An experimental study of the ${\eta }^{\prime }\to {\pi }^0{\pi }^0\eta \to 6\gamma$ decay has been conducted with the best up-to-date statistical accuracy, by measuring ${\eta }^{\prime }$ mesons produced in the $\gamma p\to {\eta }^{\prime }p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the ${\eta }^{\prime }\to {\pi }^0{\pi }^0\eta$ matrix element are consistent with the most recent results for ${\eta }^{\prime }\to \pi \pi \eta$ decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the ${\pi }^{+}{\pi }^{-}$ mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the $\pi \pi$ scattering length combination, $a_0-a_2$, extracted from $K\to 3\pi$ decays.

We study holographic entanglement entropy in spatially anisotropic field theory. We observe that for the background considered in this paper, to a good approximation, the holographic entanglement entropy can be decomposed into two terms. One of them is the entanglement entropy of the isotropic field theory at a fixed temperature and the other term is only a function of the anisotropy parameter. Moreover, for large enough values of the anisotropy parameter, our numerical results indicate that the entanglement entropy in the perpendicular direction to the anisotropic direction is greater than the parallel case.

In a spin-network basis state, nodes of the graph describe unentangled quantum regions of space, quantum polyhedra. In this paper we show how entanglement between intertwiner degrees of freedom enforces gluing conditions for neighboring quantum polyhedra. In particular, we introduce Bell-network states, entangled states defined via squeezed vacuum techniques. We study correlations of quantum polyhedra in a dipole, a pentagram, and a generic graph. We find that vector geometries, structures with neighboring polyhedra having adjacent faces glued back to back, arise from Bell-network states. We also discuss the relation to Regge geometries. The results presented show clearly the role that entanglement plays in the gluing of neighboring quantum regions of space.

We study the entanglement dynamics for two uniformly accelerated two-level atoms in interaction with a bath of fluctuating electromagnetic fields in vacuum in the presence of a reflecting boundary. We consider two different alignments of atoms, i.e., parallel and vertical alignments with respect to the boundary. In particular, we focus on the effects of the boundary, and acceleration on the entanglement dynamics, which are closely related to the orientations of polarization. For the parallel case, the initial entanglement of two transversely polarizable atoms very close to the boundary can be preserved as if it were a closed system, while for two vertically polarizable atoms, the concurrence evolves two times as fast as that in the free space. In the presence of a boundary, entanglement revival is possible for two atoms initially in the symmetric state depending on the orientations of the atomic polarizations, which is in sharp contrast to the fact that the concurrence always decays monotonically in the free space. Interestingly, two initially separable atoms, for which entanglement generation can never happen in the free space with any given acceleration and separation, can get entangled in the presence of a boundary if they are aligned parallel to the boundary. The birth time of entanglement can be noticeably advanced or postponed for the parallel two-atom system placed close to the boundary, while the maximal concurrence during evolution can be significantly enhanced when the atoms are vertically aligned. Moreover, two inertial atoms with different polarizations remain separable all the time, while as the acceleration increases, the delayed birth of entanglement happens, and the nonzero concurrence can be enhanced.

We revisit the concept of turnaround radius in cosmology, in the context of modified gravity. While preliminary analyses were limited to scalar-tensor/$F(R)$ gravity, we extend the definition and the study of this quantity to a much broader class of theories including also quantum $R^2$ gravity. The turnaround radius is computed in terms of the parameters of the theory, and it is shown that a deviation not larger than 10% of this quantity from its value in Einstein’s theory could constrain the model parameters and even rule out some current theories.

We investigate the nature of low $T/W$ dynamical instabilities in various ranges of the stiffness of the equation of state in differentially rotating stars. Here $T$ is the rotational kinetic energy, while $W$ is the gravitational binding energy. We analyze these instabilities in both a linear perturbation analysis and a three-dimensional hydrodynamical simulation. An unstable normal mode of a differentially rotating star is detected by solving an eigenvalue problem along the equatorial plane of the star. The physical mechanism of low $T/W$ dynamical instabilities is also qualitatively confirmed by a scattering of sound waves between corotation and the surface caused by the corotation barrier. Therefore, we can draw a picture of existing pulsation modes unstabilized due to an amplified reflection of sound waves from the corotation barrier. The feature in the eigenfrequency and eigenfunction of the unstable mode in the linear analysis roughly agrees with that in the three-dimensional hydrodynamical simulation in Newtonian gravity. Moreover, the nature of the eigenfunction that oscillates between corotation and the surface for an unstable star requires reinterpretation of pulsation modes in differentially rotating stars. Finally, we propose a manner by which to constrain the stiffness of the equation of state by the direct detection of mode decomposed gravitational waveforms.

