We consider the decay ${\pi }^{-}\to l{\overline{\nu }}_l$ ($l=e^{-},{\mu }^{-}$) in the presence of an arbitrary large uniform magnetic field, using the symmetric gauge. The consequences of the axial symmetry of the problem and the issue of angular momentum conservation are discussed in detail. In particular, we analyze the projection of both the canonical and the mechanical total angular momenta along the direction of the magnetic field. It is found that while the former is conserved in the symmetric gauge, the latter is not conserved in both the symmetric and Landau gauges. We derive an expression for the integrated ${\pi }^{-}\to l{\overline{\nu }}_l$ width that coincides exactly with the one we previously found using the Landau gauge, providing an explicit test of the gauge independence of that result. Such an expression implies that for nonzero magnetic fields the decay width does not vanish in the limit in which the outgoing charged leptons can be considered as massless, i.e., it does not exhibit the helicity suppression found in the case of no external field.

We construct hyperasymptotic expansions for the heavy quark pole mass regulated using the principal value (PV) prescription. We apply such hyperasymptotic expansions to the $B/D$ meson masses, and $\overline{\mathrm{\Lambda }}$ computed in the lattice. The issue of the uncertainty of the (top) pole mass is critically reexamined. The present theoretical uncertainty in the relation between ${\overline{m}}_t$, the $\overline{\mathrm{MS}}$ top mass, and $m_{t,\mathrm{PV}}$, the top pole mass regulated using the PV prescription, is numerically assessed to be $\delta m_{t,\mathrm{PV}}=28\mathrm{MeV}$ for ${\overline{m}}_t=163\mathrm{GeV}$.

In this work, we present the mass spectrum of higher charmonia around and above 4.6 GeV by adopting the unquenched potential model. We perform a combined fit to the updated experimental data of $e^{+}{e}^{-}\to \psi (2S){\pi }^{+}{\pi }^{-}$ and $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c{\overline{\mathrm{\Lambda }}}_c$. To understand the “platform” structure observed in the range of 4.57–4.60 GeV existing in the ${\mathrm{\Lambda }}_c{\overline{\mathrm{\Lambda }}}_c$ invariant mass spectrum of $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c{\overline{\mathrm{\Lambda }}}_c$ of BESIII, we introduce two resonances in this combined fit to $e^{+}{e}^{-}\to \psi (2S){\pi }^{+}{\pi }^{-}$ and $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c{\overline{\mathrm{\Lambda }}}_c$, which have resonance parameters, $m_{Y_1}=4585\pm 2\mathrm{MeV}$, ${\mathrm{\Gamma }}_{Y_1}=29.8\pm 8.0\mathrm{MeV}$, $m_{Y_2}=4676\pm 7\mathrm{MeV}$, and ${\mathrm{\Gamma }}_{Y_2}=85.7\pm 15.0\mathrm{MeV}$. Furthermore, combining with our theoretical results, we indicate that the two charmoniumlike $Y$ states can be due to two higher charmonia, which are mixtures of $6S$ and $5D$ $c\overline{c}$ states. Their two-body open-charm decay behaviors are given. Under the same framework, our analysis of the data of $e^{+}{e}^{-}\to D_s^{+}{D}_{s1}(2536{)}^{-}$ recently released by Belle supports the introduction of these two higher charmonia around 4.6 GeV. Additionally, we predict the masses and two-body open-charm decays of six higher charmonia $\psi (nS)$ and $\psi (mD)$ with $n=7$, 8, 9 and $m=6$, 7, 8 above 4.6 GeV. The search for these higher charmonia will be an interesting issue for the running BESIII and BelleII, and even the possible Super Tau-Charm Factory discussed in China.

We study the feasibility of using neutrino-electron elastic scattering to measure the neutrino flux in the DUNE neutrino oscillation experiment. The neutrino-electron scattering cross section is precisely known, and the kinematics of the reaction allow the determination of the incoming neutrino energy by precise measurement of the energy and angle of the recoiling electron. For several possible near detectors, we perform an analysis of their ability to measure neutrino flux in the presence of backgrounds and uncertainties. With realistic assumptions about detector masses, we find that a liquid argon detector, even with limitations due to angular resolution, is able to perform better than less dense detectors with more precise event-by-event neutrino energy measurements. We find that the absolute flux normalization uncertainty can be reduced from $\sim 8\%$ to $\sim 2\%$, and the uncertainty on the flux shape can be reduced by $\sim 20\%–30\%$.

