We report the results of a search for a light pseudoscalar particle $a$ that couples to electrons and decays to $e^{+}{e}^{-}$ performed using the high-energy CERN SPS H4 electron beam. If such light pseudoscalar exists, it could explain the ATOMKI anomaly (an excess of $e^{+}{e}^{-}$ pairs in the nuclear transitions of ${}^8\mathrm{Be}$ and ${}^4\mathrm{He}$ nuclei at the invariant mass $\simeq 17\mathrm{MeV}$ observed by the experiment at the 5 MV Van de Graaff accelerator at ATOMKI, Hungary). We used the NA64 data collected in the “visible mode” configuration with a total statistics corresponding to $8.4\times {10}^{10}$ electrons on target (EOT) in 2017 and 2018. In order to increase sensitivity to small coupling parameter $\epsilon$ we also used the data collected in 2016–2018 in the “invisible mode” configuration of NA64 with a total statistics corresponding to $2.84\times {10}^{11}$ EOT. The background and efficiency estimates for these two configurations were retained from our previous analyses searching for light vector bosons and axionlike particles (ALP) (the latter were assumed to couple predominantly to $\gamma$). In this work we recalculate the signal yields, which are different due to different cross section and lifetime of a pseudoscalar particle $a$, and perform a new statistical analysis. As a result, the region of the two dimensional parameter space $m_a-\epsilon$ in the mass range from 1 to 17.1 MeV is excluded. At the mass of the central value of the ATOMKI anomaly (the first result obtained on the beryllium nucleus, 16.7 MeV) the values of $\epsilon$ in the range $2.1\times {10}^{-4}<\epsilon <3.2\times {10}^{-4}$ are excluded.

We demonstrate that a Bjorken expanding strongly coupled $\mathcal{N}=4$ supersymmetric Yang-Mills plasma can display dynamically driven violations of the dominant and also the weak energy condition during hydrodynamization. In addition, we find that a period of vanishing entropy production in far-from-equilibrium stages induces later violations of the dominant energy condition in the strongly coupled plasma. Such violations cannot occur in a classical description of hydrodynamization and suggest that the inclusion of quantum effects in transport can lead to new phenomena in these regimes, even for systems without anomalies or spin.

We formulate the worldline approach of some field theories of fracton models and their symmetries. The distinction between the different models is based on their dispersion relations for the energy. In order to study the subsystem symmetries, we construct the Routhian functionals associated with the particle Lagrangians considered. We also build the pseudoclassical description of spinning fractons.

In this work we aim to investigate thick tori configurations around Kerr black holes with scalar hair (KBHsSH). For that goal, we provide a first approach using constant specific angular momentum non-self-gravitating Polish doughnuts. Through a series of examples, we show the feasibility of new topologies, such as double-centered tori with two cusps as well as similar structures as the ones found for rotating boson stars (BSs), namely, tori endowed with two centers and a single cusp. These KBHsSH solutions are also shown to possibly house static surfaces, associated with the static rings present in these spacetimes. Through this paper we highlight the differences between these fluid configurations when housed by some KBHsSH examples, standard Kerr black holes and rotating BSs.

Applying the perturbative approach to geodesic equations, we study motion of the test particles in time-dependent spherically symmetric spacetimes created by oscillating dark matter. Assuming the weakness of the gravitational field, we derive general formulas that describe infinite trajectories of the test particles and determine the total deflection angle in the leading order approximation. The obtained formulas are valid for both time-dependent and static matter configurations. Using these results, we calculate the deflection angle of a test particle passing through a spherically symmetric oscillating distribution of a self-gravitating scalar field with a logarithmic potential. It turns out that, in a wide range of amplitudes, oscillations in the deflection angle are sinusoidal and become small for ultrarelativistic particles.

