Observations of neutron stars (NSs) by the LIGO-Virgo and NICER collaborations have provided reasonably precise measurements of their various macroscopic properties. In this paper, we employ a Bayesian framework to combine them and place improved joint constraints on the properties of the NS equation of state (EOS). We use a hybrid EOS formulation that employs a parabolic expansion-based nuclear empirical parametrization around the nuclear saturation density augmented by a generic 3-segment piecewise polytrope model at higher densities. Within the 90% credible level this parametrization predicts $R_{1.4}={12.57}_{-0.92}^{+0.73}\mathrm{km}$ and ${\mathrm{\Lambda }}_{1.4}={550}_{-225}^{+223}$ for the radius and dimensionless tidal deformability, respectively, of a $1.4M_{\odot }$ NS. Finally, we show how the construction of the full NS EOS based solely on the nuclear empirical parameters at saturation density leads to certain tension with the astrophysical data, and how the hybrid approach provides a resolution to it.

To investigate possible topological vortex structures in generalized models, we developed a perturbative generation approach for scalar-vector theories. We demonstrate explicitly that the dielectric permeability functions must have a nonpolynomial shape, i.e., the form of the logarithmic function. Based on this result, we built models in $(2+1)D$ with logarithmic dielectric permeability in order to investigate the presence of topological vortex structures in a Maxwell model. This type of scalar-vector models is important because it can generate stationary field solutions in theories describing the dynamics of the scalar field. As examples, we chose models of the complex scalar field coupled to the Maxwell field. Subsequently, we investigated the model’s Bogomol’nyi equations to describe the field configurations. Then, we demonstrate numerically, for an ansatz with rotational symmetry, that the solutions of the complex scalar field generating minimum energy configurations are topological structures depending on the parameters obtained in the perturbative generation of the vector-scalar theory.

Light-front wave functions motivated by holographic constructions are used to study Bloom-Gilman duality, a feature of deep inelastic scattering. Separate expressions for structure functions in terms of quark and hadronic degrees of freedom (involving transition form factors) are presented, with an ultimate goal of obtaining a relationship between the two expressions. A specific two-parton model is defined and resonance transition form factors are computed using previously derived light-front wave functions. A new form of global duality (integral over all values of $x$ between 0 and 1) is derived from the valence quark-number sum rule. Using a complete set of hadronic states is necessary for this new global duality to be achieved, and the previous original work does not provide such a set. This feature is remedied by amending the model to include a longitudinal confining potential, and the resulting complete set is sufficient to carry out the study of Bloom-Gilman duality. Specific expressions for transition form factors are obtained and all are shown to fall as $1/Q^2$, at asymptotically large values. This is because the Feynman mechanism dominates the asymptotic behavior of the model. These transition form factors are used to assess the validity of the global and local duality sum rules, with the result that both are not satisfied within the given model. Evaluations of the hadronic expression for $q(x,Q^2)$ provide more details about this lack. This result is not a failure of the current model because it shows that the observed validity of both global and local forms of duality for deep inelastic scattering must be related to a feature of QCD that is deeper than completeness. Our simple present model suggests a prediction that Bloom-Gilman duality would not be observed if deep inelastic scattering experiments were to be made on the pion. The underlying origin of the duality phenomenon in deep inelastic scattering is deeply buried within the confinement aspects of QCD, and its origin remains a mystery.

In this paper, we solve the new evolution equation for high energy scattering amplitude that stems from the Gribov-Zwanziger approach to the confinement of quarks and gluons. We found that (1) the energy dependence of the scattering amplitude turns out to be the same as for QCD Balitsky, Fadin, Kuraev and Lipatov (BFKL) evolution, (2) the spectrum of the new equation does not depend on the details of the Gribov-Zwanzinger approach, and (3) all eigenfunctions coincide with the eigenfunctions of the QCD BFKL equation at large transverse momenta $\kappa \ge 1$. The numerical calculations show that there exist no new eigenvalues with the eigenfunctions which decrease faster than solutions of the QCD BFKL equation at large transverse momenta. The structure of the gluon propagator in the Gribov-Zwanziger approach, that stems from the lattice QCD and from the theoretical evaluation, results in the exponential suppression of the eigenfunctions at long distances and in the resolution of the difficulties, which the color glass condensate and some other approaches, based on perturbative QCD, face at large impact parameters. We can conclude that the confinement of quark and gluons, at least in the form of the Gribov-Zwanziger approach, does not influence on the scattering amplitude except for solving the long-standing theoretical problem of its behavior at large impact parameters.

