We have studied neutral and charged current (anti)neutrino induced $\eta$ production off the free nucleon target at MicroBooNE energies, in the light of recent results reported by the MicroBooNE collaboration for the total $\eta$ production cross section. This study has been made using a theoretical model in which the weak hadronic current receives contribution from the nonresonant Born terms as well as from the resonance excitations. The Born terms are obtained using the SU(3) symmetric chiral model, used earlier in the study of $K$—meson production. The contribution from the resonance terms is considered from the excitation of five nucleon resonances viz. $S_{11}(1535)$, $S_{11}(1650)$, $P_{11}(1710)$, $P_{11}(1880)$, and $S_{11}(1895)$. To fix the parameters of the vector current interaction, this model is first used to study the electromagnetic production of $\eta$ mesons induced by real and virtual photons, and the theoretical results have been compared with the data from the MAINZ and JLab experiments. The partially conserved axial-vector current hypothesis and generalized Goldberger-Treiman relation are used to fix the parameters of the axial-vector current interaction. The results are presented for the total cross section for the neutral and charged current induced $\eta$ production, ratio of the cross sections for the charged current to neutral current, MicroBooNE flux averaged cross section $⟨\sigma ⟩$, $⟨\frac{d\sigma }{d{Q}^2}⟩$, and $⟨\frac{d\sigma }{d{p}_{\eta }}⟩$, which may be useful in the future analysis of MicroBooNE as well as other accelerator and atmospheric neutrino experiments being performed in the $\mathcal{O}(1)\mathrm{GeV}$ energy region.

The cross sections of the $e^{+}{e}^{-}\to \varphi {\eta }^{\prime }$ process at center-of-mass energies from 3.508 to 4.951 GeV are measured with high precision using $26.1{\mathrm{fb}}^{-1}$ data collected with the BESIII detector operating at the BEPCII storage ring. The cross sections are of the order of a few picobarn and decrease as the center-of-mass energy increases as $s^{-n/2}$ with $n=4.35\pm 0.14$. This result is in agreement with the Nambu-Jona-Lasinio model prediction of $n=3.5\pm 0.9$. In addition, the charmless decay $\psi (3770)\to \varphi {\eta }^{\prime }$ is searched for by fitting the measured cross sections, yet no significant signal is observed. The upper limit of $\mathcal{B}(\psi (3770)\to \varphi {\eta }^{\prime })$ at the 90% confidence level is determined to be $2.3\times {10}^{-5}$.

Möbius-ring resonators stem from a well-studied and fascinating geometrical structure which features a one-sided topology, the Möbius strip, and have been shown to exhibit fermion rotational symmetry with respect to a ring resonator with no twist (which exhibits boson rotational symmetry) [Phys. Rev. Lett. 101, 247701 (2008)]. Here, we present a new type of resonator through the formation of twisted hollow structures using equilateral triangular cross sections, which leads to the realization of a cavity with anyon rotational symmetry. Unlike all previous cavity resonators, the anyon resonator permits the existence of bulk resonant modes that exhibit nonzero electromagnetic helicity in vacuo, with nonzero overlap of the electric and magnetic mode eigenvectors, $\int {\mathbf{E}}_p·{\mathbf{B}}_{p}d\tau$, integrated over the cavity volume. In the upconversion limit, we show that these nonzero helical modes couple naturally to ultralight dark matter axions within the bandwidth of the resonator by adding amplitude modulated sidebands through the axion-photon chiral anomaly. Thus, we show a sensitive ultralight dark matter experiment may be realized by implementing such a resonator in an ultrastable oscillator configuration and searching for signals in the Fourier spectrum of amplitude fluctuations. This removes the typical requirement for an external magnetic field and therefore permits the use of superconducting materials to reduce surface losses and enhance sensitivity to axions.

In this paper, we present experimental results and numerical simulations of trident production, $e^{-}\to e^{-}{e}^{+}{e}^{-}$, in a strong electromagnetic field. The experiment was conducted at CERN for the purpose of probing the strong-field parameter $\chi$ up to 2.4, using a 200 GeV electron beam penetrating a $400\mathrm{\mu }\mathrm{m}$ thick germanium crystal oriented along the $⟨110⟩$ axis. For the current experimental parameters we found that the trident process is primarily a two-step process, and show remarkable agreement between theoretical predictions and experimental data. This paper is an extension of the previously published paper [C. F. Nielsen et al., Phys. Rev. Lett. 130, 071601 (2023)] and features new analysis differential in the energy of the produced positron and electron in the trident process. Even for the more demanding differential analysis, we find good agreement between theoretical predictions and experimental data, while a slight discrepancy is found in the high energy tail of the trident spectrum. This discrepancy could be an indication of the direct process, but further investigation is needed due to the large uncertainties in this part of the spectrum. Finally we present a suggestion for a future experiment, aiming to probe the direct process using thin crystals.

