The decay of $J/\psi$ to three photons is studied using $\psi (3686)\to {\pi }^{+}{\pi }^{-}J/\psi$ in a sample of $1.0641\times {10}^8$ $\psi (3686)$ events collected with the BESIII detector. Evidence of the direct decay of ${\eta }_c$ to two photons, ${\eta }_c\to \gamma \gamma$, is reported, and the product branching fraction is determined to be $\mathcal{B}(J/\psi \to \gamma {\eta }_c,{\eta }_c\to \gamma \gamma )=(4.5\pm 1.2\pm 0.6)\times {10}^{-6}$, where the first error is statistical and the second is systematic. The branching fraction for $J/\psi \to 3\gamma$ is measured to be $(11.3\pm 1.8\pm 2.0)\times {10}^{-6}$ with improved precision.

We construct the isospin particle system on $n$-dimensional quaternionic projective spaces in the presence of the Belavin-Polyakov-Schwarz-Tyupkin instanton by the reduction from the free particle on $(2n+1)$-dimensional complex projective space. Then we add to this system a “quaternionic oscillator potential” and show that this oscillatorlike system is superintegrable. We show that, besides the analogs of quadratic constants of motion of the spherical (Higgs) and $\mathbb{C}{P}^n$ oscillators, it possesses the third-order constants of motion, which are functionally independent from the quadratic ones.

We show that chaotic classical dynamics associated with the volume of discrete grains of space leads to quantal spectra that are gapped between zero and nonzero volume. This strengthens the connection between spectral discreteness in the quantum geometry of gravity and tame ultraviolet behavior. We complete a detailed analysis of the geometry of a pentahedron, providing new insights into the volume operator and evidence of classical chaos in the dynamics it generates. These results reveal an unexplored realm for the application of chaos in quantum gravity.

The Mathisson-Papapetrou equations in Kerr’s background are considered. The region of existence of highly relativistic planar circular orbits of a spinning particle in this background and dependence of the particle’s Lorentz $\gamma$ factor on its spin and radial coordinate are investigated. It is shown that in contrast to the highly relativistic circular orbits of a spinless particle, the corresponding orbits of a spinning particle are allowed in a much wider space region. Some of these orbits show the significant attractive action of the spin-gravity coupling on a particle and others are caused by the significant repulsive action. Numerical estimates for electrons, protons, and neutrinos in the gravitational field of black holes are presented.

We investigate the interaction between dark energy and dark matter in the framework of irreversible thermodynamics of open systems with matter creation/annihilation. We consider dark energy and dark matter as an interacting two-component (scalar field and “ordinary” dark matter) cosmological fluid in a homogeneous spatially flat and isotropic Friedmann-Robertson-Walker Universe. The thermodynamics of open systems as applied together with the gravitational field equations to the two-component cosmological fluid leads to a generalization of the elementary dark energy-dark matter interaction theory, in which the decay (creation) pressures are explicitly considered as parts of the cosmological fluid stress-energy tensor. Specific models describing coherently oscillating scalar waves, leading to a high particle production at the beginning of the oscillatory period, and models with a constant potential energy scalar field are considered. Furthermore, exact and numerical solutions of the gravitational field equations with dark energy-dark matter interactions are also obtained.

We give a detailed discussion of the use of the ($3+1$) decomposition and of Bardeen’s variables in massive gravity linearized over a Minkowski as well as over a de Sitter background. In Minkowski space the Bardeen “potential” $\Phi$, that in the massless case is a nonradiative degree of freedom, becomes radiative and describes the helicity-0 component of the massive graviton. Its dynamics is governed by a simple Klein-Gordon action, supplemented by a term $(\square \Phi {)}^2$ if we do not make the Fierz-Pauli tuning of the mass term. In de Sitter the identification of the variable that describes the radiative degree of freedom in the scalar sector is more subtle, and even involves expressions nonlocal in time. The use of this new variable provides a simple and transparent derivation of the Higuchi bound and of the disappearance of the scalar degree of freedom at a special value of $m_g^2/H^2$. The use of this formalism also allows us to uncover the existence of a hidden gauge symmetry of the massive theory, that becomes manifest only once the nondynamical components of the metric are integrated out, and that is present both in Minkowski and in de Sitter backgrounds.

