We propose a three-flavor version of the Polyakov-Nambu-Jona-Lasino (PNJL) model at zero temperature regime, by implementing a traced Polyakov loop ($\mathrm{\Phi }$) dependence in the scalar, vector and ’t Hooft channel strengths. We study the thermodynamics of this model, named as PNJL0, with special attention for the first-order confinement/deconfinement phase transition for which $\mathrm{\Phi }$ is the order parameter. For the symmetric quark matter case, an interesting feature observed is a strong reduction of the constituent strange quark mass ($M_s$) at the chemical potential related to point where deconfinement takes place. The emergence of $\mathrm{\Phi }$ favors the restoration of chiral symmetry even for the strange quark. We also investigate the charge neutral system of quarks and leptons in weak equilibrium. As an application, we construct a hadron-quark phase transition with a density dependent hadronic model coupled to the SU(3) PNJL0 model. In this case, the quark side is composed by deconfined particles. This approach is used to determine mass-radius profiles compatible with recent data from the Neutron Star Interior Composition Explorer mission.

We study the doubly heavy baryon ${\mathrm{\Xi }}_{cc}$ production in $\mathrm{\Upsilon }(1S)$ decay. The nonrelativistic framework is employed to describe the bound states for the calculation on the partial width. It is shown that the corresponding branching ratio can be significant and can be well measured as the $\mathrm{\Upsilon }(1S)$ decay to $J/\mathrm{\Psi }+c\overline{c}+\text{anything}$ process.

We consider the loop quantum theory of the spherically symmetric model of gravity coupled to Gaussian dust fields, where the Gaussian dust fields provide a material reference frame of the space and time to deparametrize gravity. This theory, used to study the quantum features of the spherically symmetric BH, is constructed based on a 1-dimensional lattice $\gamma \subset \mathbb{R}$. Taking advantage of the path integral formulation, we investigate the quantum dynamics and obtain an effective action. With this action, we get an effective continuous description of this quantum lattice system which is not the same as the one described by the effective Hamiltonian used in [M. Han and H. Liu, Improved effective dynamics of loop-quantum-gravity black hole and Nariai limit], i.e., the classical Hamiltonian with the holonomy correction. It turns out that, the Hamiltonian derived in this paper can return to that used in [M. Han and H. Liu] only for macro black holes, since the lattice $\gamma$ is required to be sufficiently fine. Indeed, it is necessary to propose this fine-grained lattice structure in order to well describe the underlying lattice theory by the continuous description.

In a holographic model, which was used to investigate the color superconducting phase of QCD, a dilute gas of instantons is introduced to study the nuclear matter. The free energy of the nuclear matter is computed as a function of the baryon chemical potential in the probe approximation. Then the equation of state is obtained at low temperature. Using the equation of state for the nuclear matter, the Tolman-Oppenheimer-Volkov equations for a cold compact star are solved. We find the mass-radius relation of the star, which is similar to the one for the quark star. This similarity implies that the instanton gas given here is a kind of self-bound matter.

In this article we study the Conrady-Hnybida extension of the Lorentzian Engle-Pereira-Rovelli-Livine spin-foam model, which admits timelike cells rather than just spacelike ones. Our focus is on the asymptotic analysis of the model’s vertex amplitude. We propose a new parametrization for states associated to timelike 3-cells, from which we derive a closed-form expression for their amplitudes. This allows us to revisit the conditions under which critical points of the amplitudes occur, and we find Regge-like geometrical critical points in agreement with the literature. However, we find also evidence for nongeometrical points which are not dynamically suppressed without further assumptions; the model then does not strictly asymptote to the Regge action, contrary to what one would expect. We moreover prove Minkowski and rigidity theorems for Minkowskian polyhedra, extending the asymptotic analysis to nonsimplicial spin-foams.

In this work, we use the framework of effective field theory to couple Einstein’s gravity to quantum electrodynamics (QED) and determine the gravitational corrections to the two-loop beta function of the electric charge in arbitrary electrodynamics (Lorentz-like) and arbitrary (de Donder–like) gravitational gauges. Our results indicate that gravitational corrections do not alter the running behavior of the electric charge; on the contrary, we observe that it gives a positive contribution to the beta function, making the electric charge grow even faster.

