The explicit expression for the photon polarization operator in the presence of a single electron is found in the $in-in$ formalism in the one-loop approximation out of the photon mass shell. This polarization operator describes the dielectric permittivity of a single electron wave packet in coherent scattering processes. The plasmons and plasmon-polaritons supported by a single electron wave packet are described. The two limiting cases are considered: the wavelength of the external electromagnetic field is much smaller than the typical scale of variations of the electron wave packet and the wavelength of the external electromagnetic field is much larger than the size of the electron wave packet. In the former case, there are eight independent plasmon-polariton modes. In the latter case, the plasmons boil down to the dynamical dipole moment attached to a point electron. Thus, in the infrared limit, the electron possesses a dynamical electric dipole moment manifesting itself in coherent scattering processes.

Building upon Zubarev’s nonequilibrium statistical operator formalism, we derive a relativistic canonical-like second-order spin hydrodynamics for two power-counting schemes. We obtain comprehensive second-order expressions for dissipative fluxes, including the shear stress tensor, bulk viscous pressure, charge-diffusion currents, rotational stress tensor, boost heat vector, and spin tensor-related dissipative flux. By introducing novel transport coefficients and expressing them in terms of equilibrium correlation functions, we establish new Kubo-type formulas for second-order transport. Our findings have significant implications for understanding the collective spin dynamics of strongly interacting matter and provide a robust theoretical basis for future experimental and theoretical studies.

The salient feature of both classical and quantum gravity is its universal and attractive character. However, less is known about the behavior and build-up of quantum correlations when quantum systems interact via graviton exchange. In this work, we show that quantum correlations can remain strongly suppressed for certain choices of parameters even when considering two adjacent quantum systems in delocalized states. Using the framework of linearized quantum gravity with post-Newtonian contributions, we find that there are special values of delocalization where gravitationally induced entanglement drops to negligible values, albeit nonvanishing. We find a pronounced cancellation point far from the Planck scale, where the system tends toward classicalization. In addition, we show that quantum correlations begin to reemerge for large and tiny delocalizations due to Heisenberg’s uncertainty principle and the universal coupling of gravity to the energy-momentum tensor, forming a valley of gravitational entanglement.

Vacuum polarization is numerically investigated for the interaction between a GeV electron beam and a counterpropagating ultraintense laser pulse in the quantum radiation-dominated regime. We identify a signal of vacuum polarization in pair density using a straightforward one-stage setup, circumventing the challenge of preparations of highly polarized probe photons or precise measurements of photon polarization. In our scheme, most electrons are scattered in the direction of laser propagation while emitting substantial linearly polarized gamma photons. These photons undergo vacuum birefringence and dichroism before decaying into electron-positron pairs via the nonlinear Breit-Wheeler process. We demonstrate that vacuum dichroism enhances the purity of linear polarization, which suppresses the overall yield of electron-positron pairs and allows energetic photons to penetrate deeper into the laser pulse. The pairs produced by these energetic photons are more likely to be deflected into small-angle regions rather than being reflected, leading to an enhancement of pair yield in forward scattering. The difference in positron yield may have potential applications in measuring vacuum polarization effect in future laser-particle experiments.

We calculate the gravitational waves (GWs) produced by primordial black holes (PBHs) in the presence of the inflaton condensate in the early Universe. Combining the GW production from the evaporation process, the gravitational scattering of the inflaton itself, and the density fluctuations due to the inhomogeneous distribution of PBHs, we propose for the first time a complete coherent analysis of the spectrum, revealing three peaks, one for each source. Three frequency ranges ($\sim \mathrm{kHz}$, GHz, and PHz, respectively) are expected, each giving rise to a similar GW peak amplitude ${\mathrm{\Omega }}_{\mathrm{GW}}$. We also compare our predictions with current and future GWs detection experiments.

We have investigated the late-time asymptotic solutions, attractor, and focusing behavior of minimal causal spin hydrodynamics in Bjorken expansion. Using the method of dominant balance, we derive the late-time asymptotic solutions of the evolution equation for spin density and identify the specific conditions necessary for the spin density to exhibit a power-law decay. We then analyze both the late-time and early time attractors for the decay rate of spin density. Additionally, we report the focusing behavior in spin hydrodynamics, which has not been found in conventional relativistic hydrodynamics in Bjorken expansion. Our findings suggest that spin density can be treated as a conventional hydrodynamic variable at late times under certain conditions.

We consider spin polarization of massless fermions in a shear flow, whose complete contributions contain magnetization current and side-jump current known from collisional chiral kinetic theory. We argue that the side-jump current adopts interpretation of displacement current. We explicitly determine the displacement current contribution in the steady state reached in shear flow for a quantum electrodynamics (QED) plasma. We find the displacement contribution enhances the magnetization contribution at small and large momenta, but leads to a suppression effect at intermediate momenta. Major differences from previous studies on collisional effect are (i) the fermions are in the same steady state as the medium rather than being probes; (ii) Compton scattering and pair annihilation are also included in addition to the Coulomb scattering considered before.