We present differential double-copy relations between gluon and graviton three-point functions in ${\mathrm{AdS}}_{d+1}$. We introduce a set of differential operators in anti–de Sitter (AdS) that naturally generalize on shell kinematics of scattering amplitudes in flat space. This provides a way to construct AdS correlators by replacing the kinematic variables of amplitudes with the corresponding differential operators and suitably ordering them. By construction, the resulting correlators are manifestly conformally invariant, with the correct flat-space limit and exhibit a differential double-copy structure.

We study the interaction between gravitational waves and quantum matter such as Bose-Einstein condensates, superfluid helium, or ultracold solids, explicitly taking into account the changes of the trapping potential induced by the gravitational wave. As a possible observable, we consider the change of energy due to the gravitational wave, for which we derive rigorous bounds in terms of kinetic energy and particle number. Finally, we discuss implications for possible experimental tests.

Several rapid parameter estimation methods have recently been advanced to deal with the computational challenges of the problem of Bayesian inference of the properties of compact binary sources detected in the upcoming science runs of the terrestrial network of gravitational wave detectors. Some of these methods are well-optimized to reconstruct gravitational wave signals in nearly real-time necessary for multimessenger astronomy. In this context, this work presents a new, computationally efficient algorithm for fast evaluation of the likelihood function using a combination of numerical linear algebra and meshfree interpolation methods. The proposed method can rapidly evaluate the likelihood function at any arbitrary point of the sample space at a negligible loss of accuracy and is an alternative to the grid-based parameter estimation schemes. We obtain posterior samples over model parameters for a canonical binary neutron star system by interfacing our fast likelihood evaluation method with the nested sampling algorithm. The marginalized posterior distributions obtained from these samples are statistically identical to those obtained by brute force calculations. We find that such Bayesian posteriors can be determined within a few minutes of detecting such transient compact binary sources, thereby improving the chances of their prompt follow-up observations with telescopes at different wavelengths. It may be possible to apply the blueprint of the meshfree technique presented in this study to Bayesian inference problems in other domains.

In the gravitational theory containing the second-order interaction of gravity with the scalar and electromagnetic fields at most, the black hole entropy obeying the linearized second law of black hole thermodynamics has been obtained. To generally study the linearized second law of black hole thermodynamics, we extend the gravitational theory to include higher-order interactions of gravity with the scalar and electromagnetic fields. We derive the general expression of black hole entropy satisfying the linearized second law, which is expressed as the Wald entropy with correction terms. It is worth noting that the correction terms consist of both the minimal and nonminimal coupling interactions between gravity and the scalar field, and the contribution of the electromagnetic field is not involved. Since the black hole entropy satisfying the linearized second law is determined only by the nonminimum coupling interactions in gravity according to the previous perspective, this result upends our understanding of the linearized second law in general gravitational theory.

The radial direction of the Peccei-Quinn field can drive cosmic inflation, given a nonminimal coupling to gravity. This scenario has been considered to simultaneously explain inflation, the strong $CP$ problem, and dark matter. We argue that Peccei-Quinn inflation is extremely sensitive to higher-dimensional operators. Further combining with the discussion on the axion quality required for solving the strong $CP$ problem, we examine the validity of this scenario. We also show that after Peccei-Quinn inflation, resonant amplifications of the field fluctuation is inevitably triggered.

We study the evolution of magnetic fields coupled with chiral fermion asymmetry in the framework of chiral magnetohydrodynamics with zero initial total chirality. The initial magnetic field has a turbulent spectrum peaking at a certain characteristic scale and is fully helical with positive helicity. The initial chiral chemical potential is spatially uniform and negative. We consider two opposite cases where the ratio of the length scale of the chiral plasma instability (CPI) to the characteristic scale of the turbulence is smaller and larger than unity. These initial conditions might be realized in cosmological models, including certain types of axion inflation. The magnetic field and chiral chemical potential evolve with inverse cascading in such a way that the magnetic helicity and chirality cancel each other at all times, provided there is no spin flipping. The CPI timescale is found to determine mainly the time when the magnetic helicity spectrum attains negative values at high wave numbers. The turnover time of the energy-carrying eddies, on the other hand, determines the time when the peak of the spectrum starts to shift to smaller wave numbers via an inverse cascade. The onset of helicity decay is determined by the time when the chiral magnetic effect becomes efficient at the peak of the initial magnetic energy spectrum, provided the CPI does not grow much. When spin flipping is important, the chiral chemical potential vanishes at late times and the magnetic helicity becomes constant, which leads to a faster increase of the correlation length. This is in agreement with what is expected from magnetic helicity conservation and also happens when the initial total chirality is imbalanced. Our findings have important implications for baryogenesis after axion inflation.

