Fermion production in an external Coulomb field on a de Sitter expanding universe is studied. The amplitude and probability of pair production in an external Coulomb field are computed and the cases of large/small values of the expansion factor comparatively with the particle mass are studied. We obtain from our calculations that the modulus of the momentum is no longer a conserved quantity. We find that in the de Sitter space there are probabilities for production processes where the helicity is no longer conserved. For a vanishing expansion factor, we recover the Minkowski limit where the amplitude of this process vanishes. The rate of pair production in a Coulomb field is found to be important in the early Universe when the expansion factor was large comparatively with the particle mass.

We discuss combined constraints, coming from the cosmic microwave background shift parameter $\mathcal{R}$, the baryon acoustic oscillations distance parameter $\mathcal{A}$, and from the latest type Ia supernovae data, imposed on cosmological models which allow sudden future singularities of pressure. We show that due to their weakness such sudden singularities may happen in the very near future and that at present they can mimic standard dark energy models.

The bizarre behavior of the apparent (black hole and cosmological) horizons of the McVittie spacetime is discussed using, as an analogy, the Schwarzschild-de Sitter-Kottler spacetime (which is a special case of McVittie anyway). For a dust-dominated “background” universe, a black hole cannot exist at early times because its (apparent) horizon would be larger than the cosmological (apparent) horizon. A phantom-dominated background universe causes this situation, and the horizon behavior, to be time-reversed.

Coalescences of binary neutron stars and/or black holes are amongst the most likely gravitational-wave signals to be observed in ground-based interferometric detectors. Apart from the astrophysical importance of their detection, they will also provide us with our very first empirical access to the genuine strong-field dynamics of general relativity (GR). We present a new framework based on Bayesian model selection aimed at detecting deviations from GR, subject to the constraints of the Advanced Virgo and LIGO detectors. The method tests the consistency of coefficients appearing in the waveform with the predictions made by GR, without relying on any specific alternative theory of gravity. The framework is suitable for low signal-to-noise ratio events through the construction of multiple subtests, most of which involve only a limited number of coefficients. It also naturally allows for the combination of information from multiple sources to increase one’s confidence in GR or a violation thereof. We expect it to be capable of finding a wide range of possible deviations from GR, including ones which, in principle, cannot be accommodated by the model waveforms, on the condition that the induced change in phase at frequencies where the detectors are the most sensitive is comparable to the effect of a few percent change in one or more of the low-order post-Newtonian phase coefficients. In principle, the framework can be used with any GR waveform approximant, with arbitrary parametrized deformations, to serve as model waveforms. In order to illustrate the workings of the method, we perform a range of numerical experiments in which simulated gravitational waves modeled in the restricted post-Newtonian, stationary phase approximation are added to Gaussian and stationary noise that follows the expected Advanced LIGO/Virgo noise curves.

For a reliable prediction of the NMSSM Higgs boson signatures at present and future high-energy colliders and a proper distinction of the NMSSM and MSSM Higgs sector the precise knowledge of the Higgs boson masses including higher-order corrections is indispensable. In this paper, the one-loop corrections to the neutral NMSSM Higgs boson masses and mixings are calculated in three different renormalization schemes. In addition to the $\overline{\mathrm{DR}}$ renormalization scheme, existing in the literature, two other schemes are adopted. Furthermore, the dependence on the value of the top quark mass is investigated. From this and the variation of the renormalization scale, at one-loop level, the residual theory error due to missing higher-order corrections can be estimated to be of the order of 10%.

Recently it was claimed that QCD condensates were associated with the internal dynamics of the hadrons. We challenge this “in-hadron” picture of the QCD condensates and show that it conflicts with well established concepts and experimental facts for the example of the quark condensate. We explicitly demonstrate the vacuum nature of the quark condensate by a model calculation.

In a series of papers, it has been shown that the distribution of polarization position angles for visible light from quasars is not random in extremely large regions of the sky. As explained in a recent article, the measurement of vanishing circular polarization for such quasars is an important problem for a mechanism involving the mixing with axionlike particles in external magnetic fields. In this paper, we stress that a recent report of similar coherent orientations of polarization in radio waves further disfavors the need for such particles, as an effect at these wavelengths would be extremely suppressed or would directly contradict data.

