The main objective of this comment is to correct the density number of created fermions by an electric field in the () dimensional de Sitter space-time communicated by V. M. Villalba in []. This comment will show how the positive and negative energy solutions are connected to one another by the charge conjugation. Some concluding remarks are made.

In this paper, a Bañados-Teitelboim-Zanelli (BTZ) black hole [Phys. Rev. Lett. 69, 1849 (1992)] is constructed from an exact solution of the Einstein field equations in a ($2+1$)—dimensional anti—de Sitter spacetime in the context of noncommutative geometry. The BTZ black hole turns out to have either two horizons, no horizon, or a single horizon corresponding to a minimal mass. Certain thermodynamical properties are investigated, including Hawking temperature, entropy, and heat capacity. Also discussed is the geodesic structure of BTZ black holes for both massless and massive particles. In particular, it is shown that bound orbits for test particles are possible.

We study the dynamical evolution of the gravitational-wave driven instability of the $f$ mode in rapidly rotating relativistic stars. With an approach based on linear perturbation theory we describe the evolution of the mode amplitude and follow the trajectory of a newborn neutron star through its instability window. The influence on the $f$-mode instability of the magnetic field and the presence of an unstable $r$ mode is also considered. Two different configurations are studied in more detail, an $N=1$ polytrope with a typical mass and radius and a more massive polytropic $N=0.62$ model with gravitational mass $M=1.98M_{\odot }$. We study several evolutions with different initial rotation rates and temperature and determine the gravitational waves radiated during the instability. In more massive models, an unstable $f$ mode with a saturation energy of about ${10}^{-6}{M}_{\odot }{c}^2$ may generate a gravitational wave signal which can be detected by the Advanced LIGO/Virgo detector from the Virgo cluster. The magnetic field affects the evolution and then the detectability of the gravitational radiation when its strength is higher than ${10}^{12}\mathrm{G}$, while the effects of an unstable $r$ mode become dominant when this mode reaches the maximum saturation value allowed by nonlinear mode couplings. However, the relative saturation amplitude of the $f$ and $r$ modes must be known more accurately in order to provide a definitive answer to this issue. From the thermal evolution we find also that the heat generated by shear viscosity during the saturation phase completely balances the neutrinos’ cooling and prevents the star from entering the regime of mutual friction. The evolution time of the instability is therefore longer and the star loses significantly larger amounts of angular momentum via gravitational waves.

It is well-known that the standard Britto-Cachazo-Feng-Witten construction cannot be used for on-shell amplitudes in effective field theories due to bad behavior for large shifts. We show how to solve this problem in the case of the $SU(N)$ nonlinear sigma model, i.e., nonrenormalizable model with an infinite number of interaction vertices, using scaling properties of the semi-on-shell currents, and we present new on-shell recursion relations for all on-shell tree-level amplitudes in this theory.

We present a detailed description of the $Q^2$ and $x$ dependence of the structure functions $F_2$ and $F_L$ as extracted from the deep inelastic scattering data at HERA in the small Bjorken $x$ region. Making use of a collinearly improved Balitsky-Fadin-Kuraev-Lipatov equation at next-to-leading order and a treatment of the running of the coupling using non-Abelian physical renormalization together with the Brodsky-Lepage-Mackenzie scale choice allows us to reach low values of $Q^2$. We also provide some predictions for future lepton-hadron colliders.

In this paper we derive holographic wave equations for hadrons with arbitrary spin starting from an effective action in a higher-dimensional space asymptotic to anti–de Sitter (AdS) space. Our procedure takes advantage of the local tangent frame, and it applies to all spins, including half-integer spins. An essential element is the mapping of the higher-dimensional equations of motion to the light-front Hamiltonian, thus allowing a clear distinction between the kinematical and dynamical aspects of the holographic approach to hadron physics. Accordingly, the nontrivial geometry of pure AdS space encodes the kinematics, and the additional deformations of AdS space encode the dynamics, including confinement. It thus becomes possible to identify the features of holographic QCD, which are independent of the specific mechanisms of conformal symmetry breaking. In particular, we account for some aspects of the striking similarities and differences observed in the systematics of the meson and baryon spectra.