Recent evidence for one or more gamma-ray lines at $\sim 130\mathrm{GeV}$ in the Fermi-LAT data from the Galactic Center has been interpreted as a hint for dark matter annihilation to $Z\gamma$ or $H\gamma$ with an annihilation cross section of $⟨\sigma v⟩\sim {10}^{-27}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$. We test this hypothesis by comparing synchrotron fluxes due to the electrons and positrons from decay of the $Z$ or the $H$ bosons only against radio data from the same region in the Galactic Center. We find that the radio data from single-dish telescopes marginally constrain this interpretation of the claimed gamma lines for a contracted NFW profile. Already-operational radio telescopes, such as Long Wavelength Array, VLA-Low, and Low-Frequency Array for Radio Astronomy, and future radio telescopes like SKA, are sensitive to annihilation cross sections of the order of ${10}^{-28}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ and can confirm or rule out this scenario very soon. We discuss the dependencies on the dark matter profile, magnetic fields, and background radiation density profiles, and show that the constraints are relatively robust for any reasonable assumptions. Independent of the above said recent developments, we emphasize that our radio constraints apply to all models where dark matter annihilates to $Z\gamma$ or $H\gamma$.

Cosmological constraints on the sum of neutrino masses and on the effective number of neutrino species in standard and nonstandard scenarios are computed using the most recent available cosmological data. Our cosmological data sets include the measurement of the baryonic acoustic oscillation (BAO) feature in the data release 9 CMASS sample of the baryon oscillation spectroscopic survey. We study in detail the different degeneracies among the parameters, as well as the impact of the different data sets used in the analyses. When considering bounds on the sum of the three active neutrino masses, the information in the BAO signal from galaxy clustering measurements is approximately equally powerful as the shape information from the matter power spectrum. The most stringent bound we find is $\sum _{}^{}{m}_{\nu }<0.32\mathrm{eV}$ at 95% C.L. When nonstandard neutrino scenarios with $N_{\mathrm{eff}}$ massless or massive neutrino species are examined, power spectrum shape measurements provide slightly better bounds than the BAO signal only, due to the breaking of parameter degeneracies. Cosmic microwave background data from high multipoles from the South Pole Telescope turns out to be crucial for extracting the number of effective neutrino species. Recent baryon oscillation spectroscopic survey data combined with cosmic microwave background and Hubble Space Telescope measurements give $N_{\mathrm{eff}}={3.66}_{-0.21-0.69}^{+0.20+0.73}$ in the massless neutrino scenario, and similar results are obtained in the massive case. The evidence for extra radiation $N_{\mathrm{eff}}>3$ often claimed in the literature therefore remains at the $2\sigma$ level when considering up-to-date cosmological data sets. Measurements from the Wilkinson Microwave Anisotropy Probe combined with a prior on the Hubble parameter from the Hubble Space Telescope are very powerful in constraining either the sum of the three active neutrino masses or the number of massless neutrino species. If the former two parameters are allowed to freely vary, however, the bounds from the combination of these two cosmological probes get worse by an order of magnitude.

In this paper we discuss a new way to derive neutrino mixing patterns, which originates from the idea proposed in a recent article by Hernandez and Smirnov. Its applications to various cases are discussed. We first present the complete set of possible mixing patterns for the minimal case where unbroken residual symmetries of the Majorana neutrino and left-handed charged-lepton mass matrices obey some general assumptions that are also satisfied by many models based on discrete symmetries. We find that they are either well-known mixing patterns or phenomenologically disfavored ones. It shows clearly that, for full-mixing matrices to fit the mixing data with small or negligible corrections, it is necessary to go beyond the minimal scenario. We present an explicit formalism for a rather general nonminimal case. Some applications and phenomenological implications are discussed. Several new mixing patterns are derived.

We identify a special information-theoretic property of quantum field theories with holographic duals: the mutual informations among arbitrary disjoint spatial regions $A$, $B$, $C$ obey the inequality $I(A:B\cup C)\ge I(A:B)+I(A:C)$, provided entanglement entropies are given by the Ryu-Takayanagi formula. Inequalities of this type are known as monogamy relations and are characteristic of measures of quantum entanglement. This suggests that correlations in holographic theories arise primarily from entanglement rather than classical correlations. We also show that the Ryu-Takayanagi formula is consistent with all known general inequalities obeyed by the entanglement entropy, including an infinite set recently discovered by Cadney et al.; this constitutes strong evidence in favor of its validity.

