High-statistics data on the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ cross section and the pion vector form factor have been obtained recently by several collaborations. Unfortunately, there are some tensions between different data sets, especially the most precise ones, which have not been resolved so far. Additional independent constraints on the data are therefore of interest. We consider a parametrization-free method of analytic extrapolation proposed recently, which is based on a mixed phase and modulus extremal problem and combines rigorous upper and lower bounds with numerical simulations to account for the statistical distributions of the input and output values. Spacelike data on the form factor and measurements of the modulus in the region (0.65–0.71) GeV are used as input. In previous works, the formalism was applied for extrapolating the form factor to low energies. In the present work, we use it as a stringent and model-independent test of consistency with analyticity and unitarity for the high-statistics data around the $\rho$ resonance. The study reveals some inconsistencies, in particular, below the $\rho$ peak, the BABAR data are slightly higher than the band of extrapolated values, while above the $\rho$ peak, all the data are situated at the lower edge of the band. The implications of the results on the two-pion vacuum polarization contribution to the anomalous magnetic moment of the muon are briefly discussed.

A second gradient generalization of Newtonian gravity is presented within the framework of gradient field theory. Weak nonlocality is introduced via first and second gradients of the gravitational field strength in the Lagrangian density. Gradient generalizations of the Poisson equation of Newtonian gravitation for the gravitational potential and of the generalized Gauss law for the gravitational field strength are presented. Such a gradient modification of Newtonian gravity provides a straightforward regularization of Newtonian gravity removing the classical Newtonian singularities. Finite gradient modifications of the gravitational potential energy and of the gravitational force law are constructed, with a possible connection to Yukawa interaction, and as suitable candidates for experimental tests of Newton’s inverse-square law at short distances. In addition, nonlocal gravity of exponential type is investigated and its relation to gradient gravity theory is given.

We explore artificial neural networks as a tool for the reconstruction of spectral functions from imaginary time Green’s functions, a classic ill-conditioned inverse problem. Our ansatz is based on a supervised learning framework in which prior knowledge is encoded in the training data and the inverse transformation manifold is explicitly parametrized through a neural network. We systematically investigate this novel reconstruction approach, providing a detailed analysis of its performance on physically motivated mock data, and compare it to established methods of Bayesian inference. The reconstruction accuracy is found to be at least comparable and potentially superior in particular at larger noise levels. We argue that the use of labeled training data in a supervised setting and the freedom in defining an optimization objective are inherent advantages of the present approach and may lead to significant improvements over state-of-the-art methods in the future. Potential directions for further research are discussed in detail.

We consider simple scalar theories with quadratic terms that are nonlocal and Lorentz violating. Unlike similar Lorentz-invariant nonlocal theories that we have considered previously, the theories studied here are both ghost-free and unitary as formulated in Minkowski space. We explore the possibility that the scale of nonlocality could be low in a dark sector, where the stringent constraints on the violation of Lorentz invariance may be accommodated via the weak coupling to the standard model. We point out that long-range forces may originate from such a sector and be distinguishable from more conventional beyond-the-standard-model possibilities. We present a model in which a nonlocal, Lorentz-violating dark sector communicates with the standard model via a sector of heavy vectorlike fermions, a concrete framework in which phenomenological constraints and signals can be investigated.

Lattice QCD calculations using gauge smearing for fermion kernels are computationally efficient. Hypercubic blocking (nHYP smearing) has been shown to reduce scaling errors. In this work we use an improved action for $N_f=2$ QCD, based on the Lüscher-Weisz gauge action and clover-improved Wilson fermions with nHYP smeared gauge links. We perform a parameter scan in the region with lattice spacing between 0.066 fm and 0.115 fm and pion mass between 207 MeV and 834 MeV. We determine the lattice spacing and pion mass as a function of the bare coupling parameters ($\beta$ and $\kappa$). The results are obtained from 22 ensembles on a ${24}^3\times 48$ lattice to the percent level in statistical accuracy. The finite-volume effects for these ensembles are at the subpercent level. From these measurements we produce easy-to-use parametrizations to help tune simulations with this action. The lattice spacing is fixed using a mass-independent procedure, by matching observables in the chiral limit. We also provide a parametrization for the chiral extrapolation which is universal and should hold for all discretizations of $N_f=2$ QCD.

