Observations of the INTEGRAL satellite revealed the presence of yet unexplained excess in the central region of the Galaxy at energies around 511 keV. These gamma rays are produced in the process of positron annihilation; the needed rate is around $10^{42}{\mathrm{s}}^{-1}$. In this short paper it is shown that ${\beta }^{+}$ -emitting isotopes that are formed in interactions of subrelativistic cosmic rays with light nuclei (CNONe) can account for a considerable fraction—up to several tens of percent—of $e^{+}$ production rate in the central region.

Using a bottom up phenomenological approach we constructed a simple doubly charged vector lepton $E^{\pm \pm }$ model for the possible 750 GeV diphoton resonance $\mathrm{\Phi }$ at the LHC assuming it to be a scalar particle. Since no stable doubly charged leptons are seen, to facilitate their decays we complete the model by adding a charged standard model (SM) electroweak scalar $S^{\pm }$. $\mathrm{\Phi }$ is a SM singlet and can be either an inert scalar or a Higgs field. In the inert case more than one vector lepton is required to account for the photon fusion production of the resonance if the model is to remain perturbative. For a Higgs boson case $S^{\pm }$ can assist the production mechanism without using more than one such lepton. We also found that precision measurements constrain the couplings of $E^{\pm \pm }$ and $S^{\pm }$ to SM particles to be small. This raises the possibility that they can be fairly long lived and can give rise to displaced vertices if produced at the LHC.

We explore a model based on the classically scale-invariant standard model (SM) with a strongly coupled vectorlike dynamics, which is called hypercolor (HC). The scale symmetry is dynamically broken by the vectorlike condensation at the TeV scale, so that the SM Higgs acquires the negative mass squared by the bosonic seesaw mechanism to realize the electroweak symmetry breaking. An elementary pseudoscalar $S$ is introduced to give masses for the composite Nambu-Goldstone bosons (HC pions): The HC pion can be a good target to explore through a diphoton channel at the LHC. As a consequence of the bosonic seesaw, the fluctuating mode of $S$, which we call $s$, develops tiny couplings to the SM particles and is predicted to be very light. The $s$ predominantly decays to a diphoton and can behave as invisible axionlike dark matter. The mass of the $s$ dark matter is constrained by currently available cosmological and astrophysical limits to be ${10}^{-4}\mathrm{eV}\lesssim m_s\lesssim 1\mathrm{eV}$. We find that a sufficient amount of relic abundance for the $s$ dark matter can be accumulated via the coherent oscillation. The detection potential in microwave cavity experiments is also addressed.

We report new results on the conformal properties of an important strongly coupled gauge theory, a building block of composite Higgs models beyond the Standard Model. With twelve massless fermions in the fundamental representation of the SU(3) color gauge group, an infrared fixed point (IRFP) of the $\beta$-function was recently reported in the theory [A. Cheng, A. Hasenfratz, Y. Liu, G. Petropoulos, and D. Schaich, J. High Energy Phys. 05 (2014) 137] with uncertainty in the location of the critical gauge coupling inside the narrow $[6.0<g_{*}^2<6.4]$ interval and widely accepted since as the strongest evidence for a conformal fixed point and scale invariance in the theory with model-building implications. Using the exact same renormalization scheme as the previous study, we show that no fixed point of the $\beta$-function exists in the reported interval. Our findings eliminate the only seemingly credible evidence for conformal fixed point and scale invariance in the $N_f=12$ model whose infrared properties remain unresolved. The implications of the recently completed 5-loop QCD $\beta$-function for arbitrary flavor number are discussed with respect to our work.

We implement the effects of disorder on a holographic superconductor by introducing a random chemical potential on the boundary. We demonstrate explicitly that increasing disorder leads to the formation of islands where the superconducting order is enhanced and subsequently to the transition to a metal. We study the behavior of the superfluid density and of the conductivity as a function of the strength of disorder. We find explanations for various marked features in the conductivities in terms of hydrodynamic quasinormal modes of the holographic superconductors. These identifications plus a particular disorder-dependent spectral weight shift in the conductivity point to a signature of the Higgs mode in the context of disordered holographic superconductors. We observe that the behavior of the order parameter close to the transition is not mean-field type as in the clean case; rather we find robust agreement with $\exp (-A|T-T_c{|}^{-\nu })$, with $\nu =1.03\pm 0.02$ for this disorder-driven smeared transition.

The purpose of this paper is to calculate the Pomeron intercepts from the BFKL equation with the running coupling constant and the gluon mass generated by the Higgs-like mechanism, and to estimate the influence of the infrared dynamics on the spectrum. We found that as in the massless case, the spectrum of positive Regge singularities is discrete and the leading Pomeron has a considerable dependence on nonperturbative effects. We cross-checked this result with finite element analysis, semiclassical approximation and variational methods and confirmed the infrared sensitivity of the leading Pomeron. This fact is related to the infrared instability of the BFKL equation in QCD, with a running coupling. The subleading poles have a mild sensitivity to the soft physics, and are well described by known semiclassical methods. Also for the first time we study the BFKL equation for the various running coupling prescriptions suggested in the literature.