The standard model of particle physics lies in an enormous number of string vacua. In a nonperturbative formulation of string theory, various string vacua can, in principle, be compared dynamically, and the probability distribution over the vacuum space could be calculated. In this paper, we consider situations where the IIB matrix model is compactified on a six-dimensional torus with various gauge groups and various magnetic fluxes, find matrix configurations that provide the standard model matter content, and estimate semiclassically the probability of their appearance.

We construct the de Sitter QED in Coulomb gauge assuming that the quantum modes are prepared by a global apparatus which is able to determine a stable and invariant vacuum state, independent of the local coordinates. Then we proceed in a traditional manner, postulating the appropriate equal-time commutators and anticommutators of the interacting fields and deriving the perturbation expansion of the scattering operator. In this approach, we consider the in–out transitions amplitudes of the QED on the de Sitter expanding universe. We define the in and out fields as asymptotic-free fields, without electromagnetic interaction but remaining coupled to the de Sitter gravity, assuming that these are measured by the same global apparatus. Then the transition amplitudes can be calculated exactly by using the reduction formalism and the perturbation procedure as in the flat case but with significant differences due to the de Sitter gravity. A specific feature is that this eliminates the constraints due to the simultaneous momentum-energy conservation giving rise to QED transitions with nonvanishing amplitudes even in the first order of perturbations. Of a special interest could be the first order amplitudes of the electromagnetic particle creation allowed by the expansion of the de Sitter universe. We show that this effect is significant only in the very strong gravity of the early universe.

We present a new covariant, gauge-invariant formalism describing linear metric perturbation fields on any spherically symmetric background in general relativity. The advantage of this formalism relies in the fact that it does not require a decomposition of the perturbations into spherical tensor harmonics. Furthermore, it does not assume the background to be vacuum, nor does it require its staticity. In the particular case of vacuum perturbations, we derive two master equations describing the propagation of arbitrary linear gravitational waves on a Schwarzschild black hole. When decomposed into spherical harmonics, they reduce to covariant generalizations of the well-known Regge-Wheeler and Zerilli equations. Next, we discuss the general case where the metric perturbations are coupled to matter fields and derive a new constrained wave system describing the propagation of three gauge-invariant scalars from which the complete metric perturbations can be reconstructed. We apply our formalism to the Einstein-Euler system, dividing the fluid perturbations into two parts. The first part, which decouples from the metric perturbations, obeys simple advection equations along the background flow and describes the propagation of the entropy and the vorticity. The second part describes a perturbed potential flow, and together with the metric perturbations, it forms a closed wave system.

This article introduces a new multipolar hierarchy for the propagation of the weak-lensing shear, convergence, and twist valid in a general spacetime. Our approach is fully covariant and relies on no perturbative expansion. We show that the origin of $B$ modes, in particular on large angular scales, is related to deviations of isotropy of the spacetime. Known results assuming a Friedmann-Lemaître background spacetime are naturally recovered. The example of a Bianchi $I$ spacetime illustrates our formalism and its implications for future observations are stressed.

The global (i.e., spatially averaged) spectrum of the redshifted 21 cm line has generated much experimental interest lately, thanks to its potential to be a direct probe of the epoch of reionization and the dark ages, during which the first luminous objects formed. Since the cosmological signal in question has a purely spectral signature, most experiments that have been built, designed, or proposed have essentially no angular sensitivity. This can be problematic because with only spectral information, the expected global 21 cm signal can be difficult to distinguish from foreground contaminants such as galactic synchrotron radiation, since both are spectrally smooth and the latter is many orders of magnitude brighter. In this paper, we establish a systematic mathematical framework for global signal data analysis. The framework removes foregrounds in an optimal manner, complementing spectra with angular information. We use our formalism to explore various experimental design trade-offs, and find that (1) with spectral-only methods, it is mathematically impossible to mitigate errors that arise from uncertainties in one’s foreground model; (2) foreground contamination can be significantly reduced for experiments with fine angular resolution; (3) most of the statistical significance in a positive detection during the dark ages comes from a characteristic high-redshift trough in the 21 cm brightness temperature; (4) measurement errors decrease more rapidly with integration time for instruments with fine angular resolution; and (5) better foreground models can help reduce errors, but once a modeling accuracy of a few percent is reached, significant improvements in accuracy will be required to further improve the measurements. We show that if observations and data analysis algorithms are optimized based on these findings, an instrument with a 5° wide beam can achieve highly significant detections (greater than $5\sigma$) of even extended (high $\Delta z$) reionization scenarios after integrating for 500 h. This is in strong contrast to instruments without angular resolution, which cannot detect gradual reionization. Ionization histories that are more abrupt can be detected with our fiducial instrument at the level of tens to hundreds of $\sigma$. The expected errors are similarly low during the dark ages, and can yield a $25\sigma$ detection of the expected cosmological signal after only 100 h of integration.