We prove the conditions under which scaling cosmologies are inevitable late-time attractors of multifield multiexponential potentials, independently of initial conditions. The advantage of such scaling cosmologies is that the time dependence of the fields and of the scale factor is known analytically, thus allowing late-time observables to be determined exactly. Expanding our earlier results, here we continue the program of analytically characterizing the late-time behavior of cosmological solutions. Our results are general in that they are derived without relying on any approximation nor are they based on any assumption on the sources of the potential, such as their higher-dimensional or string-theoretic origin. We point out a number of model-independent features that follow from our analytic results, including a convex-hull criterion for cosmic acceleration. When applied to string theory, our analytic knowledge of late-time cosmological solutions enables us to single out potentials that can describe an accelerating universe from those which cannot and to quantitatively test several conjectured swampland criteria.

We investigate whether an accelerating universe can be realized as an asymptotic late-time solution of Friedmann–Lemaître–Robertson–Walker (FLRW)-cosmology with multifield multiexponential potentials. Late-time cosmological solutions exhibit a universal behavior which enables us to bound the rate of time variation of the Hubble parameter. In string-theoretic realizations, if the dilaton remains a rolling field, our bound singles out a tension in achieving asymptotic late-time cosmic acceleration. Our findings go beyond previous no-go theorems in that they apply to arbitrary multiexponential potentials and make no specific reference to vacuum or slow-roll solutions. We also show that if the late-time solution approaches a critical point of the dynamical system governing the cosmological evolution, the criterion for cosmic acceleration can be generally stated in terms of a directional derivative of the potential.

Spinning neutron stars (NSs) can emit continuous gravitational waves (GWs) that carry a wealth of information about the compact object. If such a signal is detected, it will provide us with new insight into the physical properties of matter under extreme conditions. According to binary population synthesis simulations, future space-based GW detectors, such as LISA and TianQin, can potentially detect some double NSs in tight binaries with orbital periods shorter than 10 minutes. The possibility of a successful directed search for continuous GWs from the spinning NS in such a binary system identified by LISA/TianQin will be significantly increased with the proposed next-generation ground-based GW observatories, such as Cosmic Explorer and Einstein Telescope. Searching for continuous GWs from such a tight binary system requires highly accurate waveform templates that account for the interaction of the NS with its companion. In this spirit, we derive analytic approximations that describe the GWs emitted by a triaxial nonaligned NS in a binary system in which the effects of spin-orbit coupling have been incorporated. The difference with the widely used waveform for the isolated NS is estimated and the parameter estimation accuracy of an example signal using Cosmic Explorer is calculated. For a typical tight double NS system with a 6 min orbital period, the angular frequency correction of the spinning NS in this binary due to spin precession is $\sim {10}^{-6}\mathrm{Hz}$, which is in the same order of magnitude as the angular frequency of orbital precession. The fitting factor between the waveforms with and without spin precession will drop to less than 0.97 after a few days ($\sim {10}^5\mathrm{s}$). We find that spin-orbit coupling has the potential to improve the accuracy of parameter estimation, especially for the binary inclination angle and spin precession cone opening angle, by up to 3 orders of magnitude.

A few systematizing remarks concerning a spherically symmetric approximation in the description of compact stars with gravitationally strong magnetic fields are given, including the problem of the definition of mass accounting for the electromagnetic mass contribution. The problem of effective magnetic charges associated with the approximation method is addressed. Two simple models of compact stars with ultrastrong magnetic fields of ${10}^{17}–{10}^{18}\mathrm{Gs}$ are studied in the limiting approximation of exact spherical symmetry, which is the limit of considered spherical approximations. Under this condition the characteristics of the magnetized MIT-bag strange quark star show scaling with the bag constant, which can be shown to be a result of a scaling symmetry of the equations of stellar structure. The model is compared with a neutron star model described by the $\mathrm{UV}14+\mathrm{TNI}$ equation of state. At the strongest fields, the masses of the modeled stars exceed values normally expected for compact stars and ascribed rather to black holes or models with exotic equations of state. Based on the considered neutron star example, it seems that too strong magnetic fields may render models of compact stars radially instable.

