We extend to the Horndeski realm the irreversible thermodynamics description of gravity previously studied in “first generation” scalar-tensor theories. We identify a subclass of Horndeski theories as an out-of–equilibrium state, while general relativity corresponds to an equilibrium state. In this context, we identify an effective heat current, “temperature of gravity,” and shear viscosity in the space of theories. The identification is accomplished by recasting the field equations as effective Einstein equations with an effective dissipative fluid, with Einstein gravity as the equilibrium state, following Eckart’s first-order thermodynamics.

This fourth release of the RIT public catalog of numerical relativity black-hole-binary waveforms consists of 1881 accurate simulations that include 446 precessing and 611 nonprecessing quasicircular/inspiraling binary systems with mass ratios $q=m_1/m_2$ in the range $1/128\le q\le 1$ and individual spins up to $s/m^2=0.95$; and 824 in eccentric orbits in the range $0<e\le 1$. The catalog also provides initial parameters of the binary, trajectory information, peak radiation, and final remnant black hole properties. The waveforms are corrected for the center of mass drifting and are extrapolated to future null infinity. As an application of this waveform catalog we reanalyze all of the peak radiation and remnant properties to find new, simple, correlations among them, valid in the presence of eccentricity, for practical astrophysical usage.

As long-lived quasisolitons from the fragmentation of a scalar condensate, oscillons may dominate the preheating era after inflation. During this period, stochastic gravitational waves can also be generated. We quantify the gravitational-wave production in this period with simulations accounting for full general relativity to capture all possible nonperturbative effects. We compute the gravitational-wave spectra across a range of choices of the oscillon preheating models and compare our results to a conventional perturbative approach on a Friedmann-Lemaître-Robertson-Walker (FLRW) background. We clarify the gauge ambiguities in computing induced gravitational waves from scenarios where dense nonperturbative objects such as oscillons are being formed. In particular, we find that the synchronous gauge tends to contain large artificial enhancements in the gravitational-wave spectrum due to gauge modes if gravity plays an important role in the formation of the oscillons, while other gauge choices, such as the radiation gauge or a suitably chosen “1+log” gauge, can efficiently reduce the contributions of gauge modes. The full general-relativistic simulations indicate that gravitational-wave spectra obtained from the perturbative approach on the FLRW background are fairly accurate, except when oscillon formation induces strong gravitational effects, for which case there can be an order unity enhancement.

We solve coupled momentum-dependent Boltzmann equations for the phase space distribution of cosmic relic particles, without resorting to approximations of assuming kinetic equilibrium or neglecting backscattering or elastic interactions. Our method is amendable to precision numerical computations. To test it, we consider two benchmark models where the momentum dependence of dark matter distribution function is potentially important: a real singlet scalar extension near the Higgs resonance and a sterile neutrino dark matter model with a singlet scalar mediator. The singlet scalar example shows that the kinetic equilibrium may hold surprisingly well even near sharp resonances. However, the integrated method may underestimate the relic density by up to 40% in extreme cases. In the sterile neutrino dark matter model, we studied how the inclusion of previously ignored elastic interactions and processes with initial state sterile neutrinos could affect the nonthermal nature of their resulting distributions. Here the effects turned out to be negligible, proving the robustness of the earlier predictions.

According to quantum electrodynamics (QED), a strong electromagnetic field can make the vacuum state decay via the production of electron-positron pairs. Here we investigate the emission of soft photons which accompanies a nonperturbative process of pair production. Our analysis is carried out within the Furry picture to first order in the fine-structure constant. Also, it is shown that the presence of photons in the initial state gives rise to an additional (stimulated) channel of photon emission besides the pure vacuum one. On the other hand, the number of final (signal) photons includes also a negative contribution due to photon absorption within the pair production process. These contributions are evaluated and compared. To obtain quantitative predictions in the domain of realistic field parameters, we employ the Wentzel-Kramers-Brillouin approach. We propose using an optical-probe photon beam, whose intensity changes as it traverses a spatial region where a strong electric component of a background laser field is present. It is demonstrated that relative intensity changes on the level of 1% can be experimentally observed once the intensity of the strong background field exceeds ${10}^{27}{\mathrm{W}/\mathrm{cm}}^2$ within a large laser-wavelength interval. This finding is expected to significantly support possible experimental investigations of nonlinear QED phenomena in the nonperturbative regime.