We analyze the results recently presented on the $B^{+}\to K^{*+}{\mu }^{+}{\mu }^{-}$ angular observables by the LHCb Collaboration, which show indications for new physics beyond the Standard Model. Within a model-independent analysis, we compare the fit results with the corresponding results for the angular observables in $B^0\to K^{*0}{\mu }^{+}{\mu }^{-}$.

Black hole superradiance is a powerful probe of light, weakly coupled hidden sector particles. Many candidate particles, such as axions, generically have self-interactions that can influence the evolution of the superradiant instability. As pointed out in [A. Gruzinov, arXiv:1604.06422.] in the context of a toy model, much of the existing literature on spin-0 superradiance does not take into account the most important self-interaction-induced processes. These processes lead to energy exchange between quasi-bound levels and particle emission to infinity; for large self-couplings, superradiant growth is saturated at a quasi-equilibrium configuration of reduced level occupation numbers. In this paper, we perform a detailed analysis of the rich dynamics of spin-0 superradiance with self-interactions, and the resulting observational signatures. We focus on quartic self-interactions, which dominate the evolution for most models of interest. We explore multiple distinct regimes of parameter space introduced by a nonzero self-interaction, including the simultaneous population of two or more bound levels; at large coupling, we confirm the basic picture of quasiequilibrium saturation and provide evidence that the “bosenova” collapse does not occur in most of the astrophysical parameter space. Compared to gravitational superradiance, we find that gravitational wave “annihilation” signals and black hole spin-down are parametrically suppressed with increasing interactions, while new gravitational wave “transition” signals can take place for moderate interactions. The novel phenomenon of scalar wave emission is less suppressed at large couplings, and if the particle has Standard Model interactions, then coherent, monochromatic axion wave signals from black hole superradiance may be detectable in proposed axion dark matter experiments.

We propose a self-interacting inelastic dark matter (DM) scenario as a possible origin of the recently reported excess of electron recoil events by the XENON1T experiment. Two quasidegenerate Majorana fermion DM particles interact within themselves via a light hidden sector massive gauge boson and with the standard model particles via gauge kinetic mixing. We also consider an additional long-lived singlet scalar, which helps in realizing correct dark matter relic abundance via a hybrid setup comprising both freeze-in and freeze-out mechanisms. While being consistent with the required DM phenomenology along with sufficient self-interactions to address the small-scale issues of cold dark matter, the model with GeV-scale DM can explain the XENON1T excess via inelastic down-scattering of the heavier DM component into the lighter one. All these requirements leave a very tiny parameter space, keeping the model very predictive for near-future experiments.

We present the nonperturbative computation of renormalization factors in the ${\mathrm{RI}}^{\prime }\text{−}(\mathrm{S})\mathrm{MOM}$ (regularization independent (symmetric) momentum subtraction) schemes for the QCD gauge field ensembles generated by the CLS (coordinated lattice simulations) effort with three flavors of nonperturbatively improved Wilson (clover) quarks. We use ensembles with the standard (anti-)periodic boundary conditions in the time direction as well as gauge field configurations with open boundary conditions. Besides flavor-nonsinglet quark-antiquark operators with up to two derivatives we also consider three-quark operators with up to one derivative. For the ${\mathrm{RI}}^{\prime }\text{−}\mathrm{SMOM}$ scheme results we make use of the recently calculated three-loop conversion factors to the $\overline{\mathrm{MS}}$ scheme.

Using the dynamical diquark model, we calculate the electric-dipole radiative decay widths to $X(3872)$ of the lightest negative-parity exotic candidates, including the four $I=0$, $J^{PC}=1^{--}$ (“$Y$”) states. The $O(100–1000\mathrm{keV})$ values obtained test the hypothesis of a common substructure shared by all of these states. We also calculate the magnetic-dipole radiative decay width for $Z_c(4020{)}^0\to \gamma X(3872)$, and find it to be rather smaller ($<10\mathrm{keV}$) than its predicted value in molecular models.