Obtaining black hole solutions in alternative theories of gravity can be a difficult task due to cumbersome field equations that arise in many of such theories. In order to study the strong field regime in a model-free approach, one can consider deformed black hole solutions with additional parameters beyond mass, charge and angular momentum. We investigate the scattering and absorption of a massless scalar field by non-Schwarzschild black holes, considering the Johannsen and Psaltis parametrization. In particular, we study the scattering process by the classical (null geodesics analysis), semiclassical (glory approximation) and partial waves approaches. We present the formalism needed to compute the scattering and absorption of massless scalar waves by Schwarzschild-like black holes with a set of deformation parameters in addition to their mass and present a selection of our results. We compare our numerical results for the scattering cross section with the classical and semiclassical results, obtaining excellent agreement.

We consider isotropic and monochromatic photon emissions from equatorial emitters moving along future-directed timelike geodesics in the near-horizon extremal Kerr (NHEK) and near-horizon near-extremal Kerr (near-NHEK) regions, to asymptotic infinity. We obtain numerical results for the photon escaping probability (PEP) and derive analytical expressions for the maximum observable blueshift (MOB) of the escaping photons, both depending on the emission radius and the emitter’s proper motion. In particular, we find that for all antiplunging or deflecting emitters that can eventually reach to asymptotic infinity, the PEP is greater than 50% while for all plunging emitters the PEP is less than 55%, and for the bounded emitters in the (near-)NHEK region, the PEP is always less than 59%. In addition, for the emitters on unstable circular orbits in the near-NHEK region, the PEP decreases from 55% to 50% as the orbital radius decreases from the one of the innermost stable circular orbit to the one of the horizon. Furthermore, we show how the orientation of the emitter’s motion along the radial or azimuthal direction affects the PEP and the MOB of the emitted photons.

An exact Kerr-like solution has been obtained recently in Einstein-bumblebee gravity model where Lorentz symmetry is spontaneously broken. In this paper, we investigate the superradiant instability of the Kerr-like black hole under the perturbation of a massive scalar field. We find the Lorentz breaking parameter $L$ does not affect the superradiance regime or the regime of the bound states. However, since $L$ appears in the metric and its effect cannot be erased by redefining the rotation parameter $\tilde{a}=\sqrt{1+L}a$, it indeed affects the bound state spectrum and the superradiance. We calculate the bound state spectrum via the continued-fraction method and show the influence of $L$ on the maximum binding energy and the damping rate. The superradiant instability could occur since the superradiance condition and the bound state condition could be both satisfied. Compared with Kerr black hole, the nature of the superradiant instability of this black hole depends nonmonotonously not only on the rotation parameter of the black hole $\tilde{a}$ and the product of the black hole mass $M$ and the field mass $\mu$, but also on the Lorentz breaking parameter $L$. Through the Monte Carlo method, we find that for the $l=m=1$ state the most unstable mode occurs at $L=-0.79637$, $\tilde{a}/M=0.99884$, and $M\mu =0.43920$, with the maximum growth rate of the field ${\omega }_{I}M=1.676\times {10}^{-6}$, which is about 10 times than that in the Kerr black hole.

Herein, we extend Joule-Thomson expansion to the low-dimensional regime by considering the rotating Bañados-Teitelboim-Zanelli (BTZ) metric in the ($2+1$)-dimensional space-time. Specifically, the properties of three important aspects of the Joule-Thomson expansion, including the Joule-Thomson coefficient, inversion curve, and isenthalpic curve were studied. The divergence point of the Joule-Thomson coefficient and the zero point of the Hawking temperature were investigated. The inversion temperature and isenthalpic curves in the $T–P$ plane were obtained, and the cooling-heating regions were determined. Furthermore, the minimum inversion temperature was found to be zero, and the black hole becomes an extremal black hole. The ratio of the minimum inversion and critical temperatures for BTZ black holes does not exist, since the BTZ black hole does not exhibit the critical behavior in the critical pressure $P_c$, critical temperature $T_c$, and critical volume $V_c$.