The open string tachyon and $U(1)$ gauge field as longitudinal fluctuations and the velocity as a transverse fluctuation of an arbitrary dimensional $D$-brane are considered as boundary deformations of a closed superstring free action. The path integral approach will be applied to calculate the corresponding generalized boundary states using supersymmetrized boundary actions. Obtaining the disk partition functions from the boundary states and studying the effect of tachyon condensation on both of them in the Neveu-Schwarz-Neveu-Schwarz and Ramond-Ramond sectors, leads to results that differ from the established ones.

Three-dimensional fluids with nontrivial vorticity can be described holographically. It is well known that the Kerr-AdS geometry gives rise to a cyclonic flow. Here we note that Taub-NUT-${\mathrm{AdS}}_4$ geometries give rise to a rotating fluid with vortex flow. The Randers and Zermelo forms of the boundary metrics provide alternative descriptions of the fluid by inertial comoving or by accelerated observers. Such fluids possess acoustic horizons. Moreover, light propagation on the boundary Taub-NUT fluid will encounter an optical horizon associated with closed timelike curves. In the latter case the Misner string introduces a multi-valuedness of the scalar fluctuations which can be attributed to the anyonic nature of the boundary vortex.

In a recent paper, Harlow, Maltz, and Witten showed that a particular proposal for the timelike Liouville three-point function, originally due to Zamolodchikov and to Kostov and Petkova, can actually be computed by the original Liouville path integral evaluated on a new integration cycle. Here, we discuss a Coulomb gas computation of the timelike three-point function and show that an analytic extension of the Selberg-type integral formulas involved reproduces the same expression, including the adequate normalization. A notable difference with the spacelike calculation is pointed out.

It is well known that integrable charges for short-range (e.g. nearest-neighbor) spin chains with periodic boundary conditions can be recursively generated by a so-called boost operator. In the past, this iterative construction has been generalized to periodic long-range spin chains as they appear in the context of the gauge/gravity correspondence. Here we introduce recursion relations for open long-range spin chain charges converting a short-range into a long-range integrable model.

The aim of this paper is to report on the existence of a wide variety of exact solutions, ranging from black holes to wormholes, when a conformally coupled scalar field with a self-interacting potential containing a linear, a cubic and a quartic self interaction is taken as a source of the energy-momentum tensor, in the Einstein theory with a cosmological constant. Among all the solutions there are two particularly interesting. On the one hand, the spherically symmetric black holes when the cosmological constant is positive; they are shown to be everywhere regular, namely, there is no singularity neither inside nor outside the event horizon. On the other hand, there are spherically symmetric and topological wormholes that connect two asymptotically (anti) de Sitter regions with a different value for the cosmological constant. The regular black holes and the wormholes are supported by everywhere regular scalar field configurations.

In this paper we apply the five-dimensional $f(T)$ gravity with $f(T)=T+k{T}^n$ to brane scenario to explore the solutions under a given warp factor, and we find that the analytic domain wall solution will be a double-kink solution when the geometric effect of spacetime torsion is strongly enhanced. We also investigate the localization of fermion fields on the split branes corresponding to the double-kink solution.

We consider a possibility of identification of sources of cosmic rays (CR) of the energy above 1 TeV via observation of degree-scale extended $\gamma$-ray emission which traces the locations of recent sources in the Galaxy. Such emission in the energy band above 100 GeV is produced by CR nuclei and electrons released by the sources and spreading into the interstellar medium. We use the data from the Fermi $\gamma$-ray telescope to locate the degree-scale 100 GeV $\gamma$-ray sources. We find that the number of such sources and their overall power match to those expected when CRs injection events happen every $\sim 100\mathrm{yr}$ in portions of $\sim {10}^{50}\mathrm{erg}$. We find that most of the sources are associated to pulsars with spin-down age less than $\sim 30\mathrm{kyr}$ and hence to the recent supernova explosions. This supports the hypothesis of supernova origin of Galactic CRs. We notice that the degree-scale extended emission does not surround shell-like supernova remnants without pulsars. Based on this observation, we argue that the presence of the pulsar is essential for the CR acceleration process. We expect that a significant fraction of the degree-scale sources should be detectable as extended sources with ${\mathrm{km}}^3$-scale neutrino detectors.