The rare decay ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}{e}^{+}{e}^{-}$ is studied using a sample of $1.3\times {10}^{9}J/\psi$ events collected with the BESIII detector at BEPCII in 2009 and 2012. The branching fraction is measured with improved precision to be $(2.42\pm 0.05_{\mathrm{stat}}\pm 0.08_{\mathrm{syst}})\times {10}^{-3}$. Due to the inclusion of new data, this result supersedes the last BESIII result on this branching fraction. In addition, the $CP$-violating asymmetry in the angle between the decay planes of the ${\pi }^{+}{\pi }^{-}$-pair and the $e^{+}{e}^{-}$-pair is investigated. A measurable value would indicate physics beyond the standard model; the result is ${\mathcal{A}}_{CP}=(2.9\pm 3.7_{\mathrm{stat}}\pm 1.1_{\mathrm{syst}})\%$, which is consistent with the standard model expectation of no $CP$-violation. The precision is comparable to the asymmetry measurement in the $K_L^0\to {\pi }^{+}{\pi }^{-}{e}^{+}{e}^{-}$ decay where the observed $(14\pm 2)\%$ effect is driven by a standard model mechanism.

Using $6.32{\mathrm{fb}}^{-1}$ of electron-positron collision data recorded by the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV, we present the first search for the decay $D_s^{+}\to a_0(980{)}^0{e}^{+}{\nu }_e$, $a_0(980{)}^0\to {\pi }^0\eta$, which could proceed via $a_0(980)-f_0(980)$ mixing. No significant signal is observed. An upper limit of $1.2\times {10}^{-4}$ at the 90% confidence level is set on the product of the branching fractions of $D_s^{+}\to a_0(980{)}^0{e}^{+}{\nu }_e$ and $a_0(980{)}^0\to {\pi }^0\eta$ decays.

The spectrum of bound states of special strongly coupled confining field theories might include a parametrically light dilaton, associated with the formation of enhanced condensates that break (approximate) scale invariance spontaneously. It has been suggested in the literature that such a state may arise in connection with the theory being close to the unitarity bound in holographic models. We extend these ideas to cases where the background geometry is non-anti-de Sitter, and the gravity description of the dual confining field theory has a top-down origin in supergravity. We exemplify this program by studying the circle compactification of Romans six-dimensional half-maximal supergravity. We uncover a rich space of solutions, many of which were previously unknown in the literature. We compute the bosonic spectrum of excitations and identify a tachyonic instability in a region of parameter space for a class of regular background solutions. A tachyon only exists along an energetically disfavored (unphysical) branch of solutions of the gravity theory; we find evidence of a first-order phase transition that separates this region of parameter space from the physical one. Along the physical branch of regular solutions, one of the lightest scalar particles is approximately a dilaton, and it is associated with a condensate in the underlying theory. Yet, because of the location of the phase transition, its mass is not parametrically small, and it is, coincidentally, the next-to-lightest scalar bound state, rather than the lightest one.

We discuss, on general grounds, how two subgraphs of a given Feynman graph can overlap with each other. For this, we use the notion of connecting and returning lines that describe how any subgraph is inserted within the original graph. This, in turn, allows us to derive “nonoverlap” theorems for one-particle-irreducible subgraphs with 2, 3 and 4 external legs. As an application, we provide a simple justification of the skeleton expansion for vertex functions with more than five legs, in the case of scalar field theories. We also discuss how the skeleton expansion can be extended to other classes of graphs.

We derive a manifestly duality-symmetric formulation of the action principle for conformal gravity linearized around Minkowski space-time. The analysis is performed in the Hamiltonian formulation, the fourth-order character of the equations of motion requiring the formal treatment of the three-dimensional metric perturbation and the extrinsic curvature as independent dynamical variables. The constraints are solved in terms of two symmetric potentials that are interpreted as a dual three-dimensional metric and a dual extrinsic curvature. The action principle can be written in terms of these four dynamical variables, duality acting as simultaneous rotations in the respective spaces spanned by the three-dimensional metrics and the extrinsic curvatures. A twisted self-duality formulation of the equations of motion is also provided.