Self-supervised learning (SSL) is at the core of training modern large machine learning models, providing a scheme for learning powerful representations that can be used in a variety of downstream tasks. However, SSL strategies must be adapted to the type of training data and downstream tasks required. We propose resimulation-based self-supervised representation learning (RS3L), a novel simulation-based SSL strategy that employs a method of resimulation to drive data augmentation for contrastive learning in the physical sciences, particularly, in fields that rely on stochastic simulators. By intervening in the middle of the simulation process and rerunning simulation components downstream of the intervention, we generate multiple realizations of an event, thus producing a set of augmentations covering all physics-driven variations available in the simulator. Using experiments from high-energy physics, we explore how this strategy may enable the development of a foundation model; we show how RS3L pretraining enables powerful performance in downstream tasks such as discrimination of a variety of objects and uncertainty mitigation. In addition to our results, we make the RS3L dataset publicly available for further studies on how to improve SSL strategies.

We generalize the recently discovered planar decomposition (Kauffman bracket) for the Hoste-Ocneanu-Millett-Freyd-Lickorish-Yetter (HOMFLY) polynomials of bipartite knot/link diagrams to (anti)symmetrically colored HOMFLY polynomials. Cabling destroys planarity, but it is restored after projection to (anti)symmetric representations. This allows one to go beyond arborescent-induced calculus, which so far produced the majority of results for colored polynomials. Technicalities include combinations of projectors, and these can be handled rigorously, without any guess work—what can be also useful for other considerations, where reliable quantization was so far unavailable. We explicitly provide simple examples of calculation of the HOMFLY polynomials in symmetric representations with the use of our planar technique. These examples reveal what we call the bipartite evolution and the bipartite decomposition of squares of $\mathcal{R}$ matrix eigenvalues in the antiparallel channel.

We consider a scalar field coupled to the torsion in teleparallel gravity with a coupling function that does not allow for a tachyonic instability to occur, and it leads to the formation of new black holes with scalar hair. The scalarized black hole solutions are asymptotically flat, and they are studied under their thermodynamics, and we show that they are metastable solutions without phase transitions of first and second order. Also, we demonstrate the existence of distinct branches of solutions classified by the number of nodes of the scalar field. For the branches analyzed, the scalarized solutions have lower free energy than the Schwarzschild black hole; therefore, they are always thermodynamically preferred. Also, we show that the scalarized black holes are entropically favored compared to the Schwarzschild solution.

The possible existence of axions in the Universe introduces the intriguing possibility of photon-axion conversion in strong magnetic fields, particularly near compact objects like supermassive black holes or even naked singularity. In this study, we investigate the conversion of photons into axions in the vicinity of a Janis-Newman-Winicour (JNW) spacetime, a well-known naked singularity solution. We calculate the conversion probability and find that it is significantly influenced by the characteristic parameter of the JNW spacetime. The potential observational signatures of this conversion would be the dimming of photon ring in the x-ray and gamma-ray spectrum. Our findings suggest that compact objects like M87* could be prime candidates for detecting photon-axion conversion effects, provided future advances in high-resolution observations. Our analysis also suggests that the scattering of photons during the propagation through plasma is insignificant for the estimation of the conversion probability.

Oscillating clouds of ultralight bosons can grow around spinning black holes through superradiance, extracting energy and angular momentum, and eventually dissipating through gravitational radiation. Gravitational wave detectors like LIGO, Virgo, KAGRA, and LISA can thus probe the existence of ultralight bosons. In this study, we use fully general-relativistic solutions of the black hole-boson cloud systems to study the self-gravity effects of scalar and vector boson clouds, making only the simplifying assumption that the spacetime is axisymmetric (essentially corresponding to taking an oscillation average). We calculate the self-gravity shift in the cloud oscillation frequency, which determines the frequency evolution of the gravitational wave signal, finding that this effect can be up to twice as large in the relativistic regime compared to nonrelativistic estimates. We use this to improve the superrad waveform model, and estimate that this reduces the theoretical phase error to a few cycles over the characteristic timescale of the gravitational wave emission timescale for the louder vector boson signals. We also perform an analysis of the spacetime geometry of these systems, calculating how the cloud changes the innermost stable circular orbit and light ring around the black hole.

In light of the recent advances in lunar space missions, a great interest into using the Moon as a future environment for gravitational waves (GWs) detectors has been initiated. The Moon offers a unique environment for such detectors due to constrained noise sources, since unlike Earth it does not have oceans and atmosphere. In this paper, we further explore the idea of using the Moon as a giant resonator of GWs, a proposal that was first introduced by Weber in 1969. This idea is relaying on the theory how GWs interact with free masses and finally elastic solids, such as is a planet to some approximation. We start by carefully setting up general relativity (physics) and elastic theory (geophysics) background to be able to derive analytically the coupling between GWs and elastic solids through associated equations of motion. Once the analytical solution is derived, we explore the parameter space this interaction depends on. This eventually provides us with the transfer function, which defines the frequency band of the interest. We show how this interaction robustly depends on the regolith structure by altering the initial lunar model and exploring different regolith models. Our results show that detection might be troublesome in the high frequency regime between 0.1 and 1 Hz, without beforehand constraining the regolith structure with geophysical methods. Finally, we discuss what are the implications of detecting these signals with the future GW detectors build on the Moon.