We explore connections between high energy QCD spin physics and $CP$-odd scalar gluonic operators ${\tilde{F}}^{\mu \nu }{F}_{\mu \nu }$ and ${\tilde{F}}_{\mu \nu }{F}^{\mu \alpha }{F}_{\alpha }^{\nu }$, the latter being called the Weinberg operator in the context of the nucleons’ electric dipole moment. We first introduce the twist-four generalized parton distribution associated with the topological operator $F_{\mu \nu }{\tilde{F}}^{\mu \nu }$. This has interesting applications in spin physics which go beyond the standard framework in terms of twist-two and twist-three distributions. In the second part, we show that the off-forward matrix element of the Weinberg operator is proportional to a certain twist-four correction to the $g_1$ structure function in polarized deep inelastic scattering.

We analyze the electromagnetic current correlator at an arbitrary photon invariant mass $q^2$ by exploiting its associated dispersion relation. The dispersion relation is turned into an inverse problem, by which the involved vacuum polarization function $\mathrm{\Pi }(q^2)$ at low $q^2$ is solved with the perturbative input of $\mathrm{\Pi }(q^2)$ at large $q^2$. It is found that the result for $\mathrm{\Pi }(q^2)$, including its first derivative ${\mathrm{\Pi }}^{\prime }(q^2=0)$, agrees with those from lattice QCD, and its imaginary part accommodates the $e^{+}{e}^{-}$-annihilation data. The corresponding hadronic vacuum polarization (HVP) contribution $a_{\mu }^{\mathrm{HVP}}=(641_{-63}^{+65})\times {10}^{-10}$ to the muon anomalous magnetic moment $g-2$, where the uncertainty arises from the variation of the perturbative input, also agrees with those obtained in other phenomenological and theoretical approaches. We point out that our formalism is equivalent to imposing the analyticity constraint to the phenomenological approach solely relying on experimental data and can improve the precision of the $a_{\mu }^{\mathrm{HVP}}$ determination in the Standard Model.

As a result of a nontrivial mixing matrix, neutrinos cannot be simultaneously in a flavor and mass eigenstate. We formulate and discuss information entropic relations that quantify the associated quantum uncertainty. We also formulate a protocol to determine the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix from quantum manipulations and measurements on an entangled lepton-neutrino pair. The entangled state features neutrino oscillations in a conditional probability involving measurements on the lepton and the neutrino. They can be switched off by choosing a specific observable on the lepton side which is determined by the PMNS matrix. The parameters of the latter, including the $CP$-violating phase $\delta$, can be obtained by guessing them and improving the guess by minimizing the remaining oscillations.

The Deep Underground Neutrino Experiment is a next-generation neutrino oscillation experiment that aims to measure $CP$-violation in the neutrino sector as part of a wider physics program. A deep learning approach based on a convolutional neural network has been developed to provide highly efficient and pure selections of electron neutrino and muon neutrino charged-current interactions. The electron neutrino (antineutrino) selection efficiency peaks at 90% (94%) and exceeds 85% (90%) for reconstructed neutrino energies between 2–5 GeV. The muon neutrino (antineutrino) event selection is found to have a maximum efficiency of 96% (97%) and exceeds 90% (95%) efficiency for reconstructed neutrino energies above 2 GeV. When considering all electron neutrino and antineutrino interactions as signal, a selection purity of 90% is achieved. These event selections are critical to maximize the sensitivity of the experiment to $CP$-violating effects.

A measurement of the $W^{+}{W}^{-}$ boson pair production cross section in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ is presented. The data used in this study are collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of $35.9{\mathrm{fb}}^{-1}$. The $W^{+}{W}^{-}$ candidate events are selected by requiring two oppositely charged leptons (electrons or muons). Two methods for reducing background contributions are employed. In the first one, a sequence of requirements on kinematic quantities is applied allowing a measurement of the total production cross section, $117.6\pm 6.8\mathrm{pb}$, which agrees well with the theoretical prediction. Fiducial cross sections are also reported for events with zero or one jet, and the change in the zero-jet fiducial cross section with the jet transverse momentum threshold is measured. Normalized differential cross sections are reported within the fiducial region. A second method for suppressing background contributions employs two random forest classifiers. The analysis based on this method includes a measurement of the total production cross section and also a measurement of the normalized jet multiplicity distribution in $W^{+}{W}^{-}$ events. Finally, a dilepton invariant mass distribution is used to probe for physics beyond the standard model in the context of an effective field theory, and constraints on the presence of dimension-6 operators are derived.