The propagation of gravitational waves is explored in the cosmological context. It is explicitly demonstrated that the propagation of gravitational waves could be influenced by the medium. It is shown that in the thermal radiation, the propagation of gravitational waves in general relativity is different from that in the scalar-tensor theory. The propagation of gravitational waves is investigated in the uniform magnetic field. As a result, it is found that cosmic magnetic fields could influence the propagation of gravitational waves to a non-negligible extent. The corresponding estimation for the spiral galaxy NGC 6946 effect is made.

A stochastic gravitational-wave background (SGWB) is expected from the superposition of a wide variety of independent and unresolved astrophysical and cosmological sources from different stages in the evolution of the Universe. Radiometric techniques are used to make sky maps of anisotropies in the SGWB by cross-correlating data from pairs of detectors. The conventional searches can be made hundreds of times faster through the folding mechanism introduced recently. Here we present a newly developed algorithm to perform the SGWB searches in a highly efficient way. Taking advantage of the compactness of the folded data we replaced the loops in the pipeline with matrix multiplications. We also incorporated well-known HEALPix pixelization tools for further standardization and optimization. Our Python-based implementation of the algorithm is available as an open source package PyStoch. Folding and PyStoch together has made the radiometer analysis a few thousand times faster; it is now possible to make all-sky maps of a stochastic background in just a few minutes on an ordinary laptop. Moreover, PyStoch generates a skymap at every frequency bin as an intermediate data product. These techniques have made SGWB searches very convenient and will make computationally challenging analyses like blind all-sky narrowband search feasible.

We explore the constraints on dark sector models imposed by the recent observation of coincident gravitational waves and gamma rays from a binary neutron star merger, GW170817. Rather than focusing on specific models as has been considered by other authors, we explore this in the context of the equation of state approach of which the specific models are special cases. After confirming the strong constraints found by others for Horndeski, Einstein-Aether, and massive gravity models, we discuss how it is possible to construct models which might evade the constraints from GW170817 but still leading to cosmologically interesting modifications to gravity. Possible examples are “miracle cancellations” such as in $f(R)$ models, non-local models and higher-order derivatives. The latter two rely on the dimensionless ratio of the wave number of the observed gravitational waves to the Hubble expansion rate being very large ($\sim {10}^{19}$) which is used to suppress modifications to the speed of gravitational waves.

Measurements of the temperature of the baryons at the end of the cosmic dark ages can potentially set very precise constraints on energy injection from exotic sources, such as annihilation or decay of the dark matter. However, additional effects that lower the gas temperature can substantially weaken the expected constraints on exotic energy injection, whereas additional radiation backgrounds can conceal the effect of an increased gas temperature in measurements of the 21-cm hyperfine transition of neutral hydrogen. Motivated in part by recent claims of a detection of 21-cm absorption from $z\sim 17$ by the EDGES experiment, we derive the constraints on dark matter annihilation and decay that can be placed in the presence of extra radiation backgrounds or effects that modify the gas temperature, such as dark matter (DM)–baryon scattering and early baryon-photon decoupling. We find that if the EDGES observation is confirmed, then constraints on light DM decaying or annihilating to electrons will in most scenarios be stronger than existing state-of-the-art limits from the cosmic microwave background, potentially by several orders of magnitude. More generally, our results allow mapping any future measurement of the global 21-cm signal into constraints on dark matter annihilation and decay, within the broad range of scenarios we consider.

The standard model of particle physics is extended by adding a purely neutrinophilic dark sector. It is shown that theories which accommodate standard model neutrinos as dark radiation are resurrected. Sterile neutrinos bridge the visible and the dark sector and can keep their mutual interactions effective even after the epoch of big bang nucleosynthesis. This prolonged contact between dark matter and standard model neutrinos solves the well-known small-scale structure problems of the cosmological standard model. The dark sector presented in this work satisfies all experimental and observational constraints from particle physics and cosmology.