It is well known that a black hole can be endowed with a topological charge coming as a result of phase transition(s) in the early universe. It has also recently been revealed that such an object might exist in one of the modified theory of gravity called the Eddington-inspired-Born-Infeld (EiBI) theory. Here we shall investigate the possibility of phase transitions, and in general thermodynamic phenomena, of EiBI-anti-de Sitter (AdS) black hole with (topologically-charged) global monopole. This is the first work that applies the full Euclidean action formalism in this model. We provide a counterterm to cancel infinities and argue that it is the most suitable among other possibilities. Our investigation reveals that the state variables obtained are found to obey the first law of black hole mechanics and Smarr’s law for black holes with $\mathrm{\Lambda }\ne 0$. Related to the second feature, we obtained the forbidden range of parameter space for EiBI AdS black hole with global monopole, which corresponds to $\frac{-(1-\mathrm{\Delta })}{\mathrm{\Lambda }}\le \kappa \le -\frac{1}{\mathrm{\Lambda }}$. The dependencies on $\mathrm{\Lambda }$, the EiBI constant $\kappa$ and the global monopole charge $\eta$ of the state variables and state functions obtained manifests in a Schwarzchild AdS-like phase transition for black holes with parameters below the lower bound of the forbidden range, and could also manifest in a Schwarzschild-flat like phase behavior for black holes with parameters above the higher bound of the forbidden range.

The amplitude of the primordial magnetic field (PMF) is constrained from observational limits on primordial nuclear abundances. Within this constraint, it is possible that nuclear motion is regulated by Coulomb scattering with electrons and positrons $(e^{\pm }\mathrm{s})$, while $e^{\pm }\mathrm{s}$ are affected by a PMF rather than collisions. For example, at a temperature of ${10}^9\mathrm{K}$, thermal nuclei typically experience $\sim {10}^{21}$ scatterings per second that are dominated by very small angle scattering leading to minuscule changes in the nuclear kinetic energy of order $\mathcal{O}(1)\mathrm{eV}$. In this paper the upper limit on the effects of a possible discretization of the $e^{\pm }$ momenta by the PMF on the nuclear momentum distribution is estimated under the extreme assumptions that the momentum of the $e^{\pm }$ is relaxed before and after Coulomb scattering to Landau levels, and that during Coulomb scattering the PMF is neglected. This assumption explicitly breaks the time reversal invariance of Coulomb scattering, and the Maxwell-Boltzmann distribution is not a trivial steady state solution of the Boltzmann equation under these assumptions. We numerically evaluate the collision terms in the Boltzmann equation, and show that the introduction of a special direction in the $e^{\pm }$ distribution by the PMF generates no directional dependence of the collisional destruction term of nuclei. Large anisotropies in the nuclear distribution function are then constrained from big bang nucleosynthesis. Ultimately, we conclude that a PMF does not significantly affect the isotropy or big bang nucleosynthesis.

The “$S_8$ tension” is a long-standing discrepancy between the cosmic microwave background (CMB) and weak gravitational lensing determination of the amplitude of matter fluctuations, parametrized as $S_8\equiv {\sigma }_8({\mathrm{\Omega }}_m/0.3{)}^{0.5}$, where ${\sigma }_8$ is the root-mean-square of matter fluctuations on an $8h^{-1}\mathrm{Mpc}$ scale, and ${\mathrm{\Omega }}_m$ is the total matter abundance. It was recently shown that dark matter (DM) decaying into a massless (dark radiation) and a massive (warm DM) species, with a lifetime ${\mathrm{\Gamma }}^{-1}\simeq 55(ϵ/0.007{)}^{1.4}\mathrm{Gyr}$—where $ϵ$ represent the mass-energy fraction transferred to the massless component—can ease the tension. Thanks to a fast and accurate fluid approximation scheme for the warm species, we perform a comprehensive study of this two-body decaying DM scenario, discussing in detail its dynamics and its impact on the CMB and linear matter power spectra. We then investigate the implications for the $S_8$ tension against a number of changes in the analysis: different $S_8$ priors, marginalization over the lensing information in Planck data, trading Planck high-$\ell$ polarization data for those from the SPTpol and ACTPol surveys, and the inclusion of the recent results from the Xenon1T Collaboration. We conclude that the preference for decaying DM, apparent only when the $S_8$ value determined from weak lensing data is added to the analysis, does not sensibly degrade the fit to any of the cosmological datasets considered, and that the model could potentially explain the anomalous electron recoil excess reported by the Xenon1T Collaboration. Furthermore, we explictly show that while current CMB data alone are not sensitive enough to distinguish between standard cold DM and decaying DM, next-generation CMB observations (CMB-S4) can unambiguously detect its signature.