At hadron colliders invisible particles $\chi$ can be inferred only through observation of the transverse component of the vectorial sum of their momenta—missing $E_T$ or missing transverse energy (MET)—preventing reconstruction of the masses of their mother particles. Here we outline situations where prior prejudice about the event kinematics allows one to make the most of MET by decomposing it into its expected sum of transverse contributions, each of which may be promoted to a full four-momentum approximating the associated $\chi$. Such prejudice arises when all $\chi$ in the event are expected to be light and (anti-)parallel to a visible object, due to spin correlations, back-to-back decays or boosted decays. We focus on the last of these, with boosted semi-invisibly decaying neutralinos widely motivated in supersymmetry (in the presence of light gravitinos, singlinos, photini or pseudo-Goldstini), and demonstrate our simple method’s ability to reconstruct sharp mass peaks from the MET decomposition.

We report on a search for $B_s^0\to {\mu }^{+}{\mu }^{-}$ and $B^0\to {\mu }^{+}{\mu }^{-}$ decays using proton-antiproton collision data at $\sqrt{s}=1.96\mathrm{TeV}$ corresponding to $10{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. The observed number of $B^0$ candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of $\mathcal{B}(B^0\to {\mu }^{+}{\mu }^{-})<4.6\times {10}^{-9}$ at 95% confidence level. We observe an excess of $B_s^0$ candidates. The probability that the background processes alone could produce such an excess or larger is 0.94%. The probability that the combination of background and the expected standard model rate of $B_s^0\to {\mu }^{+}{\mu }^{-}$ could produce such an excess or larger is 6.8%. These data are used to determine a branching fraction $\mathcal{B}(B_s^0\to {\mu }^{+}{\mu }^{-})=({1.3}_{-0.7}^{+0.9})\times {10}^{-8}$ and provide an upper limit of $\mathcal{B}(B_s^0\to {\mu }^{+}{\mu }^{-})<3.1\times {10}^{-8}$ at 95% confidence level.

In this work we study thermal leptogenesis using nonequilibrium quantum field theory. Starting from fundamental equations for correlators of the quantum fields we describe the steps necessary to obtain quantum-kinetic equations for quasiparticles. These can easily be compared to conventional results and overcome conceptional problems inherent in the canonical approach. Beyond $CP$-violating decays we include also those scattering processes which are tightly related to the decays in a consistent approximation of fourth order in the Yukawa couplings. It is demonstrated explicitly how the $S$-matrix elements for the scattering processes in the conventional approach are related to two- and three-loop contributions to the effective action. We derive effective decay and scattering amplitudes taking medium corrections and thermal masses into account. In this context we also investigate $CP$-violating Higgs decay within the same formalism. From the kinetic equations we derive rate equations for the lepton asymmetry improved in that they include quantum-statistical effects and medium corrections to the quasiparticle properties.

The symmetries of a scalar field theory in multifractional spacetimes are analyzed. The free theory realizes the Poincaré algebra, and the associated symmetries are modifications of ordinary translations and Lorentz transformations. In the interacting case, the Poincaré algebra is broken by interaction terms. The Feynman propagator of the scalar field is computed and found to possess the usual mass poles. As a consequence of these findings, the mass of a particle is a well-defined concept at all scales, and a perturbative quantum theory can be constructed.

In this paper, we investigate the thermodynamics of Lifshitz black branes in the presence of a nonlinear massless electromagnetic field. We begin by introducing the appropriate action in grand-canonical and canonical ensembles for a nonlinear electromagnetic field. The condition on the parameters of the metric for having black brane solutions will be presented. Since the field equations cannot be solved for an arbitrary value of the critical exponent $z$, we obtain a conserved quantity along the $r$ coordinate that enables us to relate the parameters of the metric at the horizon and at infinity. Then, we calculate the energy density of the Lifshitz black brane through the use of the counterterm method generalized for the asymptotic Lifshitz spacetimes. Finally, we present a relation between the energy density and the thermodynamical quantities, electric potential, charge density, temperature, and entropy density. This relation is the generalization of the Smarr formula for anti–de Sitter black branes.

