We extend the classic results of the paper [P. C. W. Davies, S. A. Fulling, and W. G. Unruh, Phys. Rev. D 13, 2720 (1976).] “Energy-momentum tensor near an evaporating black hole” by considering a massive scalar field in a two dimensions in the presence of a thin shell collapse. We show that outside the shell the WKB approximation is valid for any value of $r$ if $m{r}_g\gg 1$, where $m$ is the mass of the field, and $r_g$ is the Schwarzschild radius. Thus, we use semiclassical modes to calculate the flux in the vicinity of the shell, and at spatial infinity, $r\to +\infty$ at the final stage of the collapse, $t\to +\infty$ with the use of the covariant point-splitting regularization. We get that near the shell and at the spatial infinity the radiation is thermal with Hawking temperature. We obtain the negative flux $T_{vv}$ in the vicinity of the shell, which is similar to the classic result in the massless case.

The existence of quasinormal modes (QNMs) for waves propagating on pure de Sitter space has been called into question in several works. We definitively prove the existence of quasinormal modes for massless and massive scalar fields in all dimensions and for all scalar field masses, and present a simple method for the explicit calculation of QNMs and the corresponding mode solutions. By passing to coordinates that are regular at the cosmological horizon, we demonstrate that certain QNMs only appear in the QNM expansion of the field when the initial data do not vanish near the cosmological horizon. The key objects in the argument are dual resonant states. These are distributional mode solutions of the adjoint field equation satisfying a generalized incoming condition at the horizon, and they characterize the amplitudes with which QNMs contribute to the QNM expansion of the field.

We study scalar, fermionic and gauge fields coupled nonminimally to gravity in the Einstein-Cartan formulation. We construct a wide class of models with nondynamical torsion whose gravitational spectra comprise only the massless graviton. Eliminating nonpropagating degrees of freedom, we derive an equivalent theory in the metric formulation of gravity. It features contact interactions of a certain form between, and among, the matter and gauge currents. We also discuss briefly the inclusion of curvature-squared terms.

We investigate a simple toy model of particle scattering in the flat spacetime limit of an analogue-gravity model. The analogue-gravity medium is treated as a scalar field of phonons that obeys the Klein–Gordon equation and thus admits a Lorentz symmetry with respect to $c_{\mathrm{s}}$, the speed of sound in the medium. The particle from which the phonons are scattered is external to the system and does not obey the sonic Lorentz symmetry that the phonon field obeys. In-universe observers who use the exchange of sound to operationally measure distance and duration find that the external particle appears to be a sonically Lorentz-violating particle. By performing a sonic analogue to Compton scattering, in-universe observers can determine if they are in motion with respect to their medium. If in-universe observers were then to correctly postulate the dispersion relation of the external particle, their velocity with respect to the medium could be found.

The merger rate of primordial black holes depends on their initial clustering. In the absence of primordial non-Gaussianity correlating short and large scales, primordial black holes are distributed à la Poisson at the time of their formation. However, primordial non-Gaussianity of the local type may correlate primordial black holes on large scales. We show that future experiments looking for cosmic microwave background $\mu$ distortion would test the hypothesis of initial primordial black hole clustering induced by local non-Gaussianity, while existing limits already show that significant non-Gaussianity is necessary to induce primordial black hole clustering.

“Axion-CMB scenario” is an interesting possibility to explain the temperature anisotropy of the cosmic microwave background (CMB) by primordial fluctuations of the QCD axion [S. Iso, K. Kawana, and K. Shimada, Phys. Rev. D 102, 103513 (2020)]. In this scenario, fluctuations of radiations are generated by an energy exchange between axions and radiations, which results in the correlation between the primordial axion fluctuations and the CMB anisotropies. Consequently, the cosmological observations stringently constrain a model of the axion and the early history of the universe. In particular, we need a large energy fraction ${\mathrm{\Omega }}_A$ of the axion at the QCD phase transition, but it must become tiny at the present universe to suppress the isocurvature power spectrum. One of natural cosmological scenarios to realize such a situation is the thermal inflation which can sufficiently dilute the axion abundance. Thermal inflation occurs in various models. In this paper, we focus on a classically conformal (CC) $B-L$ model with a QCD axion. In this model, the early universe undergoes a long supercooling era of the $B-L$ and electroweak symmetries, and thermal inflation naturally occurs. Thus it can be a good candidate for the axion-CMB scenario. But the axion abundance at the QCD transition is shown to be insufficient in the original CC $B-L$ model. To overcome the situation, we extend the model by introducing $N$ scalar fields $S$ (either massive or massless) and consider a novel cosmological history such that the $O(N)$ and the $B-L$ sectors evolve almost separately in the early universe. We find that all the necessary conditions for the axion-CMB scenario can be satisfied in some parameter regions for massless $S$ fields, typically $N\sim {10}^{19}$ and the mass of $B-L$ gauge boson around 5–10 TeV.