We consider the general three-Higgs-doublet model (3HDM) and identify all limits that lead to exact Standard Model (SM) alignment. After discussing the underlying symmetries that can naturally enforce such an alignment, we focus on the most economic setting, called here the maximally symmetric three-Higgs-doublet model (MS-3HDM). The potential of the MS-3HDM obeys an Sp(6) symmetry, softly broken by bilinear masses and explicitly by hypercharge and Yukawa couplings through renormalization-group effects, whilst the theory allows for quartic coupling unification up to the Planck scale. Besides the two ratios of vacuum expectation values, $\tan {\beta }_{1,2}$, the MS-3HDM is predominantly governed by only three input parameters; the masses of the two charged Higgs bosons, $M_{h_{1,2}^{\pm }}$, and their mixing angle $\sigma$. Most remarkably, with these input parameters, we obtain definite predictions for the entire scalar mass spectrum of the theory, as well as for the SM-like Higgs-boson couplings to the gauge bosons and fermions. The predicted deviations of these couplings from their SM values might be probed at future precision high-energy colliders. The new phenomenological aspects of the MS-3HDM with respect to the earlier studied maximally symmetric two-Higgs-doublet model are discussed.

Algorithms based on normalizing flows are emerging as promising machine learning approaches to sampling complicated probability distributions in a way that can be made asymptotically exact. In the context of lattice field theory, proof-of-principle studies have demonstrated the effectiveness of this approach for scalar theories, gauge theories, and statistical systems. This work develops approaches that enable flow-based sampling of theories with dynamical fermions, which is necessary for the technique to be applied to lattice field theory studies of the Standard Model of particle physics and many condensed matter systems. As a practical demonstration, these methods are applied to the sampling of field configurations for a two-dimensional theory of massless staggered fermions coupled to a scalar field via a Yukawa interaction.

We investigate the IR phases of nonsupersymmetric (non-SUSY) $SO(N_c)$ gauge theories with $N_F$ fermions in the vector representation obtained by perturbing the SUSY theory with anomaly mediated SUSY breaking (AMSB). We find that of the wide variety of phases appearing in the SUSY theory only two survive: for $N_F\le \frac{3}{2}(N_c-2)$ the theory confines, breaking the $SU(N_F)$ global symmetry to $SO(N_F)$, while for $\frac{3}{2}(N_c-2)<N_F<3(N_c-2)$ the theory flows to a (super)conformal fixed point. The Abelian Coulomb and free magnetic phases do not survive and collapse to the confining phase. We also investigate the behavior of loop operators in order to provide a clear distinction between the confining and screened phases. With the choice of $\mathrm{Spin}(N_c)$ for the global structure of the gauge group, we find that the electric Wilson loop indeed obeys an area law, providing one of the first demonstrations of true confinement with chiral symmetry breaking in a non-SUSY theory. We identify monopole condensation as the dynamics underlying confinement. These monopoles arise naturally for $N_F=N_c-2$. The case with a smaller number of flavors can be obtained by integrating out flavors, and we confirm numerically that the monopole condensate persists in the presence of AMSB and mass perturbations.