Extending the background metric optimization procedure for Euclidean path integrals of two-dimensional conformal field theories, introduced by Caputa et al. [Phys. Rev. Lett. 119, 071602 (2017), J. High Energy Phys. 11 (2017) 097], to a $z=2$ anisotropically scale-invariant $(2+1)$-dimensional Lifshitz field theory of a free massless scalar field, we find optimal geometries for static and dynamic correlation functions. For the static correlation functions, the optimal background metric is equivalent to an AdS metric on a Poincaré patch, while for dynamical correlation functions, we find Lifshitz like metric. This results suggest that a MERA-like tensor network, perhaps without unitarity, would still be considered an optimal background spacetime configuration for the numerical description of this system, even though the classical action we start with is not a conformal field theory.

We study photon orbits in the background of ($1+3$)-dimensional static, spherically symmetric geometries. In particular, we have obtained exact analytical solutions to the null geodesic equations for light rays in terms of the Weierstraß function for space-times arising in the context of scale-dependent gravity. The trajectories in the ($x-y$) plane are shown graphically, and we make a comparison with similar geometries arising in different contexts. The light deflection angle is computed as a function of the running parameter $\xi$, and an upper bound for the latter is obtained.

Two exact lens equations have been recently shown to be equivalent to each other, being consistent with the gravitational deflection angle of light from a source to an observer, both of which can be within a finite distance from a lens object [Phys. Rev. D 102, 064060 (2020)]. We examine methods for iterative solutions of the gravitational lens equations in the strong deflection limit. It has been so far unclear whether a convergent series expansion can be provided by the gravitational lens approach based on the geometrical optics for obtaining approximate solutions in the strong deflection limit in terms of a small offset angle. By using the ratio of the lens mass to the lens distance, we discuss a slightly different method for iterative solutions and behavior of the convergence. Finite-distance effects begin at the third order in the iterative method. The iterative solutions in the strong deflection limit are estimated for Sgr ${\mathrm{A}}^{*}$ and M87. These results suggest that only the linear-order solution can be relevant with current observations, while the finite-distance effects at the third order may be negligible in the Schwarzschild lens model for these astronomical objects.

In general relativity, the spacetimes of black holes have three fundamental properties: (i) they are the same, to the lowest order in spin, as the metrics of stellar objects; (ii) they are independent of mass when expressed in geometric units; and (iii) they are described by the Kerr metric. In this paper, we quantify the upper bounds on potential black-hole metric deviations imposed by observations of black-hole shadows and of binary black-hole inspirals in order to explore the current experimental limits on possible violations of the last two predictions. We find that both types of experiments provide correlated constraints on deviation parameters that are primarily in the $tt$ components of the spacetimes when expressed in areal coordinates. We conclude that, currently, there is no evidence for deviations from the Kerr metric across the 8 orders of magnitude in mass and 16 orders in curvature spanned by the two types of black holes. Moreover, because of the particular masses of black holes in the current sample of gravitational-wave sources, the correlations imposed by the two experiments are aligned and of similar magnitudes when expressed in terms of the far-field, post-Newtonian predictions of the metrics. If a future coalescing black-hole binary with two low-mass (e.g., $\sim 3M_{\odot }$) components is discovered, the degeneracy between the deviation parameters can be broken by combining the inspiral constraints with those from the black-hole shadow measurements.

Motivated by the desire to understand the leading-order nonlinear gravitational wave interactions around arbitrarily rapidly rotating Kerr black holes, we describe a numerical code designed to compute second-order vacuum perturbations on such spacetimes. A general discussion of the formalism we use is presented in [N. Loutrel et al., Phys. Rev. D 103, 104017 (2021)]; here we show how we numerically implement that formalism with a particular choice of coordinates and tetrad conditions and give example results for black holes with dimensionless spin parameters $a=0.7$ and $a=0.998$. We first solve the Teukolsky equation for the linearly perturbed Weyl scalar ${\mathrm{\Psi }}_4^{(1)}$, followed by direct reconstruction of the spacetime metric from ${\mathrm{\Psi }}_4^{(1)}$, and then solve for the dynamics of the second-order perturbed Weyl scalar ${\mathrm{\Psi }}_4^{(2)}$. This code is a first step toward a more general purpose second-order code, and we outline how our basic approach could be further developed to address current questions of interest, including extending the analysis of ringdown in black hole mergers to before the linear regime, exploring gravitational wave “turbulence” around near-extremal Kerr black holes, and studying the physics of extreme mass ratio inspiral.