A two-component scalar dark matter scenario comprising an additional scalar doublet and a $Y=0$ scalar triplet is proposed. Key features of the ensuing dark matter phenomenology are highlighted with emphasis on interconversion between the two dark matter components. For suitable choices of the model parameters, we show that such interconversion can explain the observed relic abundance when the doublet dark matter component has mass in the desert region while the triplet component has sub-TeV mass. This finding is important in the context of such mass regions known to predict underabundant relic density for the stand-alone cases of the scalar doublet and triplet. In addition, we also show that the present scenario can stabilize the electroweak vacuum up to the Planck scale in the parameter space responsible for the requisite dark matter observables.

We survey a set of proposed light-front models for confinement in the valence quark sector of the mesons and portray similarities as well as differences. We present the spectroscopies for the light mesons that result from a selection of longitudinal confinement forms. We note that the Sturm-Liouville theory provides a unifying framework for many elements of this comparison.

In perturbative thermal calculations, introducing nonzero quark masses causes considerable complications. In this article we describe an approximation scheme valid for sufficiently light masses which significantly simplifies the relevant calculations with only a small loss in accuracy. We apply the scheme to quantum chromodynamics, with two massless and one massive flavor, obtaining analytic results which are in excellent agreement with numerical nonapproximated results. Our results are accurate to $O(g^5)$ in the strong coupling parameter $g$, as long as either the chemical potential $\mu$ of the quark species with nonzero mass $m$ satisfies $m=O(g\mu )$ or if the temperature $T$ satisfies $m=O(gT)$. We find that these conditions are always satisfied for the three lightest quarks for the values of $\mu$, $T$ where quantum chromodynamics is perturbatively convergent.

In this work, we study the $1^{--}$ double-gluon charmonium ($\overline{c}ggc$) and bottomonium ($\overline{b}ggb$) hybrids in terms of QCD sum rules. We find that the mass of $\overline{c}ggc$ hybrid lies in $M_{H_c}=5.33–5.90\mathrm{GeV}$, while in the bottom sector the mass of $\overline{b}ggb$ hybrid may be situated in $M_{H_b}=11.20–11.68\mathrm{GeV}$. The contributions up to dimension eight at leading order of ${\alpha }_s$ (LO) in the operator product expansion are taken into account in the calculation. The double-gluon charmonium hybrid meson predicted in this work can decay into a pair of charmed mesons or a pair of charmed mesons together with a light meson. Especially, we propose to search for $\overline{c}ggc$ hybrid with $I^G(J^{PC})=0^{-}(1^{--})$ in their decay channels $D\overline{D}/D^{*}\overline{D}/D^{*}{\overline{D}}^{*}$ with P wave and $D^{*}{\overline{D}}^{*}\pi /D^{*}{\overline{D}}^{*}\eta /D\overline{D}\rho /D\overline{D}\omega$ with S wave, which may be accessible in Belle II, PANDA, Super-B, GlueX, and LHCb experiments.

The static properties, masses, and decay constants, of a pseudoscalar meson triplet in a strongly magnetized medium are studied through the Dyson-Schwinger equation approach treatment of a contact interaction. Complementary to the usual vector-vector form, a symmetry-preserving formulation of couplings has been proposed in this work, without modifying the quark propagator, to control the strength of the $p$-wave component of Bethe-Salpeter amplitude. It is found that, with the help of flexible auxiliary interaction, our simple model is able to reproduce the observation in the lattice QCD simulation, where the spectra of the charged pseudoscalar meson shows a nonmonotonic behavior as the magnetic field grows. The results of this work imply that the strong magnetic field affects the inner structure of mesons dramatically.