Using next-to-leading order perturbative QCD, we calculate the diffractive contribution to inclusive dijet photoproduction in Pb-Pb ultraperipheral collisions (UPCs) at the LHC and find that it does not exceed 5–10% in small-$x_A$ bins in the ATLAS kinematics at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. Its smallness is a result of the restricted kinematics ($p_{T1}>20\mathrm{GeV}$ and $x_A>0.001$), the large nuclear suppression of nuclear diffractive parton distribution functions predicted in the leading twist model of nuclear shadowing, and additional suppression due to QCD factorization breaking in diffraction. At the same time, using looser $p_T$ cuts, e.g., $p_{T1}>10\mathrm{GeV}$ and $p_{Ti\ne 1}>5–7\mathrm{GeV}$, we find that $(d{\sigma }_{\mathrm{diff}}/d{x}_A)/(d{\sigma }_{\mathrm{inc}}/d{x}_A)$ can reach 10–20% at $x\approx 5\times {10}^{-4}$. Also, applying our framework to proton-proton UPCs at $\sqrt{s_{NN}}=13\mathrm{TeV}$, we find that the ratio of the diffractive and inclusive cross sections of dijet photoproduction $(d{\sigma }_{\mathrm{diff}}/d{x}_p)/(d{\sigma }_{\mathrm{inc}}/d{x}_p)$ is as large as 10–15% for $x_p\sim 5\times {10}^{-4}$. An account of the contribution of Pomeron-Pomeron scattering, which is not included in our analysis, should make this ratio somewhat larger.

We apply a dynamical three-constituent quark light-front model to study the proton. The dynamics is based on the notion of a diquark (bound or virtual) as the dominant interaction channel, which parameterize a contact interaction between the quarks in order to build the three-body Faddeev Bethe-Salpeter equations for the valence state, and we focus on the totally symmetric part of the wave function. The Dirac electromagnetic form factor is used to fix the model parameters, and the valence wave function is obtained. From that we investigate its Ioffe-time image, nonpolarized longitudinal and transverse momentum distributions, and the double momentum distribution.

We report the first observation of the processes $e^{+}{e}^{-}\to \mathrm{\Upsilon }(1\mathrm{S},2\mathrm{S})\eta$ at $\sqrt{s}=10.866\mathrm{GeV}$, with significance exceeding $10\sigma$ for both processes. The measured Born cross sections are $\sigma (e^{+}{e}^{-}\to \mathrm{\Upsilon }(2\mathrm{S})\eta )=2.07\pm 0.21\pm 0.19\mathrm{pb}$, and $\sigma (e^{+}{e}^{-}\to \mathrm{\Upsilon }(1\mathrm{S})\eta )=0.42\pm 0.08\pm 0.04\mathrm{pb}$. We also set the upper limit on the cross section of the process $e^{+}{e}^{-}\to \mathrm{\Upsilon }(1\mathrm{S}){\eta }^{\prime }$ to be $\sigma (e^{+}{e}^{-}\to \mathrm{\Upsilon }(1\mathrm{S}){\eta }^{\prime })<0.037\mathrm{pb}$ at 90% C.L. The results are obtained with the data sample collected with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider in the energy range from 10.63 to 11.02 GeV.

The violation of the Bell inequality for Dirac fermions is investigated in the cosmological de Sitter spacetime, in the presence of background electromagnetic fields of constant strengths. The orthonormal Dirac mode functions are obtained and the relevant in-out squeezed state expansion in terms of the Bogoliubov coefficients are found. We focus on two scenarios here: strong electric field and heavy mass limits (with respect to the Hubble constant). Using the squeezed state expansion, we then demonstrate the Bell violations for the vacuum and some maximally entangled initial states. Even though a background magnetic field alone cannot create particles, in the presence of background electric field and or spacetime curvature, it can affect the particle creation rate. Thus, our chief aim here is to investigate the role of the background magnetic field strength in the Bell violation. Qualitative differences in this regard for different maximally entangled initial states are shown. Further extension of these results to the so-called $\alpha$ vacua are also discussed.

We revisit evaluation of the chiral vortical effect in accelerated matter. To first order in the acceleration the corresponding matrix element of the axial current can be reconstructed from its flat-space limit. A crucial point is existence of an extra conservation law of fluid helicity which is not related to the symmetry of the Lagrangian. As a result, one can reproduce, via the equivalence principle, the effect of the so-called gravimagnetic anomaly; resolving in this way a long standing puzzle of its interpretation. Moreover, as a consequence of the extra conservation law the microscopic axial charge and helicity of the macroscopic motion are separately conserved. Some further consequences from the matching of the equivalence principle with hydrodynamics concerning higher orders in gradient expansion or in the acceleration are briefly discussed.