Using a sample of $1.31\times {10}^{9}J/\psi$ events collected with the BESIII detector, we perform a search for the rare decay ${\eta }^{\prime }\to 4{\pi }^0$ via $J/\psi \to \gamma {\eta }^{\prime }$. No significant ${\eta }^{\prime }$ signal is observed in the $4{\pi }^0$ invariant mass spectrum. With a Bayesian approach, the upper limit on the branching fraction is determined to be $\mathcal{B}({\eta }^{\prime }\to 4{\pi }^0)<4.94\times {10}^{-5}$ at the 90% confidence level, which is a factor of 6 smaller than the previous experimental limit.

In this paper, the gravitational deflection of relativistic massive particles up to the second post-Minkowskian order by static and spherically symmetric wormholes is investigated in the weak-field limit. These wormholes include the Janis-Newman-Winicour wormhole, a class of zero Ricci scalar scalar-tensor wormholes, and a class of charged Einstein-Maxwell-dilaton wormholes. With the Jacobi metric approach, the Gauss-Bonnet theorem is employed to study the gravitational deflection. In this scheme, the deflection angle as a topological effect is considered. Moreover, we analyze the influence of the spacetime parameters on the results.

We consider the gravitational analogue of Lyman-alpha absorption lines in astronomical spectroscopy. If Einstein gravity with minimally coupled matter is valid up to the Planck scale, quantum bound states absorb gravitons of a specific frequency with Planckian cross section, ${\sigma }_{\mathrm{abs}}\approx l_p^2$. Consequently, one can show that gravitational absorption by bound states is inefficient in ordinary gravity. If observed, gravitational absorption lines would therefore constitute a powerful smoking gun of new exotic astrophysical bound states (near extremal bound states) or new gravitational physics, as well as give direct evidence of the quantized nature of the gravitational field. We provide, as an example of new gravitational physics near the Planck scale, a nonminimal coupling of the matter fields which breaks the equivalence principle on-shell. We lay out a model in which absorption lines in the primordial gravitational wave spectrum are produced as a consequence of this coupling.

In the present paper, we study the capability of interacting dark energy model with pure momentum transfer in the dark sector to reconcile tensions between low redshift observations and cosmic microwave background (CMB) results. This class of interacting model with pure momentum exchange introduces modifications to the standard model in the level of perturbation. We investigate the model by comparing to observational data, including integrated Sachs-Wolfe-galaxy cross-correlation, galaxy power spectrum, $f{\sigma }_8$, and CMB data. It is shown that this model can alleviate the observed tension between local and global measurements of ${\sigma }_8$. According to our results, the best fit value of ${\sigma }_8$ for interacting model is 0.700, which is lower than the one for $\mathrm{\Lambda }\mathrm{CDM}$ model and also is consistent with low redshift observations. Furthermore, we perform a forecast analysis to find the constraints on parameters of the interacting model from future experiments.

We analyze the zero point energy of composite particles (or resonances) which are dynamically created from relativistic fermions. We compare the zero point energies in medium to the vacuum one, taking into account the medium modification of the constituent particles. Treating composite particles as if quasiparticles, their zero point energies contain the quadratic and logarithmic UV divergences even after the vacuum subtraction. The coefficients of these divergences come from the difference between the vacuum and in-medium fermion propagators. We argue that such apparent divergences can be cancelled by consistently using fermion propagators to compute the quasi-particle contributions as well as their interplay, provided that the self-energies of the constituents at large momenta approach to the vacuum ones sufficiently fast. In the case of quantum chromodynamics, mesons and baryons, which may be induced or destroyed by medium effects, yield the in-medium divergences in the zero point energies, but the divergences are assembled to cancel with those from the quark zero-point energy. This is particularly important for unified descriptions of hadronic and quark matter which may be smoothly connected by the quark-hadron continuity.