We investigate the radiative decay of the cosmic neutrino background and its impact on the spectrum of the cosmic microwave background (CMB) that is known to be a nearly perfect black body. We derive exact formulas for the decay of a heavier neutrino into a lighter neutrino and a photon, ${\nu }_j\to {\nu }_i+\gamma$, and of absorption as its inverse, ${\nu }_i+\gamma \to {\nu }_j$, by accounting for the precise form of the neutrino momentum distribution. Our calculations show that if the neutrinos are heavier than $\mathcal{O}(0.1)\mathrm{eV}$ the exact formulas give results that differ by $\sim 50\%$, compared with approximate ones where neutrinos are assumed to be at rest. We also find that spectral distortion due to absorption is more important for heavy neutrino masses (by a factor of $\sim 10$ going from a neutrino mass of 0.01–0.1 eV). By analyzing the CMB spectral data measured with COBE-FIRAS, we obtain lower limits on the neutrino lifetime of ${\tau }_{12}\gtrsim 4\times {10}^{21}\mathrm{s}$ (95% C.L.) for the smaller mass splitting and ${\tau }_{13}\sim {\tau }_{23}\gtrsim {10}^{19}\mathrm{s}$ for the larger mass splitting. These represent up to 1 order of magnitude improvement over previous CMB constraints. With future CMB experiments such as PIXIE, these limits will improve by roughly 4 orders of magnitude. This translates to a projected upper limit on the neutrino magnetic moment (for certain neutrino masses and decay modes) of ${\mu }_{\nu }<3\times {10}^{-11}{\mu }_B$, where ${\mu }_B$ is the Bohr magneton. Such constraints would make future precision CMB measurements competitive with lab-based constraints on neutrino magnetic moments.

The Antarctic Impulsive Transient Antenna, a NASA long-duration balloon payload, searches for radio emission from interactions of ultrahigh-energy neutrinos in polar ice. The third flight of the Antarctic Impulsive Transient Antenna was launched in December 2014 and completed a 22-day flight. We present the results of three analyses searching for Askaryan radio emission of neutrino origin. In the most sensitive of the analyses, we find one event in the signal region on an expected background of $0.7_{-0.3}^{+0.5}$. Though consistent with the background estimate, the event remains compatible with a neutrino hypothesis even after additional postunblinding scrutiny.

For a scalar theory whose classical scale invariance is broken by quantum effects, we compute self-consistent bounce solutions and Green’s functions. Deriving analytic expressions, we find that the latter are similar to the Green’s functions in the archetypal thin-wall model for tunneling between quasidegenerate vacua. The eigenmodes and eigenspectra are, however, very different. Large infrared effects from the modes of low angular momentum $j=0$ and $j=1$, which include the approximate dilatational modes for $j=0$, are dealt with by a resummation of one-loop effects. For a parametric example, this resummation is carried out numerically.

In this work, we study the possibility that dark matter fields transform in the $(1,0)\oplus (0,1)$ representation of the homogeneous Lorentz group. In an effective theory approach, we study the lowest-dimension interacting terms of dark matter with standard model fields, assuming that dark matter fields transform as singlets under the standard model gauge group. There are three dimension-four operators, two of them yielding a Higgs portal to dark matter. The third operator couples the photon and $Z^0$ fields to the higher multipoles of dark matter, yielding a spin portal to dark matter. For low mass dark matter ($D$), the decays $Z^0\to \overline{D}D$ and $H\to \overline{D}D$ are kinematically allowed and contribute to the invisible widths of the $Z^0$ and $H$ bosons. We use experimental results on these invisible widths to constrain the values of the low-energy constants $g_t$ (for the spin portal) and $g_s$, $g_p$ (for the Higgs portal) for this mass region. We calculate the dark matter relic density in our formalism and, using the above constraints, we find that consistency with the experimental value requires dark matter to have a mass $M>43\mathrm{GeV}$ in the case of the spin portal and $M>62\mathrm{GeV}$ for the Higgs portal. For higher mass dark matter ($M>M_H/2$), we calculate the velocity averaged cross section for the annihilation of dark matter into $\overline{b}b$ and ${\tau }^{+}{\tau }^{-}$ and compare with the upper bounds recently reported by Fermi-LAT and DES Collaborations, finding that both portals yield results consistent with the reported upper bounds. Finally, we study direct detection by elastic scattering on nuclei. The Higgs portal yields results consistent with the upper bounds reported recently by the XENON Collaboration. The spin portal can also accommodate this data but requires higher values of the dark matter mass or smaller values of the corresponding coupling.