We study the linear perturbations about nonrotating black holes in the context of degenerate higher-order scalar-tensor (DHOST) theories, using a systematic approach that extracts the asymptotic behavior of perturbations (at spatial infinity and near the horizon) directly from the first-order radial differential system governing these perturbations. For axial (odd-parity) modes, this provides an alternative to the traditional approach based on a second-order Schrödinger-like equation with an effective potential, which we also discuss for completeness. For polar (even-parity) modes, which contain an additional degree of freedom in DHOST theories, and are thus more complex, we use a direct treatment of the four-dimensional first-order differential system (without resorting to a second order reformulation). We illustrate our study with two specific types of black hole solutions: “stealth” Schwarzschild black holes, with a nontrivial scalar hair, as well as a class of nonstealth black holes whose metric is distinct from Schwarzschild. The knowledge of the asymptotic behaviors of the perturbations enables us to compute numerically quasinormal modes, as we show explicitly for the nonstealth solutions. Finally, the asymptotic form of the modes also signals some pathologies in the stealth and nonstealth solutions considered here.

The traditional approach to perturbations of nonrotating black holes in general relativity uses the reformulation of the equations of motion into a radial second-order Schrödinger-like equation, whose asymptotic solutions are elementary. Imposing specific boundary conditions at spatial infinity and near the horizon defines, in particular, the quasinormal modes of black holes. For more complicated equations of motion, as encountered for instance in modified gravity models with different background solutions and/or additional degrees of freedom, we present a new approach that analyses directly the first-order differential system in its original form and extracts the asymptotic behavior of perturbations, without resorting to a second-order reformulation. As a pedagogical illustration, we apply this treatment to the perturbations of Schwarzschild black holes and then show that the standard quasinormal modes can be obtained numerically by solving this first-order system with a spectral method. This new approach paves the way for a generic treatment of the asymptotic behavior of black hole perturbations and the identification of quasinormal modes in theories of modified gravity.

The current paper is dedicated to developing a ($3+1$) decomposition for the minimal gravitational Standard-Model Extension. Our setting is explicit diffeomorphism violation and we focus on the background fields known in the literature as $u$ and $s^{\mu \nu }$. The Hamiltonian formalism is developed for these contributions, which amounts to deriving modified Hamiltonian and momentum constraints. We then study the connection between these modified constraints and the modified Einstein equations. Implications are drawn on the form of the background fields to guarantee the internal consistency of the corresponding modified-gravity theories. In the course of our analysis, we obtain a set of consistency requirements for $u$ and certain sectors of $s^{\mu \nu }$. We argue that the constraint structure remains untouched when these conditions are satisfied. Our results shed light on explicit violations of diffeomorphism invariance and local Lorentz invariance in gravity. They may turn out to be valuable for developing a better understanding of effective modified-gravity theories.

The observation of the shadow of the supermassive black hole $\mathrm{M}{87}^{*}$ by the Event Horizon Telescope (EHT) is sensitive to the spacetime geometry near the circular photon orbit and beyond, and it thus has the potential to test general relativity in the strong field regime. Obstacles to this program, however, include degeneracies between putative deviations from general relativity and both the description of the accretion flow and the uncertainties on “calibration parameters,” such as, e.g., the mass and spin of the black hole. In this work, we introduce a formalism, based on a principal component analysis, capable of reconstructing the black hole metric (i.e., the “signal”) in an agnostic way, while subtracting the “foreground” due to the uncertainties in the calibration parameters and the modeling of the accretion flow. We apply our technique to simulated mock data for spherically symmetric black holes surrounded by a thick accretion disk. We show that separation of signal and foreground may be possible with next generation EHT-like experiments.