We obtain the in-medium effective potential of the three-flavor Polyakov-quark-meson model as a real function of real variables in the Polyakov loop variable, to allow for the study of all possible minima of the model. At finite quark chemical potential, the real and imaginary parts of the effective potential, in terms of the Polyakov loop variables, are made apparent, showing explicitly the fermion sign problem of the theory. The phase diagram and other equilibrium observables, obtained from the real part of the effective potential, are calculated in the mean-field approximation. The obtained results are compared to those found with the so-called saddle point approach. Our procedure also allows the calculation of the surface tension between the chirally broken and confined phase and the chirally restored and deconfined phase. The values of surface tension we find for low temperatures are very close to the ones recently found for two-flavor chiral models. Some consequences of our results for the early Universe, for heavy-ion collisions, and for proto-neutron stars are discussed.

This paper highlights the predictive power of the three-component Pomeron model designed by the authors ten years ago, with a partial account of the multiplicity of Pomerons in QCD. The model is put to the test by comparing its predictions with the recent data from the D0 and TOTEM collaborations at 1.96 and 7 TeV, respectively. We also compare model predictions for inelastic cross sections to experimental measurements by the TOTEM, CMS, ALICE, and ATLAS collaborations. It is shown that the D0 data are perfectly predicted by the model. Total, elastic, and inelastic cross-section predictions are in agreement with the measurements by the TOTEM, CMS, ALICE, and ATLAS collaborations. Differential cross-section data at 7 TeV show slight disagreement with predictions of the model in the high-$t$ region. Discussions on the origin of the disagreement and conclusions are presented.

We calculate the shear ($\eta$) and bulk ($\zeta$) viscosities of a weakly coupled quark gluon plasma at the leading-log order with finite temperature $T$ and quark chemical potential $\mu$. We find that the shear viscosity to entropy density ratio $\eta /s$ increases monotonically with $\mu$ and eventually scales as $(\mu /T{)}^2$ at large $\mu$. In contrast, $\zeta /s$ is insensitive to $\mu$. Both $\eta /s$ and $\zeta /s$ are monotonically decreasing functions of the quark flavor number $N_f$ when $N_f\ge 2$. This property is also observed in pion gas systems. Our perturbative calculation suggests that QCD becomes the most perfect (i.e. with the smallest $\eta /s$) at $\mu =0$ and $N_f=16$ (the maximum $N_f$ with asymptotic freedom). It would be interesting to test whether the currently smallest $\eta /s$ computed close to the phase transition with $\mu =0$ and $N_f=0$ can be further reduced by increasing $N_f$.

We analyze the prospective impact of supersymmetric radiative corrections on tests of charged current universality involving light quarks and leptons. Working within the $R$-parity conserving minimal supersymmetric Standard Model, we compute the corresponding one-loop corrections that enter the extraction of the Cabibbo-Kobayashi-Maskawa matrix element $V_{ud}$ from a comparison of the muon-decay Fermi constant with the vector coupling constant determined from nuclear and neutron $\beta$ decay. We also revisit earlier studies of the corrections to the ratio $R_{e/\mu }$ of pion leptonic decay rates $\Gamma [{\pi }^{+}\to e^{+}\nu (\gamma )]$ and $\Gamma [{\pi }^{+}\to {\mu }^{+}\nu (\gamma )]$. In both cases, we observe that the magnitude of the corrections can be on the order of ${10}^{-3}$. We show that a comparison of the first row Cabibbo-Kobayashi-Maskawa unitarity tests with measurements of $R_{e/\mu }$ can provide unique probes of the spectrum of first generation squarks and first and second generation sleptons.