Recently, Risaliti and Lusso [Nat. Astron. 3, 272 (2019)] reported new measurements of the expansion rate of the Universe by constructing the  Hubble diagram of 1598 quasars in the redshift range $0.5<z<5.5$. It is claimed a $4\sigma$ tension with the standard concordance $\mathrm{\Lambda }\mathrm{CDM}$ concerning both the fractionary matter density ${\mathrm{\Omega }}_{m0}$ and the dark energy equation of state parameter $w_{\mathrm{de}}$ standard values. In this work we promote an independent analysis of the same data set using a model-independent estimator for cosmic acceleration. Our results corroborate that the source of such tension can be related to the ${\mathrm{\Omega }}_{m0}$ value with a reasonable indication of a higher ${\mathrm{\Omega }}_{m0}$ value (${\mathrm{\Omega }}_{m0}\gtrsim 0.4$). On the other hand, we find that the role played by $w_{\mathrm{de}}$ on the claimed tension is weak. We also discuss the use of this estimator as a “quality tool” to test the robustness of Hubble diagrams. We conclude claiming that the quasars data cannot yet be seen as a reliable cosmological tool since they cannot even state the universe experienced an accelerated expansion phase.

We study string inspired two-field models of large-field inflation based on axion monodromy in the presence of an interacting heavier modulus. This class of models has enough structure to approximate at least part of the backreaction effects known in full string theory, such as kinetic mixing with the axion, and flattening of the scalar potential. Yet, it is simple enough to fully describe the structure of higher-point curvature perturbation interactions driven by the adjusting modulus backreaction dynamics. We find that the presence of the heavy modulus can be described via two equivalent effective field theories, both of which can incorporate reductions of the speed of sound. Hence, the presence of heavier moduli in axion monodromy inflation constructions will necessarily generate some amount of non-Gaussianity accompanied by changes to $n_s$ and $r$ beyond what results from just from the well-known adiabatic flattening backreaction.

We study pseudo-Goldstone dark matter in the ${\mathbb{Z}}_3$ complex scalar singlet model. Because the direct detection spin-independent cross section is suppressed, such dark matter is allowed in a large mass range. Unlike in the original model stabilized by a parity and due to the cubic coupling of the singlet, the ${\mathbb{Z}}_3$ model can accommodate first-order phase transitions that give rise to a stochastic gravitational wave signal potentially observable in future space-based detectors.

We present a study of a $1+1$ dimensional heavy-light three-body system in finite volume. The heavy-light system is simulated by a coupled-channel ${\varphi }^4$ type lattice model, and both ground state and excited states of multiparticle energy spectra are measured on various lattices. The lattice simulation data analysis is performed based on a variational approach.

By simulating the finite temperature magnetized background at the Relativistic Heavy Ion Collider and LHC energies, we systematically study the characteristics of the thermal width and potential of heavy quarkonia. It is found that the magnetic field has less influence on the real potential but has a significant influence on the imaginary potential, especially in the low deconfined temperature. Extracted from the effect of thermal worldsheet fluctuations about the classical configuration, the thermal width of $\mathrm{\Upsilon }(1S)$ at the finite temperature magnetized background is investigated. It is found that at the low deconfined temperature the magnetic field can generate a significant thermal fluctuation of the thermal width of $\mathrm{\Upsilon }(1S)$, but with the increase of temperature, the effect of magnetic field on the thermal width becomes less important, which means the effect of high temperature completely exceeds that of magnetic field and magnetic field becomes less important at high temperature. The thermal width decreases with the increasing rapidity at the finite temperature magnetized background. It is also observed that the effect of the magnetic field on the thermal width when the dipole is moving perpendicular to the magnetic field is larger than that moving parallel to the magnetic field at $T_c<T<1.5T_c$, which implies that the magnetic field tends to enhance thermal fluctuation when the dipole is moving perpendicular to magnetic field, but when $T>2T_c$, the effect of magnetic field on the thermal fluctuation is almost the same whether dipole moving perpendicular or parallel to the magnetic field.