Using the Einstein cluster models, we construct a fully relativistic, spherically symmetric, spiky structure of matter distribution near a supermassive black hole. We introduce and discuss three simple toy models, together with a more realistic model, which includes a Hernquist-type distribution with a typical galaxy scale. We find that the innermost stable circular orbit (ISCO) depends on the details of the environment and lies between the photon radius (at $3M_{\mathrm{BH}}$) and the ISCO radius of an isolated black hole of mass $M_{\mathrm{BH}}$ (at $6M_{\mathrm{BH}}$).

We analyze solutions of Chamseddine’s topological gravity in four-dimensional spacetime and discover various black hole solutions, with and without torsion, as well as solutions that describe naked singularities. Since all the solutions belong to the sector with vanishing scalar fields, they share the peculiar trait that all conserved charges are zero.

Primordial black holes (PBHs) in the mass range ${10}^{-16}-{10}^{-11}{M}_{\odot }$ may constitute all the dark matter. We show that gravitational microlensing of bright x-ray pulsars provide the most robust and immediately implementable opportunity to uncover PBH dark matter in this mass window. As proof of concept, we show that the currently operational NICER telescope can probe this window near ${10}^{-14}{M}_{\odot }$ with just two months of exposure on the x-ray pulsar SMC-X1, and that the forthcoming STROBE-X telescope can probe complementary regions in only a few weeks. These times are comparable to the week-long exposures obtained by NICER on various individual sources. We take into account the effects of wave optics and the finite extent of the source, which become important for the mass range of our PBHs. We also provide a spectral diagnostic to distinguish microlensing from transient background events and to broadly mark the PBH mass if true microlensing events are observed. In light of the powerful science case, i.e., the imminent discovery of dark matter searchable over multiple decades of PBH masses with achievable exposures, we strongly urge the commission of a dedicated large broadband telescope for x-ray microlensing. We derive the microlensing reach of such a telescope by assuming sensitivities of detector components of proposed missions and find that with hard x-ray pulsar sources PBH masses down to a few ${10}^{-17}{M}_{\odot }$ can be probed.

We analytically calculate one- and two-loop helicity amplitudes in massless QED, by adopting a four-dimensional tensor decomposition. We draw our attention to four-fermion and Compton scattering processes to higher orders in the dimensional regulator, as required for theoretical predictions at ${\mathrm{N}}^3\mathrm{LO}$. We organize loop amplitudes by proposing an efficient algorithm at integrand level to group Feynman graphs into integral families. We study the singular structure of these amplitudes and discuss the correspondence between QED and QCD processes. We present our results in terms of generalized polylogarithms up to transcendental weight six.

We calculate the leading-twist light cone distribution amplitudes of the $\mathrm{\Lambda }(uds)$ baryon using lattice QCD methods within the framework of large-momentum effective theory. Our numerical computations are carried out with $N_f=2+1$ stout smeared clover fermions and a Symanzik gauge action on a lattice with spacing $a=0.077\mathrm{fm}$ and a pion mass of 303 MeV. To approach the large-momentum region, we simulate the equal-time correlations with the hadron momentum $P^z=\{2.52,3.02,3.52\}\mathrm{GeV}$. We investigate the analytic properties of the baryon quasidistribution amplitude in coordinate space and validate them through our lattice calculations. After renormalization and extrapolation, we present results for the three-dimensional distribution in momentum fractions of the two light quarks. Based on these findings, we briefly discuss the phenomenological impact on weak decays of ${\mathrm{\Lambda }}_b$ and outline potential systematic uncertainties that can be improved in the future. This work lays the theoretical foundation for accessing baryon light cone distribution amplitudes from lattice QCD.

In this paper, we perform a complete calculation of the differential cross section for elastic neutrino-electron scattering at the one-loop level in the Standard Model (SM), by using up-to-date values of relevant input parameters in the on-shell renormalization scheme. A careful comparison with the calculation done by Sarantakos, Sirlin, and Marciano more than forty years ago in the same scheme is carried out, and an excellent agreement is found if the same values of input parameters are taken. Then we apply our results to compute the event rates for the detection of reactor antineutrinos in both JUNO and TAO experiments, which are now under construction and will soon be in operation. It should be emphasized that one-loop radiative corrections in the SM must be taken into account in the first place when searching for possible new-physics effects in the coming era of precision neutrino physics.

We find the dynamical tidal response of a Kerr black hole (BH) and demonstrate its tidal Love numbers to be nonvanishing when present in a nonaxisymmetric external tidal field. To leading order, they depend quadratically on the black hole spin and linearly on the mode frequency. This implies that Kerr BHs are deformable under certain external, time-dependent perturbations. Since nonvanishing tidal Love numbers have been used in compact binary coalescences observed by the LIGO-Virgo-KAGRA Collaboration to infer their non-BH nature, our findings have important implications on such inferences from future gravitational wave observations.