The computational cost of inspiral and merger simulations for black hole binaries increases in inverse proportion to the square of the mass ratio $q≔m_2/m_1\le 1$. One factor of $q$ comes from the number of orbital cycles, which is proportional to $1/q$, and another is associated with the required number of time steps per orbit, constrained (via the Courant-Friedrichs-Lewy condition) by the need to resolve the two disparate length scales. This problematic scaling makes simulations progressively less tractable at smaller $q$. Here we propose and explore a method for alleviating the scale disparity in simulations with mass ratios in the intermediate astrophysical range (${10}^{-4}\lesssim q\lesssim {10}^{-2}$), where purely perturbative methods may not be adequate. A region of radius much larger than $m_2$ around the smaller object is excised from the numerical domain, and replaced with an analytical model approximating a tidally deformed black hole. The analytical model involves certain a priori unknown parameters, associated with unknown bits of physics together with gauge-adjustment terms; these are dynamically determined by matching them to the numerical solution outside the excision region. In this paper we develop the basic idea and apply it to a toy model of a scalar charge in a circular-geodesic orbit around a Schwarzschild black hole, solving for the massless Klein-Gordon field in a $(1+1)\mathrm{D}$ framework. Our main goal here is to explore the utility and properties of different matching strategies, and to this end we develop two independent implementations, a finite-difference one and a spectral one. We discuss the extension of our method to a full 3D numerical evolution and to gravity.

We study the spontaneous excitation of a two-level atom in the presence of a perfectly reflecting mirror, when the atom, or the mirror, is uniformly accelerating in the framework of the generalized uncertainty principle (GUP). The quantized scalar field obeys a modified dispersion relation leading to a GUP deformed Klein-Gordon equation. The solutions of this equation with suitable boundary conditions are obtained to calculate the spontaneous excitation probability of the atom for the two separate cases. We show that in the case when the mirror is accelerating, the GUP modulates the spatial oscillation of the excitation probability of the atom, thus breaking the symmetry between the excitation of an atom accelerating relative to a stationary mirror, and a stationary atom excited by an accelerating mirror. An explicit violation of the equivalence principle seems to be thus manifested. We further obtain an upper bound on the GUP parameter using standard values of the system parameters.

In this work, we consider four $f(R)$ gravity models—the Hu-Sawicki, Starobinsky, Exponential and Tsujikawa models—and use a range of cosmological data, together with Markov Chain Monte Carlo sampling techniques, to constrain the associated model parameters. Our main aim is to compare the results we get when ${\mathrm{\Omega }}_{k,0}$ is treated as a free parameter with their counterparts in a spatially flat scenario. The bounds we obtain for ${\mathrm{\Omega }}_{k,0}$ in the former case are compatible with a flat geometry. It appears, however, that a higher value of the Hubble constant $H_0$ allows for more curvature. Indeed, upon including in our analysis a Gaussian likelihood constructed from the local measurement of $H_0$, we find that the results favor an open universe at a little over $1\sigma$. This is perhaps not statistically significant, but it underlines the important implications of the Hubble tension for the assumptions commonly made about spatial curvature. We note that the late-time deviation of the Hubble parameter from its $\mathrm{\Lambda }\mathrm{CDM}$ equivalent is comparable across all four models, especially in the nonflat case. When ${\mathrm{\Omega }}_{k,0}=0$, the Hu-Sawicki model admits a smaller mean value for ${\mathrm{\Omega }}_{\mathrm{cdm},0}{h}^2$, which increases the said deviation at redshifts higher than unity. We also study the effect of a change in scale by evaluating the growth rate at two different wave numbers $k_{†}$. Any changes are, on the whole, negligible, although a smaller $k_{†}$ does result in a slightly larger average value for the deviation parameter $b$.

In this work, we study tracker phantom dark energy models with a general parametrization of the scalar potentials. Our analysis also considers the scenario of having both phantom field and the cosmological constant as the dark energy components. A detailed statistical analysis with current cosmological observations shows an increase in the value of the Hubble parameter due to the presence of phantom dark energy but it cannot alleviate the Hubble tension completely. Our results using Bayesian methods suggest a decisive evidence in favor of a phantom field over a positive cosmological constant, although the possibility of a negative cosmological constant cannot be ruled out, hidden in the dark sector.

We demonstrate that cosmic string loops may provide a joint resolution of two mysteries surrounding recently observed black holes. For a string tension in an appropriate range, large radius string loops have the potential to provide the nonlinearities in the early universe that seed supermassive black holes. The more numerous smaller radius string loops can then seed intermediate mass black holes, including those with a mass in the region between $65M_{\odot }$ and $135M_{\odot }$ in which standard black hole formation scenarios predict no black holes are able to form, but which have recently been detected by the LIGO/VIRGO Collaboration. We find that there could be as many as ${10}^6$ of intermediate mass black holes per galaxy, providing a tantalizing target for gravitational wave observatories to look for.

