We review the basic notions of compactification in the presence of a background flux. In extra-dimensional models with more than five dimensions, Scherk and Schwarz boundary conditions have to satisfy ’t Hooft consistency conditions. Different vacuum configurations can be obtained, depending whether trivial or nontrivial ’t Hooft flux is considered. The presence of the magnetic background flux provides, in addition, a mechanism for producing four-dimensional chiral fermions. Particularizing to the six-dimensional case, we calculate the one-loop effective potential for a $U(N)$ gauge theory on ${\mathcal{M}}_4\times {\mathcal{T}}^2$. We first review the well-known results of the trivial ’t Hooft flux case, where one-loop contributions produce the usual Hosotani dynamical symmetry breaking. Finally we applied our result for describing, for the first time, the one-loop contributions in the nontrivial ’t Hooft flux case.

We derive the thermal correlators for twisted quantum fields on noncommutative spacetime. We show that the thermal expectation value of the number operator is same as in commutative spacetime, but that higher correlators are sensitive to the noncommutativity parameters ${\theta }^{\mu \nu }$.

We construct several new families of vacuum solutions that describe black holes in uniformly accelerated motion. They generalize the $C$ metric to the case where the energy density and tension of the strings that pull (or push) on the black holes are independent parameters. These strings create large curvatures near their axis and when they have infinite length they modify the asymptotic properties of the spacetime, but we discuss how these features can be dealt with physically, in particular, in terms of “wiggly cosmic strings.” We comment on possible extensions and extract lessons for the problem of finding higher-dimensional accelerating black hole solutions.

Extreme and very-near-extreme spin $J$ Kerr black holes have been conjectured to be holographically dual to two-dimensional (2D) conformal field theories (CFTs) with left and right central charges $c_L=c_R=12J$. In this paper it is observed that the 2D conformal symmetry of the scalar wave equation at low frequencies persists for generic nonextreme values of the mass $M\ne \sqrt{J}$. Interestingly, this conformal symmetry is not derived from a conformal symmetry of the spacetime geometry except in the extreme limit. The $2\pi$ periodic identification of the azimuthal angle $\varphi$ is shown to correspond to a spontaneous breaking of the conformal symmetry by left and right temperatures $T_L=M^2/2\pi J$ and $T_R=\sqrt{M^4-J^2}/2\pi J$. The well-known low-frequency scalar-Kerr scattering amplitudes coincide with correlators of a 2D CFT at these temperatures. Moreover, the CFT microstate degeneracy inferred from the Cardy formula agrees exactly with the Bekenstein-Hawking area law for all $M$ and $J$. These observations provide evidence for the conjecture that the Kerr black hole is dual to a $c_L=c_R=12J$ 2D CFT at temperatures ($T_L,T_R$) for every value of $M$ and $J$.

The $\gamma$-ray and neutrino emissions from dark matter (DM) annihilation in galaxy clusters are studied. After about one year of operation of Fermi-LAT, several nearby clusters are reported with stringent upper limits of GeV $\gamma$-ray emission. We use the Fermi-LAT upper limits of these clusters to constrain the DM model parameters. We find that the DM model distributed with substructures predicted in cold DM scenario is strongly constrained by Fermi-LAT $\gamma$-ray data. Especially for the leptonic annihilation scenario which may account for the $e^{\pm }$ excesses discovered by PAMELA/Fermi-LAT/HESS, the constraint on the minimum mass of substructures is of the level ${10}^2–{10}^3{\mathrm{M}}_{\odot }$, which is much larger than that expected in the cold DM picture, but is consistent with a warm DM scenario. We further investigate the sensitivity of neutrino detections of the clusters by IceCube. It is found that neutrino detection is much more difficult than $\gamma$-rays. Only for very heavy DM ($\sim 10\mathrm{TeV}$) together with a considerable branching ratio to line neutrinos the neutrino sensitivity is comparable with that of $\gamma$-rays.