Bound geodesic orbits around a Kerr black hole can be parametrized by three constants of the motion: the (specific) orbital energy, angular momentum, and Carter constant. Generically, each orbit also has associated with it three frequencies, related to the radial, longitudinal, and (mean) azimuthal motions. Here, we note the curious fact that these two ways of characterizing bound geodesics are not in a one-to-one correspondence. While the former uniquely specifies an orbit up to initial conditions, the latter does not: there is a (strong-field) region of the parameter space in which pairs of physically distinct orbits can have the same three frequencies. In each such isofrequency pair, the two orbits exhibit the same rate of periastron precession and the same rate of Lense-Thirring precession of the orbital plane, and (in a certain sense) they remain “synchronized” in phase.

Inspired by “quantum graphity” models for spacetime, a statistical model of graphs is proposed to explore possible realizations of emergent manifolds. Graphs with given numbers of vertices and edges are considered, governed by a very general Hamiltonian that merely favors graphs with near-constant valency and local rotational symmetry. The ratio of vertices to edges controls the dimensionality of the emergent manifold. The model is simulated numerically in the canonical ensemble for a given vertex to edge ratio, where it is found that the low-energy states are almost triangulations of two-dimensional manifolds. The resulting manifold shows topological “handles” and surface intersections in a higher embedding space, as well as nontrivial fractal dimension consistent with previous spectral analysis, and nonlocal links consistent with models of disordered locality. The transition to an emergent manifold is first order, and thus dependent on microscopic structure. Issues involved in interpreting nearly fixed valency graphs as Feynman diagrams dual to a triangulated manifold as in matrix models are discussed. Another interesting phenomenon is that the entropy of the graphs are superextensive, a fact known since Erdős, which results in a transition temperature of zero in the limit of infinite system size: infinite manifolds are always disordered. Aside from a finite universe or diverging coupling constraints as possible solutions to this problem, long-range interactions between vertex defects also resolve the problem and restore a nonzero transition temperature, in a manner similar to that in low-dimensional condensed-matter systems.

For two types of quintessence models having thawing and tracking properties, there exist analytic solutions for the dark energy equation of state $w$ expressed in terms of several free parameters. We put observational bounds on the parameters in such scenarios by using the recent type Ia supernovae, cosmic microwave background, and baryon acoustic oscillations data. The observational constraints are quite different depending on whether or not the recent baryon acoustic oscillations data from BOSS are taken into account. With the BOSS data the upper bounds of today’s values of $w$ ($=w_0$) in thawing models is very close to $-1$, whereas without this data the values of $w_0$ away from $-1$ can still be allowed. The tracker equation of state $w_{(0)}$ during the matter era is constrained to be $w_{(0)}<-0.949$ at 95% C.L. even without the BOSS data, so that the tracker models with $w$ away from $-1$ are severely disfavored. We also study observational constraints on scaling models in which $w$ starts to evolve from 0 in the deep matter era and show that the transition to the equation of state close to $w=-1$ needs to occur at an early cosmological epoch. In the three classes of quintessence models studied in this paper, the past evolution of the Hubble parameters in the best-fit models shows only less than a 2.5% difference compared to $\Lambda \mathrm{CDM}$.

We consider cosmological constraints arising from the background expansion history on the effective field theory of cosmic acceleration, a theoretical framework that allows for a unified way to classify both models of dark energy and modified gravity within the linear regime. In the Einstein frame, the most general action for the background can be written in terms of a canonical scalar field which is nonminimally coupled to matter. The leading corrections to the action are expressible through a quartic kinetic term, and scalar couplings to a Gauss-Bonnet curvature term and the Einstein tensor. We determine the implications of the terms in this general action for the predicted expansion history in the context of dynamical attractors. We find that each modifies the matter dominated and/or accelerative eras in ways that allow us to place cosmological constraints on them. We present current constraints on the effective action using the latest Type Ia supernovae, cosmic microwave background, and baryon acoustic oscillation data. This includes finding that the scalar field effective field theory with a coupled Gauss-Bonnet term and the data are significantly discrepant.