In certain classes of the scalar-Gauss-Bonnet theory strong spacetime curvature in the vicinity of neutron stars and black holes can spontaneously trigger scalarization in the compact object if the coupling strength of the scalar field to the Gauss-Bonnet invariant exceeds a critical value. Specifying on neutron stars, this threshold depends on the mass and equation of state. The presence of a companion will further influence the required coupling strength for scalarization, and thus, a stable hair can be installed at a lower magnitude of coupling for those neutron stars as members of binaries. Focusing on binary neutron star mergers, we investigate this latter dynamically driven scalarization, and find that the reduction in the threshold coupling strength seems to be more profound for symmetric binaries, while the threshold is only marginally reduced for rather asymmetric binaries. The associated scalar radiation is also discussed. We discover in addition a universal relation between the critical coupling strength and the stellar compactness for isolated neutron stars and perform a detailed comparison with the dynamical scalarization threshold. In synergy with such relations, one can, at least in principle, constrain the theory parameters regardless of the uncertainty in the equation of state.

We study the importance of the thermal behavior of the hadron-quark phase transition in neutron star (NS) mergers. To this end, we devise a new scheme approximating thermal effects to supplement cold, barotropic equation of state (EOS) models, which is particularly designed for hybrid EOSs, i.e. two-phase EOS constructions with a hadronic regime and a phase of deconfined quark matter. As in a previous, commonly adopted, approximate thermal treatment, we employ an ideal-gas component to model thermal pressure but, additionally, we include an improved description for the coexistence phase of hybrid EOSs. In contrast to the older scheme, our method considers the temperature dependence of the phase boundaries. This turns out to be critical for a quantitative description of quark matter effects in NS mergers, since the coexistence phase can introduce a strong softening of the EOS at finite temperature, which is even more significant than the change of the EOS by the phase transition at $T=0$. We validate our approach by comparing to existing fully temperature-dependent EOS models and find a very good quantitative agreement of postmerger gravitational-wave (GW) features as a figure of merit sensitively tracking the dynamics and thus the impact of quark matter in merger remnants. Simulations with the original thermal ideal-gas approach exhibit sizable differences compared to full hybrid models implying that its use in NS merger simulations with quark matter is problematic. Importantly, our new scheme provides the means to isolate thermal effects of quark matter from the properties of the cold hybrid EOS and thus allows an assessment of the thermal behavior alone. Generally, we find that the thermal properties in hybrid models are more important compared to the thermal behavior of purely baryonic matter. We show that different shapes of the phase boundaries at finite temperature can have a large impact on the postmerger dynamics and GW signal for the same cold hybrid model. This finding demonstrates that postmerger GW emission contains important complementary information compared to properties extracted from cold stars in isolation or during a binary inspiral. We also show by concrete examples that it is even possible for quark matter to only occur and thus be detectable in finite-temperature systems like merger remnants but not in cold NSs. All these findings also illustrate that heavy-ion collision experiments as a probe of the phase diagram at finite temperature bear relevant information for the astrophysics of NS mergers and core-collapse supernovae. Furthermore, our new thermal treatment features the flexibility to be combined with any cold, barotropic hybrid model including effective models of phase transitions, where a large number of models is available. This allows to conduct large parameter studies to comprehensively understand the effects of quark matter in NS mergers.

We investigate the effects of the momentum spread of photon around incoming electrons during nonlinear Compton scattering of an elliptically polarized laser off an ultrarelativistic electron beam. It has been assumed to be a good approximation to neglect the angular spread in the strong-field QED codes considering its smallness in relativistic regime. Here, we scrutinize the validity of this approximation in the nonlinear Compton scattering. For our purpose, we improved the fully electron spin- and photon polarization-resolved Monte Carlo simulation method by employing the angle-resolved probability for high-energy photon emission in ultrastrong laser fields. The quantum operator method introduced by Baier and Katkov is employed for calculation of the probability within the quasiclassical approach and the local constant field approximation. Our simulation shows that the angular spread at emission has notable effects on angular distribution and polarization of outgoing particles. The width of angular distributions for electrons and emitted photons are increased. Meanwhile, the electrons polarization is reduced due to the correction of radiation reaction force, while the average polarization of photons is insensitive to the angular spread at emissions.