Theories of gravity for which gravitons can be treated as massive particles have presently been studied as realistic modifications of general relativity, and can be tested with cosmological observations. In this work, we study the ability of a recently proposed theory with massive gravitons, the so-called Visser theory, to explain the measurements of luminosity distance from the Union2 compilation, the most recent Type-Ia Supernovae (SNe Ia) data set, adopting the current ratio of the total density of nonrelativistic matter to the critical density (${\Omega }_m$) as a free parameter. We also combine the SNe Ia data with constraints from baryon acoustic oscillations (BAO) and cosmic microwave background (CMB) measurements. We find that, for the allowed interval of values for ${\Omega }_m$, a model based on Visser’s theory can produce an accelerated expansion period without any dark energy component, but the combined analysis (SNe $\mathrm{Ia}+\mathrm{BAO}+\mathrm{CMB}$) shows that the model is disfavored when compared with the $\Lambda \mathrm{CDM}$ model.

The decade-old formulation of the isolated horizon classically and within loop quantum gravity, and the extraction of the microcanonical entropy of such a horizon from this formulation, is reviewed, in view of recent renewed interest. There are two main approaches to this problem: one employs an $SU(2)$ Chern-Simons theory describing the isolated horizon degrees of freedom, while the other uses a reduced $U(1)$ Chern-Simons theory obtained from the $SU(2)$ theory, with appropriate constraints imposed on the spectrum of boundary states “living” on the horizon. It is shown that both these ways lead to the same infinite series asymptotic in the horizon area for the microcanonical entropy of an isolated horizon. The leading area term is followed by an unambiguous correction term logarithmic in area with a coefficient $-\frac{3}{2}$, with subleading corrections dropping off as inverse powers of the area.

We discuss the properties of homogeneous and isotropic flat cosmologies in which the present accelerating stage is powered only by the gravitationally induced creation of cold dark matter (CCDM) particles (${\Omega }_m=1$). For some matter creation rates proposed in the literature, we show that the main cosmological functions such as the scale factor of the universe, the Hubble expansion rate, the growth factor, and the cluster formation rate are analytically defined. The best CCDM scenario has only one free parameter and our joint analysis involving baryonic acoustic oscillations + cosmic microwave background (CMB) + SNe Ia data yields ${\tilde{\Omega }}_m=0.28\pm 0.01$ ($1\sigma$), where ${\tilde{\Omega }}_m$ is the observed matter density parameter. In particular, this implies that the model has no dark energy but the part of the matter that is effectively clustering is in good agreement with the latest determinations from the large-scale structure. The growth of perturbation and the formation of galaxy clusters in such scenarios are also investigated. Despite the fact that both scenarios may share the same Hubble expansion, we find that matter creation cosmologies predict stronger small scale dynamics which implies a faster growth rate of perturbations with respect to the usual $\Lambda \mathrm{CDM}$ cosmology. Such results point to the possibility of a crucial observational test confronting CCDM with $\Lambda \mathrm{CDM}$ scenarios through a more detailed analysis involving CMB, weak lensing, as well as the large-scale structure.

Topological quantum interactions, namely, Chern-Simons terms and global Wess-Zumino terms, arise naturally in theories with extra dimensions of space compactified on orbifolds. If the extra dimensions become manifest at the TeV scale, experiments at the Large Hadron Collider (LHC) could observe signatures of topological interactions. Decays of Kaluza-Klein excitations of neutral electroweak gauge bosons into pairs of neutral standard model gauge bosons, $Z^0{Z}^0$ and $Z^0\gamma$, would provide a clean signature, since such decays do not occur at tree level. In this paper, we investigate the prospects for discovering such decays at the LHC, in the context of the Higgsless model of electroweak symmetry breaking. We identify the form of the relevant topological interactions, and estimate their strength. We find that in the minimal version of the model, the signal may be observed with about $100{\mathrm{fb}}^{-1}$ of data at the LHC using the Drell-Yan production process of the Kaluza-Klein gauge bosons. In addition, it is likely that the ultraviolet completion of the model would contain additional massive fermions, which can significantly enhance the signal. With two additional fermion multiplets, observation of the topological decay modes at the 3-sigma level would be possible with about $100{\mathrm{fb}}^{-1}$ of data using the highly model-independent vector-boson fusion production channel.