We study the quiescent luminosities of accreting neutron stars by a new mechanism as neutrino heating for additional deep crustal heating, where the neutrino heating is produced by charged pions decay from the nuclear collisions on the surface of neutron star during its active accretion. For low mass neutron star ($\lesssim 1.4M_{\odot }$), as the neutrino heating is little ($\lesssim 1\mathrm{MeV}$ per accreted nucleon) or there would be no neutrino heating, the quiescent luminosity will be not affected or slightly affected. While for massive neutron star ($\gtrsim 2M_{\odot }$), the quiescent luminosity will be enhanced more obviously with neutrino heating in the range 2–6 MeV per accreted nucleon. The observations on cold neutron stars such as 1H $19605+00$, SAX J1808.4-3658 can be explained with neutrino heating if a fast cooling and heavy elements surface are considered. The observations on a hot neutron star such as RX J0812.4-3114 can be explained with neutrino heating if the direct Urca process is forbidden for a massive star with light elements surface, which is different from the previous work that the hot observations should be explained with small mass neutron star and the effect of superfluidity.

Numerous particle models for the cosmological dark matter feature a pair-annihilation rate that scales with powers of the relative velocity between the annihilating particles. As a result, the annihilation rate in the central regions of a dark matter halo can be significantly lower than at the halo’s periphery for particular ambient gravitational potentials. While this might be offset by an increasing dark matter pair number density in the inner halo, it raises the question; what angular region for dark matter models with velocity-suppressed annihilation rates optimizes the signal to noise ratio? Here, we consider simplified background models for galactic and extragalactic targets and demonstrate that the optimal observing strategy varies greatly case by case. Generally, a bright central source warrants an annular region of interest, while a flatter background warrants as large as possible an angular region, possibly including the central regions.

Universal relations that are independent of the equation of state (EOS) for neutron star matter are valuable, if they exist, for extracting the neutron star properties, which generally depend on the EOS. In this study, we newly derive the universal relations predicting the gravitational wave frequencies for the fundamental ($f$), the 1st pressure ($p_1$), and the 1st spacetime ($w_1$) modes and the damping rate for the $f$- and $w_1$-modes as a function of the dimensionless tidal deformability. In particular, with the universal relations for the $f$-modes one can predict the frequencies and damping rate with less than 1% accuracy for canonical neutron stars.

The energy spectra of primary and secondary cosmic rays (CRs) generally harden at several hundreds of GeV, a finding which can be naturally interpreted by means of propagation effects. We adopt a spatially dependent CR propagation model to fit the spectral hardening, where a slow-diffusion disk (SDD) is assumed near the galactic plane. We aim to constrain the propagation parameters with a Bayesian parameter estimation based on a Markov chain Monte Carlo sampling algorithm. The latest precise measurements of carbon spectrum and B/C ratio are adopted in the Bayesian analysis. The ${}^{10}\mathrm{Be}/{}^9\mathrm{Be}$ and Be/B ratios are also included to break parameter degeneracies. The fitting result shows that all the parameters are well constrained. Especially, the thickness of the SDD is limited to 0.4–0.5 kpc above and below the galactic plane, which could be the best constraint for the slow-diffusion region among similar works. The $\overline{p}/p$ ratio and the amplitude of CR anisotropy predicted by the SDD model are consistent with the observations, while the predicted high-energy electron and positron fluxes are slightly and significantly lower than the observations, respectively, indicating the necessity of extra sources.

Combining the multilepton searches at the LHC, we study the possibilities of accommodating the new data of muon and electron $g-2$ anomalies in the lepton-specific inert two-Higgs-doublet model. We take the heavy $CP$-even Higgs as the 125 GeV Higgs, and find the muon and electron $g-2$ anomalies can be explained simultaneously in the region of $5\mathrm{GeV}<m_h<60\mathrm{GeV}$, $200\mathrm{GeV}<m_A<620\mathrm{GeV}$, $190\mathrm{GeV}<m_{H^{\pm }}<620\mathrm{GeV}$ for appropriate Yukawa couplings between leptons and inert Higgs. Meanwhile, the model can give a better fit to the data of lepton universality in $\tau$ decays than the SM. Further, the multilepton event searches at the LHC impose a stringent upper bound on $m_h$, $m_h<35\mathrm{GeV}$.