The full quark-gluon vertex is a crucial ingredient for the dynamical generation of a constituent quark mass from the standard quark gap equation, and its nontransverse part may be determined exactly from the nonlinear Slavnov-Taylor identity that it satisfies. The resulting expression involves not only the quark propagator, but also the ghost dressing function and the quark-ghost kernel, and constitutes the non-abelian extension of the so-called “Ball-Chiu vertex,” known from QED. In the present work we carry out a detailed study of the impact of this vertex on the gap equation and the quark masses generated from it, putting particular emphasis on the contributions directly related with the ghost sector of the theory, and especially the quark-ghost kernel. In particular, we set up and solve the coupled system of six equations that determine the four form factors of the latter kernel and the two typical Dirac structures composing the quark propagator. Due to the incomplete implementation of the multiplicative renormalizability at the level of the gap equation, the correct anomalous dimension of the quark mass is recovered through the inclusion of a certain function, whose ultraviolet behavior is fixed, but its infrared completion is unknown; three particular Ansätze for this function are considered, and their effect on the quark mass and the pion decay constant is explored. The main results of this study indicate that the numerical impact of the quark-ghost kernel is considerable; the transition from a tree-level kernel to the one computed here leads to a 20% increase in the value of the quark mass at the origin. Particularly interesting is the contribution of the fourth Ball-Chiu form factor, which, contrary to the Abelian case, is nonvanishing, and accounts for 10% of the total constituent quark mass.

We present a study of the central exclusive production of the $K^{+}{K}^{-}$ pairs in proton-proton collisions at high energies. We consider diffractive mechanisms including the $K^{+}{K}^{-}$ continuum, the dominant scalar $f_0(980)$, $f_0(1500)$, $f_0(1710)$ and tensor $f_2(1270)$, $f_2^{\prime }(1525)$ resonances decaying into the $K^{+}{K}^{-}$ pairs. We include also photoproduction mechanisms for the nonresonant (Drell-Söding) and the $\varphi (1020)$ resonance contributions. The theoretical results are calculated within the tensor-Pomeron approach including both Pomeron and Reggeon exchanges. Predictions for planned or current experiments at RHIC and LHC are presented. We discuss the influence of the experimental cuts on the integrated cross section and on various differential distributions for outgoing particles. The distributions in two-kaon invariant mass, in a special “glueball filter variable,” as well as examples of angular distributions in the $K^{+}{K}^{-}$ rest frame are presented. We compare the $\varphi (1020)$ and continuum photoproduction contributions to the $f_0(980)$ and continuum diffractive contributions and discuss whether the $\varphi (1020)$ resonance could be extracted experimentally. For the determination of some model parameters we also include a discussion of $K$-nucleon scattering, in particular total cross sections, and of $\varphi (1020)$ photoproduction.

Theoretical predictions for Bhabha scattering observables are presented including complete one-loop electroweak radiative corrections. Longitudinal polarization of the initial beams is taken into account. Numerical results for the asymmetry $A_{LR}$ and the relative correction $\delta$ are given for the set of future $e^{+}{e}^{-}$ collider energies $E_{\mathrm{cm}}=250$, 500, 1000 GeV with various polarization degrees.

We explore the stability of a recently found class of spinning dielectric M2 branes in the 11-dimensional maximally supersymmetric plane-wave background. We find two small windows of instabilities in the dipole ($j=1$) and quadrupole ($j=2$) sector of linear multipole perturbations.

In this paper, we consider the complete momentum-independent quartic order truncation for the effective average action of a real Abelian rank-3 tensorial group field theory. This complete truncation includes nonmelonic as well as double-trace interactions. In the usual functional renormalization group perspective, the inclusion of more operators that belong to the underlying theory space corresponds to an improvement of the truncation of the effective average action. We show that the inclusion of nonmelonic and double-trace operators in the truncation brings subtleties. In particular, we discuss the assignment of scaling dimensions to the nonmelonic sector and how the inclusion of double-trace operators considerably changes the results for critical exponents with respect to those obtained when they are not included. We argue that this is not a particular problem of the present model by comparing the results with a pure tensor model. We discuss how these issues should be investigated in future work.