The cross section of the process $e^{+}{e}^{-}\to \omega \eta$ is measured in the center-of-mass energy range 1.34–2.00 GeV. The analysis is based on data collected with the SND detector at the VEPP-2000 $e^{+}{e}^{-}$ collider. The measured $e^{+}{e}^{-}\to \omega \eta$ cross section is the most accurate to date. A significant discrepancy is observed between our data and previous BABAR measurements.

Motivated by statements in the literature which contradict two general theorems, the static and spherically symmetric Brans solutions of scalar-tensor gravity are analyzed explicitly in both the Jordan and the Einstein conformal frames. Depending on the parameter range, these solutions describe wormholes or naked singularities but not black holes.

Second-order self-force computations, which will be essential in modeling extreme-mass-ratio inspirals, involve two major new difficulties that were not present at first order. One is the problem of large scales, discussed in Pound [Phys. Rev. D 92, 104047 (2015)]. Here we discuss the second difficulty, which occurs instead on small scales: if we expand the field equations in spherical harmonics, then because the first-order field contains a singularity, we require an arbitrarily large number of first-order modes to accurately compute even a single second-order mode. This is a generic feature of nonlinear field equations containing singularities, allowing us to study it in the simple context of a scalar toy model in flat space. Using that model, we illustrate the problem and demonstrate a robust strategy for overcoming it.

We introduce a new resummed analytical form of the post-Newtonian (PN), factorized, multipolar amplitude corrections $f_{\ell m}$ of the effective-one-body (EOB) gravitational waveform of spinning, nonprecessing, circularized, coalescing black hole binaries (BBHs). This stems from the following two-step paradigm: (i) the factorization of the orbital (spin-independent) terms in $f_{\ell m}$; (ii) the resummation of the residual spin (or orbital) factors. We find that resumming the residual spin factor by taking its inverse resummed (iResum) is an efficient way to obtain amplitudes that are more accurate in the strong-field, fast-velocity regime. The performance of the method is illustrated on the $\ell =2$ and $m=(1,2)$ waveform multipoles, both for a test mass orbiting around a Kerr black hole and for comparable-mass BBHs. In the first case, the iResum $f_{\ell m}$’s are much closer to the corresponding “exact” functions (obtained by numerically solving the Teukolsky equation) up to the light ring than the nonresummed ones, especially when the black-hole spin is nearly extremal. The iResum paradigm is also more efficient than including higher post-Newtonian terms (up to 20PN order): the resummed 5PN information yields per se a rather good numerical or analytical agreement at the last stable orbit and a well-controlled behavior up to the light ring. For comparable mass binaries (including the highest PN-order information available, 3.5PN), comparing EOB with numerical relativity (NR) data shows that the EOB/NR fractional disagreement at merger, without NR calibration of the EOB waveform, is generically reduced by iResum, from 40% of the usual approach to just a few percent. This suggests that EOBNR waveform models for coalescing BBHs may be improved by using iResum amplitudes.

During the last few decades, there has been a growing interest in exact solutions of Einstein equations describing razor-thin disks. Despite the progress in this area, the analytical study of geodesic motion crossing the disk plane in these systems has not yet been well developed. In the present work, we propose a definite vertical stability criterion for circular equatorial timelike geodesics in static, axially symmetric thin disks, possibly surrounded by other structures preserving axial symmetry. It turns out that the strong energy condition for the disk stress-energy content is sufficient for the vertical stability of these orbits. Moreover, adiabatic invariance of the vertical action variable gives us an approximate third integral of motion for oblique orbits that deviate slightly from the equatorial plane. This new approximate third integral certainly points to a better understanding of the analytical properties of these orbits. The results presented here, derived for static spacetimes, may be a starting point to study the motion around rotating, stationary razor-thin disks. Our results also allow us to conjecture that the strong energy condition should be sufficient to assure transversal stability of periodic orbits for any singular timelike hypersurface, provided it is invariant under the geodesic flow.

A novel approach to the effective-one-body description of gravitationally interacting two-body systems is introduced. This approach is based on the post-Minkowskian approximation scheme (perturbation theory in $G$, without assuming small velocities) and employs a new dictionary focussing on the functional dependence of the scattering angle on the total energy and the total angular momentum of the system. Using this approach, we prove to all orders in $v/c$ two results that were previously known to hold only to a limited post-Newtonian accuracy: (i) the relativistic gravitational dynamics of a two-body system is equivalent, at first post-Minkowskian order, to the relativistic dynamics of an effective test particle moving in a Schwarzschild metric, and (ii) this equivalence requires the existence of an exactly quadratic map between the real (relativistic) two-body energy and the (relativistic) energy of the effective particle. The same energy map is also shown to apply to the effective-one-body description of two masses interacting via tensor-scalar gravity.