We review the covariant canonical formalism initiated by D’Adda, Nelson, and Regge in 1985, and extend it to include a definition of form-Poisson brackets (FPBs) for geometric theories coupled to $p$-forms. The form-Legendre transformation and the form-Hamilton equations are derived from a $d$-form Lagrangian with $p$-form dynamical fields $\varphi$. Momenta are defined as derivatives of the Lagrangian with respect to the “velocities” $d\varphi$ and no preferred time direction is used. Action invariance under infinitesimal form-canonical transformations can be studied in this framework, and a generalized Noether theorem is derived, for both global and local symmetries. We apply the formalism to vielbein gravity in $d=3$ and $d=4$. In the $d=3$ theory we can define form-Dirac brackets, and use an algorithmic procedure to construct the canonical generators for local Lorentz rotations and diffeomorphisms. In $d=4$ the canonical analysis is carried out using FPBs, since the definition of form-Dirac brackets is problematic. Lorentz generators are constructed, while diffeomorphisms are generated by the Lie derivative. A “doubly covariant” Hamiltonian formalism is presented, allowing to maintain manifest Lorentz covariance at every stage of the Legendre transformation. The idea is to take curvatures as “velocities” in the definition of momenta.

The semiclassical gravity describes gravitational backreactions of the classical spacetime interacting with quantum matter fields, but the quantum effects on the background are formally defined as higher-derivative curvatures. These induce catastrophic instabilities and classic solutions become unstable under small perturbations or their evolutions. In this paper, we discuss validity of the semiclassical gravity from the perspective of the spacetime instabilities and consider cosmological dynamics of the Universe in this theory. We clearly show that the homogenous and isotropic flat Universe is unstable and the solutions either grow exponentially or oscillate even in Planckian time $t_{\mathrm{I}}=({\alpha }_1{G}_N{)}^{1/2}\approx {\alpha }_1{10}^{-43}\sec$. The subsequent curvature evolution leads to Planck-scale spacetime curvature in a short time and causes a catastrophe of the Universe unless one takes extremely large values of the gravitational couplings. Furthermore, we confirm the above suggestion by comparing the semiclassical solutions and $\mathrm{\Lambda }\mathrm{CDM}$ with the Planck data and it is found that the semiclassical solutions are not consistent with the cosmological observations. Thus, the standard semiclassical gravity using quantum energy momentum tensor $⟨T_{\mu \nu }⟩$ is not appropriate to describe our Universe.

We propose a new model for the description of a gravitating multiparticle system, viewed as a kinetic gas. The properties of the (colliding or noncolliding) particles are encoded into a so-called one-particle distribution function, which is a density on the space of allowed particle positions and velocities, i.e., on the tangent bundle of the spacetime manifold. We argue that an appropriate theory of gravity, describing the gravitational field generated by a kinetic gas, must also be modeled on the tangent bundle. The most natural mathematical framework for this task is Finsler spacetime geometry. Following this line of argumentation, we construct a coupling between the kinetic gas and a recently proposed Finsler geometric extension of general relativity. Additionally, we explicitly show how the general covariance of the action of the kinetic gas on the tangent bundle leads to a novel formulation of its energy-momentum conservation in terms of its energy-momentum distribution tensor.

We present an approach to the parametrized post-Newtonian (PPN) formalism which is based on gauge-invariant higher order perturbation theory. This approach divides the components of the metric perturbations into gauge-invariant quantities, which carry information about the physical system under consideration, and pure gauge quantities, which describe the choice of the coordinate system. This separation generally leads to a simplification of the PPN procedure, since only the gauge-invariant quantities appear in the field equations and must be determined by solving them. Another simplification arises from the fact that the gauge-invariant approach supersedes the necessity to first choose a gauge for solving the gravitational field equations and later transforming the obtained solution into the standard PPN gauge, as it is conventionally done in the PPN formalism, whose standard PPN gauge is determined only after the full solution is known. In addition to the usual metric formulation, we also present a tetrad formulation of the gauge-invariant PPN formalism. To illustrate their practical application, we demonstrate the calculation of the PPN parameters of a well-known scalar-tensor class of theories.

A novel criterion to determine the presence of gravitational radiation arriving to, or departing from, null infinity of any weakly asymptotically simple spacetime with vanishing cosmological constant is given. The quantities involved are geometric, of tidal nature, with good gauge behavior and univocally defined at null infinity. The relationship with the classical characterization using the news tensor is analyzed in detail. A new balance law at infinity is presented, which may be useful to define “radiation states.”