Very recently the LHCb Collaboration reported the discovery of two open charm tetraquark states, $X_0(2866)$ and $X_1(2904)$. In the present work, we study the $D^{(*)}$ and ${\overline{K}}^{(*)}$ interaction in the one-boson exchange model and show that $X_0(2866)$ can be understood as a $D^{*}{\overline{K}}^{*}$ molecule with $I(J^P)=0(0^{+})$, or at least it has a large molecular component. On the other hand, $X_1(2904)$ can not be interpreted as a molecular state. Inspired by the discovery of $X_0(2866)$ and the fact that the $D^{*}{\overline{K}}^{*}$ interaction is strong enough to generate a bound state, we also discuss the likely existence of other open charm molecules. In the meson-meson sector, two molecules near the mass thresholds of $D{D}^{*}$ and $D^{*}{D}^{*}$ with $I(J^P)=0(1^{+})$ are obtained, and using the heavy quark flavor symmetry their $\overline{B}{\overline{B}}^{*}$ and ${\overline{B}}^{*}{\overline{B}}^{*}$ counterparts are also predicted. In the meson-baryon sector, seven open charm molecules with $I=1/2$ near the mass thresholds of $D^{(*)}{\mathrm{\Sigma }}_c^{(*)}$ naturally appear, as dictated by the heavy quark spin symmetry.

We calculate the thermal rate of real-photon production in the quark-gluon plasma at a temperature of $T=254\mathrm{MeV}$ using lattice QCD. The calculation is based on the difference between the spatially transverse and longitudinal parts of the polarization tensor, which has the advantage of falling off rapidly at large frequencies. We obtain this linear combination in the time-momentum representation from lattice QCD with two flavors of quarks in the continuum limit with a precision of about two parts per mille. Applying a theoretically motivated fit ansatz for the associated spectral function, we obtain values for the photon rate that are in line with QCD weak-coupling calculations. A representative result is $d\mathrm{\Gamma }(k)/dk=(1.5_{-1.5}^{+2.1})·(10\mathrm{fm}{)}^{-4}·(0.2\mathrm{GeV}{)}^{-1}$ at $k=1.2\mathrm{GeV}$ for the differential rate of photon production per unit volume of plasma.

This paper contains discussions on the entanglement entropy and mutual information of a strongly coupled field theory with a critical point which has a holographic dual. We investigate analytically, in the specific regimes of parameters, how these nonlocal operators behave near the critical point. Interestingly, we observe that although the mutual information is constant at the critical point, its slope shows a power-law divergence in the vicinity of the critical point. We show that the leading behavior of mutual information at and near the critical point could yield a set of critical exponents if we regard it as an order parameter. Our result for this set of static critical exponents is $(1/2,1/2,1/2,2)$ which is identical to the one calculated via the thermodynamic quantities. Hence it suggests that beside the numerous merits of mutual information, this quantity also captures the critical behavior of the underlying field theory and it could be used as a proper measure to probe the phase structure associated with the strongly coupled systems.

The third release of the RIT public catalog of numerical relativity black-hole-binary waveforms http://ccrg.rit.edu/~RITCatalog consists of 777 accurate simulations that include 300 precessing and 477 nonprecessing binary systems with mass ratios $q=m_1/m_2$ in the range $1/15\le q\le 1$ and individual spins up to $s/m^2=0.95$. 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. We successfully test this correction comparing with simulations of low radiation content initial data. As an initial application of this waveform catalog we reanalyze all the peak radiation and remnant properties to find new, simple, correlations among them for practical astrophysical usage.

We present the second-order gravitational dynamics for a spacetime inhabited by matter fields which feature vacuum birefringence. The derivation follows a perturbative variant of the covariant constructive gravity program, ensuring diffeomorphism invariance of gravity and causal compatibility of matter theory and gravity. A subsequent spatiotemporal split of this theory reveals the presence of unphysical artifacts, which are cured by imposing constraints on the gravitational constants, reducing their number from ten to seven. Within this sector, we derive the gravitational radiation emitted by a binary system in circular motion. The system emits massless waves, which correspond to the radiation predicted by Einstein gravity, but also massive waves, which are generated only above a certain angular frequency threshold and are unknown to Einstein gravity. A gravitational-wave detector modeled as a sphere of freely falling test masses shows quantitatively and qualitatively new behavior under the influence of this radiation. The result is a prediction of gravitational self-coupling from first principles, demonstrating the predictive power of covariant constructive gravity for modified gravity research, especially in the era of gravitational-wave astronomy.