In this work, we investigate the dynamics of the interacting dark energy and dark matter in viable models of $f(R)$ gravity by using a standard framework of dynamical system analysis. A simple form of the interacting dark energy $Q=3\alpha H{\rho }_m$ is used to study three viable models of $f(R)$ gravity which are consistent with local gravity constraints and satisfying conditions for the cosmological viability. As a result, we find that the fixed points are slightly modified from those obtained in the standard noninteracting analysis of $f(R)$ gravity proposed so far in the literature. In our models of adding this interaction, we find that the dynamical profiles of the Universe in the viable $f(R)$ dark energy models are modified by the interaction term as well as their relevant model parameters. Moreover, our results yield the correct cosmological evolution with additional constraint parameter, $\alpha$, from the interacting dark energy.

Nonthermal acceleration of particles in magnetohydrodynamic (MHD) turbulence plays a central role in a wide variety of astrophysical sites. This physics is addressed here in the context of a strong turbulence, composed of coherent structures rather than waves, beyond the realm of quasilinear theory. The present description tracks the momentum of the particle through a sequence of frames in which the electric field vanishes, in the spirit of the original Fermi scenario. It connects the sources of energy gain (or loss) to the gradients of the velocity of the magnetic field lines, in particular the acceleration and the shear of their velocity flow projected along the field line direction, as well as their compression in the transverse plane. Those velocity gradients are subject to strong intermittency: they are spatially localized, and their strengths obey power law distributions, as demonstrated through direct measurements in the incompressible MHD simulation of the Johns Hopkins University database. This intermittency impacts the acceleration process in a significant way, which opens up prospects for a rich phenomenology. In particular, the momentum distribution, which is here captured through an analytical random walk model, displays extended power law tails with soft-to-hard evolution in time, in general agreement with recent kinetic numerical simulations. Extensions to this description and possible avenues of exploration are discussed.

We study the fit of cosmological models with two additional free parameters $N_{\mathrm{eff}}$ and ${\xi }_e$ in addition to the parameters of $\mathrm{\Lambda }\mathrm{CDM}$. We introduce extra radiation components such as hot axions or sterile neutrinos in addition to the energy density of neutrinos with large neutrino degeneracy. Then, a larger $N_{\mathrm{eff}}$ is allowed without spoiling big bang nucleosynthesis (BBN), as positive neutrino degeneracy ${\xi }_e$ could improve BBN fit. By analysing the data from Planck, baryon acoustic oscillation (BAO), BBN and type-Ia supernovae (SNeIa), it can be seen that the Hubble tension can be ameliorated for ${\xi }_e\simeq 0.04$ and $0.3\lesssim \mathrm{\Delta }{N}_{\mathrm{eff}}\lesssim 0.6$.

Binary neutron star mergers provide a unique probe of the dense-matter equation of state (EoS) across a wide range of parameter space, from the zero-temperature EoS during the inspiral to the high-temperature EoS following the merger. In this paper, we implement a new model for calculating parametrized finite-temperature EoS effects into numerical relativity simulations. This “$M^{*}$-model” is based on a two-parameter approximation of the particle effective mass and includes the leading-order effects of degeneracy in the thermal pressure and energy. We test our numerical implementation by performing evolutions of rotating single stars with zero- and nonzero temperature gradients, as well as evolutions of binary neutron star mergers. We find that our new finite-temperature EoS implementation can support stable stars over many dynamical timescales. We also perform a first parameter study to explore the role of the $M^{*}$ parameters in binary neutron star merger simulations. All simulations start from identical initial data with identical cold EoSs, and differ only in the thermal part of the EoS. We find that both the thermal profile of the remnant and the postmerger gravitational wave signal depend on the choice of $M^{*}$ parameters, but that the total merger ejecta depends only weakly on the finite-temperature part of the EoS across a wide range of parameters. Our simulations provide a first step toward understanding how the finite-temperature properties of dense matter may affect future observations of binary neutron star mergers.

We calculate the absorptive part of the photon polarization tensor in a hot magnetized relativistic plasma. In the derivation, we utilize a Landau-level representation for the fermion Green’s function in a mixed coordinate-momentum space and obtain a closed-form expression for the one-loop polarization tensor. At the leading order in the coupling, its absorptive part is determined by particle and antiparticle splitting processes ($e^{-}\leftrightarrow e^{-}+\gamma$ and $e^{+}\leftrightarrow e^{+}+\gamma$, respectively), as well as by particle-antiparticle annihilation processes ($e^{-}+e^{+}\leftrightarrow \gamma$). The interpretation in terms of quantum transitions between Landau levels is also given. By making use of the photon polarization tensor, we study the differential photon emission rate in the quantum limit of magnetized relativistic plasma. At low energies, the photon emission has a prolate profile with the symmetry axis along the line of the magnetic field. At high energies, on the other hand, the photon emission has an oblate profile. The underlying reasons for such emission profiles are given in both regimes. The general result for the photon polarization tensor is also used to calculate the longitudinal and transverse components of magneto-optical conductivity.