We analyze restrictions on the stochastic superspace parameter space arising from $1{\mathrm{fb}}^{-1}$ of LHC data, and bounds on sparticle masses, cold dark matter relic density, and the branching ratio of the process $B_s\to {\mu }^{+}{\mu }^{-}$. A region of parameter space consistent with these limits is found where the stochasticity parameter, $\xi$, takes values in the range $-2200\mathrm{GeV}<\xi <-900\mathrm{GeV}$, provided the cutoff scale is $\mathcal{O}({10}^{18})\mathrm{GeV}$.

We present a fit to precision electroweak data in the standard model (SM) extended by an additional vector boson, $Z^{\prime }$, with suppressed couplings to the electron compared to the $Z$ boson, with couplings to the $b$-quark, and with mass close to the mass of the $Z$ boson. This scenario provides an excellent fit to forward-backward asymmetry of the $b$-quark measured on the $Z$-pole and $\pm 2\mathrm{GeV}$ off the $Z$-pole, and to lepton asymmetry, $A_e$, obtained from the measurement of left-right asymmetry for hadronic final states, and thus it removes the tension in the determination of the weak mixing angle from these two measurements. It also leads to a significant improvement in the total hadronic cross-section on the $Z$-pole and $R_b$ measured at energies above the $Z$-pole. We explore in detail properties of the $Z^{\prime }$ needed to explain the data and present a model for $Z^{\prime }$ with required couplings. The model preserves standard model Yukawa couplings; it is anomaly-free and can be embedded into grand unified theories. It allows a choice of parameters that does not generate any flavor violating couplings of the $Z^{\prime }$ to standard model fermions. Out of standard model couplings, it only negligibly modifies the left-handed bottom quark coupling to the $Z$ boson and the third column of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix. Modifications of standard model couplings in the charged lepton sector are also negligible. It predicts an additional down-type quark, $D$, with mass in the few hundred GeV range, and an extra lepton doublet, $L$, possibly much heavier than the $D$-quark. We discuss signatures of the $Z^{\prime }$ at the Large Hadron Collider and calculate the $Z^{\prime }b$ production cross-section, which is the dominant production mechanism for the $Z^{\prime }$.

We present a new global QCD analysis of nuclear parton distribution functions and their uncertainties. In addition to the most commonly analyzed data sets for the deep-inelastic scattering of charged leptons off nuclei and Drell-Yan dilepton production, we include also measurements for neutrino-nucleus scattering and inclusive pion production in deuteron-gold collisions. The analysis is performed at next-to-leading order accuracy in perturbative QCD in a general mass variable flavor number scheme, adopting a current set of free nucleon parton distribution functions, defined accordingly, as reference. The emerging picture is one of consistency, where universal nuclear modification factors for each parton flavor reproduce the main features of all data without any significant tension among the different sets. We use the Hessian method to estimate the uncertainties of the obtained nuclear modification factors and examine critically their range of validity in view of the sparse kinematic coverage of the present data. We briefly present several applications of our nuclear parton densities in hard nuclear reactions at BNL-RHIC, CERN-LHC, and a future electron-ion collider.

The energy loss parameter $\widehat{q}$ is one of the fundamental transport parameters of hadronic matter. Using the twist-4 collinear approach, we show that the $\cos \varphi$ azimuthal asymmetry in unpolarized semi-inclusive deeply inelastic scattering off a large nucleus at intermediate transverse momentum is a sensitive observable for its determination. The effect is due to the suppression of the azimuthal asymmetry by final-state multiple scattering.

We investigate the direct and indirect bounds on dipole operators involving the top quark. A careful analysis shows that the experimental upper limit on the neutron electric dipole moment strongly constrains the chromo-electric dipole of the top. We improve previous bounds by 2 orders of magnitude. This has significant implications for new physics models and it also means that $CP$ violation in top pair production mediated by dipole operators will not be accessible at the LHC. The $CP$ conserving chromo-magnetic dipole moments are constrained by recent measurements of the $t\overline{t}$ spectrum by the ATLAS collaboration. We also update the indirect constraints on electric and magnetic dipole moments from radiative $b\to s$ transitions, finding that they can be considerably larger than their colored counterparts.

In this paper, we consider an extension to Eddington’s proposal for the gravitational action. We study tensor perturbations of a homogeneous and isotropic space-time in the Eddington regime, where modifications to Einstein gravity are strong. We find that the tensor mode is linearly unstable deep in the Eddington regime and discuss its cosmological implications.