We demonstrate the existence of static stable spherical fluid shells in the Schwarzschild-Rindler–anti–de Sitter (SRAdS) spacetime where $d{s}^2=f(r)d{t}^2-\frac{d{r}^2}{f(r)}-r^2(d{\theta }^2+{\sin }^2\theta d{\varphi }^2)$ with $f(r)=1-\frac{2Gm}{r}+2br-\frac{\mathrm{\Lambda }}{3}{r}^2$. This is an alternative to the well-known gravastar geometry where the stability emerges due to the combination of the repulsive forces of the interior de Sitter space with the attractive forces of the exterior Schwarzschild spacetime. In the SRAdS spacetime the repulsion that leads to stability of the shell comes from a negative Rindler term while the Schwarzschild and anti–de Sitter terms are attractive. We demonstrate the existence of such stable spherical shells for three shell fluid equations of state: vacuum shell ($p=-\sigma$), stiff matter shell ($p=\sigma$) and dust shell ($p=0$) where $p$ is the shell pressure and $\sigma$ is the shell surface density. We also identify the metric parameter conditions that need to be satisfied for shell stability in each case. The vacuum stable shell solution in the SRAdS spacetime is consistent with previous studies by two of the authors that demonstrated the existence of stable spherical scalar field domain walls in the SRAdS spacetime.

Numerical-relativity simulations are essential for studying the last stages of the binary neutron star coalescence. Unfortunately, for stable simulations there is the need to add an artificial low-density atmosphere. Here we discuss a new framework in which we can effectively set the density surrounding the neutron stars to zero to ensure a more accurate simulation. We test our method with a number of single star test cases and for an equal-mass binary neutron star simulation. While the bulk motion of the system is not influenced, and hence there is no improvement with respect to the emitted gravitational-wave signal, we find that the new approach is superior with respect to mass conservation and it allows a much better tracking of outward moving material. This will allow a more accurate simulation of the ejected material and supports the interpretation of present and future multimessenger observations with more accurate numerical-relativity simulations.

We suggest a new thermodynamic curvature, constructed via adiabatic compressibility, for examining the internal microstructure of charged black holes in an anti-de Sitter background. We analyze the microscopic properties of small-large phase transition of black holes with pressure and volume as the fluctuation variables. We observe that strong repulsive interactions dominate among the microstructures of near extremal small black holes, and the thermodynamic curvature diverges to positive infinity for the extremal black holes. At the critical point, however, thermodynamic curvature diverges to negative infinity.

We study the structure and stability of traversable wormholes built as (spherically symmetric) thin shells in the context of Palatini $f(\mathcal{R})$ gravity. Using a suitable junction formalism for these theories we find that the effective number of degrees of freedom on the shell is reduced to a single one, which fixes the equation of state to be that of massless stress-energy fields, contrary to the general relativistic and metric $f(R)$ cases. Another major difference is that the surface energy density threading the thin shell, needed in order to sustain the wormhole, can take any sign and may even vanish, depending on the desired features of the corresponding solutions. We illustrate our results by constructing thin-shell wormholes by surgically grafting Schwarzschild space-times and show that these configurations are always linearly unstable. However, surgically joined Reissner-Nordström space-times allow for linearly stable, traversable thin-shell wormholes supported by a positive energy density provided that the (squared) mass-to-charge ratio, given by $y=Q^2/M^2$, satisfies the constraint $1<y<9/8$ (corresponding to overcharged Reissner-Nordström configurations having a photon sphere) and lies in a region bounded by specific curves defined in terms of the (dimensionless) radius of the shell $x_0=R/M$.

Universal relations and constants have important applications in understanding a physical theory. In this article, we explore this issue for Hawking-Page phase transitions in Schwarzschild anti–de Sitter black holes. We find a novel exact dual relation between the minimum temperature of the ($d+1$)-dimensional black hole and the Hawking-Page phase transition temperature in $d$ dimensions, reminiscent of the holographic principle. Furthermore, we find that the normalized Ruppeiner scalar curvature is a universal constant at the Hawking-Page transition point. Since the Ruppeiner curvature can be treated as an indicator of the intensity of the interactions amongst black hole microstructures, we conjecture that this universal constant denotes an interaction threshold, beyond which a virtual black hole becomes a real one. This new dual relation and universal constant are fundamental in understanding Hawking-Page phase transitions, and might have new important applications in the black hole physics in the near future.