In a previous paper we proposed a new method based on resummations for studying radiation reaction of an electron in a plane-wave electromagnetic field. In this paper we use this method to study the electron momentum expectation value for a circularly polarized monochromatic field with $a_0=1$, for which standard locally constant-field methods cannot be used. We also find that radiation reaction has a significant effect on the induced polarization, as compared to the results without radiation reaction, i.e., the Sokolov-Ternov formula for a constant field, or the zero result for a circularly monochromatic field. We also study the Abraham-Lorentz-Dirac equation using Borel-Padé resummations.

We have developed a covariant isobar model to phenomenologically explain the four possible isospin channels of $K\mathrm{\Sigma }$ photoproduction. To obtain a consistent reaction amplitude, which is free from the lower-spin background problem, we used the consistent electromagnetic and hadronic interactions described in our previous report. We used all available experimental data, including the recent MAMI A2 2018 data obtained for the $K^0{\mathrm{\Sigma }}^{+}$ and $K^0{\mathrm{\Sigma }}^0$ isospin channels. By fitting the calculated observables to these data we extract the resonance properties, including their Breit-Wigner and pole parameters. Comparison of the extracted parameters with those listed by the Particle Data Group yields a nice agreement. An extensive comparison of the calculated observables with experimental data is also presented. By using the model we investigated the effects of three different form factors used in the hadronic vertex of each diagram. A brief discussion on the form factors is given.

The renormalized contribution of fermions to the curvature masses of vector and axial-vector mesons is derived with two different methods at leading order in the loop expansion applied to the ($2+1$)-flavor constituent quark-meson model. The corresponding contribution to the curvature masses of the scalar and pseudoscalar mesons, already known in the literature, is rederived in a transparent way. The temperature dependence of the curvature mass of various (axial-)vector modes obtained by decomposing the curvature mass tensor is investigated along with the (axial-)vector–(pseudo)scalar mixing. All fermionic corrections are expressed as simple integrals that involve at finite temperature only the Fermi-Dirac distribution function modified by the Polyakov-loop degrees of freedom. The renormalization of the (axial-)vector curvature mass allows us to lift a redundancy in the original Lagrangian of the globally symmetric extended linear sigma model, in which terms already generated by the covariant derivative were reincluded with different coupling constants.

Pseudoscalar particles, often referred to as axionlike-particles (ALPs), arise in a variety of theoretical contexts. The phenomenology of such states is typically studied while assuming flavor-conserving interactions, yet they can in principle have flavor-violating (FV) couplings to fermions. We consider this general possibility while focusing on models where the ALP has non-negligible coupling to the Standard Model Higgs boson $h$. For a lepton FV ALP $a$ of mass $m_a\gtrsim 2\mathrm{GeV}$, $a\to \tau \ell$, where $\ell \ne \tau$ is a charged lepton, could have an $\mathcal{O}(1)$ branching fraction, leading to a potentially detectable $h\to aa\to \tau \ell \tau \ell$ at the LHC and its future program. We examine this possibility, in light of existing bounds on FV processes, in a general effective theory. We obtain constraints on the effective couplings from both prompt and long-lifetime searches at the LHC; some projections for envisioned measurements are also provided. The implications of the recently announced first results of the muon $g-2$ measurement at Fermilab for the ALP interactions considered in our work are also briefly discussed.

We consider, in general terms, the possible parameter space of thermal dark matter candidates. We assume that the dark matter particle is fundamental and was in thermal equilibrium in a hidden sector with a temperature $T^{\prime }$, which may differ from that of the Standard Model temperature, $T$. The candidates lie in a region in the $T^{\prime }/T$ vs. $m_{\mathrm{dm}}$ plane, which is bounded by both model-independent theoretical considerations and observational constraints. The former consists of limits from dark matter candidates that decoupled when relativistic (the relativistic floor) and from those that decoupled when nonrelativistic with the largest annihilation cross section allowed by unitarity (the unitarity wall), while the latter concerns big bang nucleosynthesis ($N_{\mathrm{eff}}$ ceiling) and free streaming. We present three simplified dark matter scenarios, demonstrating concretely how each fits into the domain.