The island formula—an extremization prescription for generalized entropy—is known to result in a unitary Page curve for the entropy of Hawking radiation. This semiclassical entropy formula has been derived for Jackiw-Teitelboim (JT) gravity coupled to conformal matter using the “replica trick” to evaluate the Euclidean path integral. Alternatively, for eternal Anti–de Sitter black holes, we derive the extremization of generalized entropy from minimizing the microcanonical action of an entanglement wedge. The on-shell action is minus the entropy and arises in the saddle-point approximation of the (nonreplicated) microcanonical path integral. When the black hole is coupled to a bath, islands emerge from maximizing the entropy at fixed energy, consistent with the island formula. Our method applies to JT gravity as well as other two-dimensional dilaton gravity theories.

The timelike and null-like geodesics around compact objects are some of the best tools to classify and understand the structure of a space-time. We study the null geodesics around charged static dilaton black holes in Einstein-Maxwell-dilaton gravity. The physical parameters for nonradial geodesics, including the effective potential, effective force, radius of the photon sphere, and impact parameter, are obtained, and effects of the charge parameter and dilaton coupling constant on these quantities are studied. Possible photon motions for different values of the impact parameter are analyzed, and unstable circular orbits and unbounded orbits are plotted. These results are compared to that of Schwarzschild, Reissner-Nordström, and Gibbons-Maeda-Garfinkle-Horowitz-Strominger black holes. Also, we study the shadow cast by a dilaton black hole and investigate how the dilaton coupling affects the size of the black hole shadow. Finally, as an application of null geodesics, we calculate the deflection of light and investigate the effects of the model parameters on the bending angle.

Old minimal $R+R^2$ supergravity has a $U(1)$ $R$ symmetry which rotates the chiral curvature superfield. We gauge this $R$ symmetry and study new interactions involving the gauge multiplet in the context of inflation and supersymmetry breaking. We construct models where supersymmetry and the $R$ symmetry are spontaneously broken during and after Starobinsky inflation, and one-loop gauge anomalies are canceled by the Green–Schwarz mechanism which can also generate Standard Model gaugino masses. The hierarchy between the auxiliary fields, $⟨F⟩\gtrsim ⟨D⟩$, leads to split mass spectrum where the chiral multiplet masses are around the inflationary scale (${10}^{13}\mathrm{GeV}$), while the gauge multiplet masses can be arbitrarily small.

Continuous gravitational waves represent one of the long-sought types of signals that have yet to be detected. Due to their small amplitude, long observational datasets (months–years) have to be analyzed together, thereby vastly increasing the computational cost of these searches. All-sky searches face the most severe computational obstacles, especially searches for sources in unknown binary systems, which need to break the data into very short segments in order to be computationally feasible. In this paper, we present a new detection statistic that improves sensitivity by up to 19% compared to the standard $\mathcal{F}$-statistic for segments shorter than a few hours.

In this paper we consider a problem of formation and evolution of orbital parameters of a binary primordial black hole (PBH) due to gravitational interaction with clustering cold dark matter (CDM). Mass and initial separation have values, which are appropriate for the problem of explanation of the LIGO/Virgo events by coalescing binary PBHs. We consider both radiation dominated and CDM dominated stages of the evolution using numerical and semianalytical means. We show that at the end time of our numerical simulations binary’s semimajor axis decreases by approximately one hundred times, while its angular momentum decreases by ten times, in comparison to the standard values, which do not take into account effects associated with CDM clustering. We check that our conclusions are hardly affected by numerical artefacts. We estimate the merger rate of binary PBHs due to emission of gravitational wave at the present time both in the standard case when the effects associated with clustering are neglected and in the case when they are taken into account and show, that these effects could increase the merger rate at least by 6–8 times in comparison to the standard estimate. This, in turn, means, that a mass fraction of PBHs, $f$, should be smaller than it was assumed before.