Halos are biased tracers of the dark matter distribution. It is often assumed that the initial patches from which halos formed are locally biased with respect to the initial fluctuation field, meaning that the halo-patch fluctuation field can be written as a Taylor series in the dark matter density fluctuation field. If quantities other than the local density influence halo formation, then this Lagrangian bias will generically be nonlocal; the Taylor series must be performed with respect to these other variables as well. We illustrate the effect with Monte Carlo simulations of a model in which halo formation depends on the local shear (the quadrupole of perturbation theory) and provide an analytic model that provides a good description of our results. Our model, which extends the excursion set approach to walks in more than one dimension, works both when steps in the walk are uncorrelated, as well as when there are correlations between steps. For walks with correlated steps, our model includes two distinct types of nonlocality: one is due to the fact that the initial density profile around a patch which is destined to form a halo must fall sufficiently steeply around it—this introduces $k$ dependence to even the linear bias factor, but otherwise only affects the monopole of the clustering signal. The other type of nonlocality is due to the surrounding shear field; this affects the quadratic and higher-order bias factors and introduces an angular dependence to the clustering signal. In both cases, our analysis shows that these nonlocal Lagrangian bias terms can be significant, particularly for massive halos; they must be accounted for in, e.g., analyses of higher-order clustering in Lagrangian or Eulerian space. Comparison of our predictions with measurements of the halo bispectrum in simulations is encouraging. Although we illustrate these effects using halos, our analysis and conclusions also apply to the other constituents of the cosmic web—filaments, sheets and voids.

In the Standard Model (SM) the hypercharges of quarks and leptons are not determined by the gauge group itself. In a recent paper [C. Hattori et al., Phys. Rev. D 83, 015009 (2011)] it is shown that if the direct product gauge group $G_{\mathrm{SM}}$ is slightly modified to the semidirect product group $G_{\mathrm{SM}}^{\prime }$, hypercharges are restricted to quantized values as $n/6$ $\mathrm{mod}\mathbb{Z}(n=0,1,3,4)$. In this brief paper, we examine all of the compact Lie groups locally isomorphic to $G_{\mathrm{SM}}$ and show that $G_{\mathrm{SM}}^{\prime }$ (or its isomorphisms) is the unique possibility that yields the correct hypercharge quantization.

We revisit an earlier calculation of the decay $H\to e\overline{e}\gamma$ using the recently reported mass value of the Higgs boson candidate observed in the ATLAS and CMS experiments together with cuts that are appropriate for experimental analyses.

We investigate the quark backreaction on the Polyakov loop and its impact on the thermodynamics of quantum chromodynamics. The dynamics of the gluons generating the Polyakov-loop potential is altered by the presence of dynamical quarks. However, this backreaction of the quarks has not yet been taken into account in Polyakov-loop extended model studies. In the present work, we show within a $2+1$ flavor Polyakov-quark-meson model that a quark-improved Polyakov-loop potential leads to a smoother transition between the low-temperature hadronic phase and the high-temperature quark-gluon plasma phase. In particular, we discuss the dependence of our results on the remaining uncertainties that are the critical temperature and the parametrization of the Polyakov-loop potential as well as the mass of the $\sigma$ meson.

In universal extra-dimensional models a conserved $Z_2$ parity ensures the stability of the lightest Kaluza-Klein particle, a potential dark-matter candidate. Boundary-localized kinetic terms, in general, do not preserve this symmetry. We examine, in the presence of such terms, the single production of Kaluza-Klein excitations of the neutral electroweak gauge bosons and their decay to zero-mode fermion-antifermion pairs. We explore how experiments at the Large Hadron Collider at CERN can constrain the boundary-localized kinetic terms for different choices of the compactification radius.