In this addendum to the paper by Crivellin and Schnell [Phys. Rev. D 103, 115023 (2021)], we discuss the implications of the recent CMS analysis of lepton flavor universality violation in nonresonant di-lepton pairs for first generation leptoquarks. As CMS finds more electron events than expected from background, this analysis prefers the leptoquark representations ${\tilde{S}}_1,S_2,S_3,{\tilde{V}}_1,V_2({\kappa }_2^{\mathrm{RL}}\ne 0)$ and $V_3$ which lead to constructive interference with the standard model (SM). In principle the excess could also be (partially) explained by the representations ${\tilde{S}}_2,V_1({\kappa }_1^R\ne 0),V_2({\kappa }_2^{\mathrm{LR}}\ne 0),{\tilde{V}}_2$ which are interfering destructively, as this would still lead to the right effect in bins with high invariant mass where the new physics contribution dominates. However, in these cases large couplings would be required which are excluded by other observables. The representations $S_1,V_1({\kappa }_1^L\ne 0)$ cannot improve the fit to the CMS data compared to the SM.

The electromagnetic source of arions, as well as axions, is a scalar product of the magnetic field induction and the electric field intensity. For electromagnetic waves, this product can be nonzero only in the near zone. Pulsars and magnetars are natural sources of this type. Based on these considerations, we calculate the generation of arions by coherent electromagnetic field of rotating magnetic dipole of pulsars and magnetars. It is shown that the radiation of arion waves occurs at the frequency of magnetic dipole rotation. This radiation has a maximum when the angle between the rotation axis and the magnetic dipole moment of the neutron star is $\pi /4$ and it is completely absent, when the magnetic dipole moment is perpendicular or parallel to this axis. A formula for the angular distribution of arion radiation is constructed; and on its basis, it is shown that the radiation is maximal in the plane which is perpendicular to the axis of rotation.

We revisit the possibilities of accommodating the experimental indications of the lepton flavor universality violation in $b$-hadron decays in the minimal scenarios in which the Standard Model is extended by the presence of a single $\mathcal{O}(1\mathrm{TeV})$ leptoquark state. To do so we combine the most recent low energy flavor physics constraints, including $R_{K^{(*)}}^{\exp }$ and $R_{D^{(*)}}^{\exp }$, and combine them with the bounds on the leptoquark masses and their couplings to quarks and leptons as inferred from the direct searches at the LHC and the studies of the large $p_T$ tails of the $pp\to \ell \ell$ differential cross section. We find that none of the scalar leptoquarks of $m_{\mathrm{LQ}}\simeq 1÷2\mathrm{TeV}$ can accommodate the $B$-anomalies alone. Only the vector leptoquark, known as $U_1$, can provide a viable solution which, in the minimal setup, provides an interesting prediction, i.e., a lower bound to the lepton flavor violating $b\to s{\mu }^{\pm }{\tau }^{\mp }$ decay modes, such as $\mathcal{B}(B\to K\mu \tau )\gtrsim 0.7\times {10}^{-7}$.

Motivated by recent attempts to quantum simulate lattice models with continuous Abelian symmetries using discrete approximations, we define an extended-O(2) model by adding a $\gamma \cos (q\phi )$ term to the ordinary O(2) model with angular values restricted to a $2\pi$ interval. In the $\gamma \to \infty$ limit, the model becomes an extended $q$-state clock model that reduces to the ordinary $q$-state clock model when $q$ is an integer and otherwise is a continuation of the clock model for noninteger $q$. By shifting the $2\pi$ integration interval, the number of angles selected can change discontinuously and two cases need to be considered. What we call case 1 has one more angle than what we call case 2. We investigate this class of clock models in two space-time dimensions using Monte Carlo and tensor renormalization group methods. Both the specific heat and the magnetic susceptibility show a double-peak structure for fractional $q$. In case 1, the small-$\beta$ peak is associated with a crossover, and the large-$\beta$ peak is associated with an Ising critical point, while both peaks are crossovers in case 2. When $q$ is close to an integer by an amount $\mathrm{\Delta }q$ and the system is close to the small-$\beta$ Berezinskii-Kosterlitz-Thouless transition, the system has a magnetic susceptibility that scales as $\sim 1/(\mathrm{\Delta }q{)}^{1-1/{\delta }^{\prime }}$ with ${\delta }^{\prime }$ estimates consistent with the magnetic critical exponent $\delta =15$. The crossover peak and the Ising critical point move to Berezinskii-Kosterlitz-Thouless transition points with the same power-law scaling. A phase diagram for this model in the $(\beta ,q)$ plane is sketched. These results are possibly relevant for configurable Rydberg-atom arrays where the interpolations among phases with discrete symmetries can be achieved by varying continuously the distances among atoms and the detuning frequency.