The stability and equation of state of quark matter are studied within both two-flavor and ($2+1$)-flavor Nambu-Jona-Lasinio (NJL) models including the vector interactions. With a free parameter $\alpha$, the Lagrangian is constructed by two parts, the original NJL Lagrangian and the Fierz transformation of it, as $\mathcal{L}=(1-\alpha ){\mathcal{L}}_{\mathrm{NJL}}+\alpha {\mathcal{L}}_{\text{Fierz}}$. We find that there is a possibility for both $ud$ nonstrange and $uds$ strange matter being absolute stable, depending on the interplay of the confinement with quark vector interaction and the exchange interaction channels. The calculated quark star properties can reconcile with the recently measured masses and radii of PSR $\mathrm{J}0030+0451$ and PSR $\mathrm{J}0740+6620$, as well as the tidal deformability of GW170817. Furthermore, the more strongly interacting quark matter in the nonstrange stars allows a stiffer equation of state and consequently a higher maximum mass ($\sim 2.7M_{\odot }$) than the strange ones ($\sim 2.1M_{\odot }$). The sound velocities in strange and nonstrange quark star matter are briefly discussed compared to those of neutron star matter.

Fast neutrino flavor conversion can occur in core-collapse supernovae or compact binary merger remnants when nonforward collisions are also at play, and neutrinos are not fully decoupled from matter. This work aims to shed light on the conditions under which fast flavor conversion is enhanced or suppressed by collisions. By relying on a neutrino toy model with three angular bins in the absence of spatial inhomogeneities, we consider two angular configurations: The first one with angular distributions of ${\nu }_e$ and ${\overline{\nu }}_e$ that are almost isotropic as expected before complete neutrino decoupling and showing little flavor conversion when collisions are absent. The second one with angular distributions of ${\nu }_e$ and ${\overline{\nu }}_e$ that are forward peaked as expected in the free-streaming regime and showing significant flavor conversion in the absence of collisions. By including angle-independent, direction-changing collisions, we find that collisions are responsible for an overall enhancement (damping) of flavor conversion in the former (latter) angular configuration. These opposite outcomes are due to the nontrivial interplay between collisions, flavor conversion, and the initial angular distributions of the electron type neutrinos. The enhancement in neutrino flavor conversion is found to be anticorrelated with the magnitude of flavor conversions in the absence of collisions.

The MUonE experiment will provide a precise measurement of the hadronic vacuum polarization contribution to $(g-2{)}_{\mu }$ via ${\mu }^{-}{e}^{-}\to {\mu }^{-}{e}^{-}$. Exploiting the process ${\mu }^{-}N\to {\mu }^{-}NX$, with $N$ the target nucleus and $X$ a new physics light mediator, MUonE can be sensitive to new regions of parameter space for sub-GeV dark photons. In particular, thanks to its muon beam, MUonE will explore uncharted parameter space regions for the $L_{\mu }-L_{\tau }$ model. Finally, MUonE can probe axionlike particles for different assumptions of their couplings to electrons, muons, and photons.

We present a generalization of the string’s Polyakov action that describes a conformally invariant four-dimensional brane. The new extended object is very different from the traditional D-branes of string theory, but, nevertheless, shares some structural similarities with the string, especially when it comes to the low-energy limit of small tension. We introduce a rather rich structure of tensors that can play a role at low energies. In analogy with the bosonic string, we initiate the quantization of the new brane discussing the extent in which it produces a critical dimension of spacetime and Einstein’s equations coupled to a scalar dilaton under some approximations.

We generalize the Unruh-DeWitt detector model to second quantization. We illustrate this model by applying it to an excited particle in a superposition of relativistic velocities. We calculate, to first order, how its decay depends on whether its superposition of velocities is coherent or incoherent. Further, we generalize the framework of quantum reference frames to allow transformations to the rest frames of second-quantized Unruh DeWitt detectors. As an application, we show how to transform into the rest frame of a decaying particle that, in the laboratory frame, is in a linear superposition of relativistically differing velocities.