Phenomenological functions $\mathrm{\Sigma }$ and $\mu$ (also known as $G_{\text{light}}/G$ and $G_{\text{matter}}/G$) are commonly used to parametrize possible modifications of the Poisson equation relating the matter density contrast to the lensing and the Newtonian potentials, respectively. They will be well constrained by future surveys of large-scale structure. But what would the implications of measuring particular values of these functions be for modified gravity theories? We ask this question in the context of the general Horndeski class of single-field scalar-tensor theories with second-order equations of motion. We find several consistency conditions that make it possible to rule out broad classes of theories based on measurements of $\mathrm{\Sigma }$ and $\mu$ that are independent of their parametric forms. For instance, a measurement of $\mathrm{\Sigma }\ne 1$ would rule out all models with a canonical form of kinetic energy, while finding $\mathrm{\Sigma }-1$ and $\mu -1$ to be of opposite sign would strongly disfavor the entire class of Horndeski models. We separately examine the large- and the small-scale limits, the possibility of scale dependence, and the consistency with bounds on the speed of gravitational waves. We identify subclasses of Horndeski theories that can be ruled out based on the measured difference between $\mathrm{\Sigma }$ and $\mu$.

We study the spherically symmetric gravitational collapse of massless scalar matter field in asymptotic flat spacetime in the Starobinsky $R^2$ gravity, one specific model in the $f(R)$ gravity. In the Einstein frame of $f(R)$ gravity, an additional scalar field arises due to the conformal transformation. We find that in addition to the usual competition between gravitational energy and kinetic energy in the process of gravitational collapse, the new scalar field brought by the conformal transformation adds one more competing force in the dynamical system. The dynamical competition can be controlled by tuning the amplitudes of the initial perturbations of the new scalar field and the matter field. To understand the physical reasons behind these phenomena, we analyze the gravitational potential behavior and calculate the Ricci scalar at center with the change of initial amplitudes of perturbations. We find rich physics on the formation of black holes through gravitational collapse in $f(R)$ gravity.

Using numerical simulations, we study the accretion of a phantom scalar field into a black hole and track the black-hole-horizon shrinking process. We integrate the amount of field left outside the black hole during the process in terms of the properties of the wave packet sent toward the black hole. Our results indicate that the accretion of thick wave packets with small wave number is inefficient and a portion of the scalar field remains outside the black hole.

In this paper, we study some properties of what is called the oscillaton, a spherically symmetric object made of a real time-dependent scalar field. Using an exponential scalar potential instead of a quadratic one discussed in previous works, as a new choice, we investigate the oscillaton properties with this potential. Solving the differential equation system resulting from the Einstein-Klein-Gordon equations reveals the importance of the oscillatons as candidates for dark matter. Meanwhile, a simplification called the stationary limit procedure is also carried out.

In this work, we present a method for implementing the $\delta N$ formalism to study the primordial non-Gaussianity produced in multiple three-form field inflation. Using a dual description relating three-form fields to noncanonical scalar fields, and employing existing results, we produce expressions for the bispectrum of the curvature perturbation in terms of three-form quantities. We study the bispectrum generated in a two three-form field inflationary scenario for a particular potential that for suitable values of the parameters was found in earlier work to give values of the spectral index and ratio of tensor to scalar perturbations compatible with current bounds. We calculate the reduced bispectrum for this model, finding an amplitude in equilateral and orthogonal configurations of $\mathcal{O}(1)$ and in the squeezed limit of $\mathcal{O}({10}^{-3})$. We confirm, therefore, that this three-form inflationary scenario is compatible with present observational constraints.

A phase transition to quark matter can lead to interesting phenomenological consequences in core-collapse supernovae, e.g., triggering an explosion in spherically symmetric models. However, until now, this explosion mechanism was only shown to be working for equations of state that are in contradiction with recent pulsar mass measurements. Here, we identify that this explosion mechanism is related to the existence of a third family of compact stars. For the equations of state investigated, the third family is only pronounced in the hot, early stages of the protocompact star and absent or negligibly small at zero temperature and thus represents a novel kind of third family. This interesting behavior is a result of unusual thermal properties induced by the phase transition, e.g., characterized by a decrease of temperature with increasing density for isentropes, and can be related to a negative slope of the phase transition line in the temperature-pressure phase diagram.

In this paper, we explore the dynamical chiral symmetry breaking by employing a two-flavor Nambu–Jona-Lasinio (NJL) model with constant external magnetic field. After changing the coupling strength of the NJL model, we found that the Wigner-Weyl solution and Nambu-Goldstone solution of the gap equation could coexist. Even though the gap equation only has Nambu-Goldstone solution at zero temperature, the Wigner-Weyl solution may appear when magnetic field strength and temperature are nonzero. For the Nambu-Goldstone solution, magnetic field and temperature have opposite impact on the chiral dynamical mass. In the chiral limit, the magnetic field dependence of chiral dynamical mass reveals the existence of inverse magnetic catalysis for the Wigner-Weyl solution. However, the two phases have different responses to the magnetic field and temperature in the chiral limit but the same beyond chiral limit. Furthermore, the order of the transition from the Nambu-Goldstone phase to Wigner-Weyl phase depends on the choice of model parameters. We have also calculated the susceptibilities of dynamical mass with respect to the temperature.