall off exponentially and the perturbations are driven by quantum kicks. We consider both symmetric and asymmetric boundaries with absorbing and reflective boundary conditions and calculate the average number of $e$-folds, the first crossing probabilities, and the power spectrum. We study the primordial black holes (PBHs) formation in this setup and calculate the mass fraction and the contribution of PBHs in dark matter energy density for various higher-dimensional field spaces.

Future observations with next-generation large-area radio telescopes are expected to discover radio pulsars (PSRs) closely orbiting around Sagittarius A* (Sgr A*), the supermassive black hole (SMBH) dwelling at our Galactic Center (GC). Such a system can provide a unique laboratory for testing general relativity (GR), as well as the astrophysics around the GC. In this paper, we provide a numerical timing model for PSR-SMBH systems based on the post-Newtonian (PN) equation of motion, and use it to explore the prospects of measuring the black hole (BH) properties with pulsar timing. We further consider the perturbation caused by the dark matter (DM) distribution around Sgr A*, and the possibility of constraining DM models with PSR-SMBH systems. Assuming a 5-year observation of a normal pulsar in an eccentric ($e=0.8$) orbit with an orbital period $P_b=0.5\mathrm{yr}$, we find that—with weekly recorded times of arrival (TOAs) and a timing precision of 1 ms—the power-law index of DM density distribution near the GC can be constrained to about 20%. Such a measurement is comparable to those measurements at the Galactic length scale but can reveal small-scale properties of the DM.

In this study, we employ a convolutional neural network to classify gravitational waves originating from core-collapse supernovae. Training is conducted using spectrograms derived from three-dimensional numerical simulations of waveforms, which are injected onto real noise data from the third observing run of both Advanced LIGO and Advanced Virgo. To gain insights into the decision-making process of the model, we apply class activation mapping techniques to visualize the regions in the input image that are significant for the model’s prediction. The class activation maps reveal that the model’s predictions predominantly rely on specific features within the input spectrograms, namely, the $g$-mode and low-frequency modes. The visualization of convolutional neural network models provides interpretability to enhance their reliability and offers guidance for improving detection efficiency.

We consider a non-self-gravitating geometrically thick torus described by the Weyssenhoff ideal spin fluid in a black hole spacetime. The Weyssenhoff spin fluid shares the same symmetries of the background geometry, i.e., stationarity and axisymmetry and further describes circular orbital motion in the black hole spacetime. We further assume that the alignment of the spin is perpendicular to the equatorial plane. Under this setup, we determine the integrability conditions of the general relativistic momentum conservation equation of Weyssenhoff ideal spin fluid using the Frenkel spin supplementary condition. In light of the integrability conditions, we then present stationary equilibrium solutions of the spin fluid torus with constant specific angular momentum distributions around the Schwarzschild black hole by numerically solving the general relativistic momentum conservation equation. Our study reveals that both the isopressure and isodensity surfaces of torus get significantly modified in comparison to the ideal fluid torus without a spin fluid, owing to the spin tensor and its coupling to the curvature of the Schwarzschild black hole. In fact, the size of the torus is also found to be enhanced (diminished) depending on a positive (negative) magnitude of spin parameter $s_0$. We finally estimate the magnitude of $s_0$ by assuming the torus to be composed of spin-$1/2$ particles.

We present a derivation of quantum kinetic theory for massive spin-1 particles from the Wigner-function formalism up to first order in an $\hslash$-expansion, including a general interaction term. Both local and nonlocal contributions are computed in a covariant fashion. It is shown that, up to first order in $\hslash$, the collision term takes the same form as in the case of spin-$1/2$ particles.

Provided the dark sector consisted of a dark scalar $\varphi$ and a dark fermion $\chi$ under an exact $Z_2$ symmetry, the sterile neutrino $N$ can act as the messenger between the dark sector and standard model via the Yukawa coupling ${\lambda }_{ds}\overline{\chi }\varphi N$. In this paper, we focus on the specific scenario $m_N>m_{\varphi }+m_{\chi }$ with $\chi$ being a feebly interacting massive particle (FIMP) dark matter. The decay width of dark scalar $\varphi$ is doubly suppressed by the smallness of Yukawa coupling ${\lambda }_{ds}$ and mixing angle $\theta$. The delayed decay $\varphi \to \chi \nu$ will have a great impact on cosmological observables such as the big bang nucleosynthesis, the cosmic microwave background anisotropy power spectra, the effective number of relativistic neutrino species $N_{\mathrm{eff}}$ and the energetic neutrino flux. Meanwhile, the sterile neutrino can generate displaced vertex signature at colliders when $m_N<m_W$. The dark scalar $\varphi$ will also induce measurable Higgs invisible decay for relatively large quartic coupling. A comprehensive analysis of constraints from cosmology and collider is performed in this paper. We find that almost the whole parameter space with $m_N<m_W$ is under the reach of future experiments.

We investigate the connection between localization of low-lying Dirac modes and Polyakov-loop ordering in the lattice SU(2) Higgs model at finite temperature, probed with the staggered Dirac operator. After mapping out the phase diagram of the model at a fixed temporal extension in lattice units, we study the localization properties of the low-lying modes of the staggered Dirac operator, how these properties change across the various transitions, and how these modes correlate with the gauge and Higgs fields. We find localized low modes in the deconfined and in the Higgs phase, where the Polyakov loop is strongly ordered, but in both cases they disappear as one crosses over to the confined phase. Our findings confirm the general expectations of the “sea/islands” picture, and the more detailed expectations of its refined version concerning the favorable locations of localized modes, also in the presence of dynamical scalar matter.

We construct the most general disorder operator for SU(N) lattice gauge theory in ($2+1$) dimensions by using exact duality transformations. These disorder operators, defined on the plaquettes and characterized by ($\mathrm{N}-1$) angles, are the creation and annihilation or the shift operators for the SU(N) magnetic vortices carrying $(\mathrm{N}-1)$ types of magnetic fluxes. They are dual to the SU(N) Wilson loop order operators which, on the other hand, are the creation-annihilation or shift operators for the $(\mathrm{N}-1)$ electric fluxes on their loops. The new order-disorder algebra involving SU(N) Wigner D matrices is derived and discussed. The $Z_{\mathrm{N}}(\in \mathrm{SU}(\mathrm{N}))$ ’t Hooft operator is obtained as a special limit. In this limit we also recover the standard Wilson-’t Hooft order-disorder algebra. The partition function representation and the free energies of these SU(N) magnetic vortices are discussed.