We consider a model of strong electroweak symmetry breaking in which the expectation value of an additional, possibly composite, scalar field is responsible for the generation of fermion masses. The dynamics of the strongly coupled sector is defined and studied via its holographic dual, and does not correspond to a simple, scaled-up version of QCD. We consider the bounds from perturbative unitarity, the $S$ parameter, and the mass of the Higgs-like scalar. We show that the combination of these constraints leaves a relatively limited region of parameter space viable, and suggests the qualitative features of the model that might be probed at the LHC.

The top-pair $t\overline{t}$ production cross section close to threshold in $e^{+}{e}^{-}$ collisions is strongly affected by the small lifetime of the top quark. Since the cross section is defined through final states containing the top decay products, a consistent definition of the cross section depends on prescriptions of how these final states are accounted for the cross section. Experimentally, these prescriptions are implemented, for example, through cuts on kinematic quantities such as the reconstructed top quark invariant masses. As long as these cuts do not reject final states that can arise from the decay of a top and an antitop quark with a small off-shellness compatible with the nonrelativistic power counting, they can be implemented through imaginary phase space matching conditions in nonrelativistic QCD. The prescription-dependent cross section can then be determined from the optical theorem using the $e^{+}{e}^{-}$ forward scattering amplitude. We compute the phase space matching conditions associated to cuts on the top and antitop invariant masses at next-to-next-to-leading logarithmic order and partially at next-to-next-to-next-to-leading logarithmic order in the nonrelativistic expansion accounting also for higher order QCD effects. Together with finite lifetime and electroweak effects known from previous work, we analyze their numerical impact on the $t\overline{t}$ cross section. We show that the phase space matching contributions are essential to make reliable nonrelativistic QCD predictions, particularly for energies below the peak region, where the cross section is small. We find that irreducible background contributions associated to final states that do not come from top decays are strongly suppressed and can be neglected for the theoretical predictions.

The Ernst method of removing nodal singularities from the charged C-metric representing a uniformly accelerated black hole with mass $m$, charge $q$ and acceleration $A$ by “adding” an electric field $E$ is generalized. Utilizing the new form of the C-metric found recently, Ernst’s simple “equilibrium condition” $mA=qE$ valid for small accelerations is generalized for arbitrary $A$. The nodal singularity is removed also in the case of accelerating and rotating charged black holes, and the corresponding equilibrium condition is determined.

Violations of Lorentz boost symmetry in the electron and photon sectors can be constrained by studying several different high-energy phenomenon. Although they may not lead to the strongest bounds numerically, measurements made in terrestrial laboratories produce the most reliable results. Laboratory bounds can be based on observations of synchrotron radiation, as well as the observed absences of vacuum Čerenkov radiation ($e^{\pm }\to e^{\pm }+\gamma$) and photon decay ($\gamma \to e^{+}+e^{-}$). Using measurements of synchrotron energy losses at LEP and the survival of TeV photons, we place new bounds on the three electron Lorentz-violation coefficients $c_{(TJ)}$, at the $3\times {10}^{-13}$ to $6\times {10}^{-15}$ levels.

The minimal supersymmetric standard model involves a rather restrictive Higgs potential with two Higgs fields. Recently, the full set of classes of symmetries allowed in the most general two-Higgs-doublet model was identified; these classes do not include the supersymmetric limit as a particular class. Thus, a physically meaningful definition of the supersymmetric limit must involve the interaction of the Higgs sector with other sectors of the theory. Here we show how one can construct basis invariant probes of supersymmetry involving both the Higgs sector and the gaugino-Higgsino-Higgs interactions.

We present results from the first lattice simulations of three-dimensional noncompact quantum electrodynamics (${\mathrm{QED}}_3$) with $N_f$ four-component fermion flavors coupled to a weak $Z_2$ chirally invariant four-fermi interaction. Results with $N_f\ge 4$ show that the scaling near the strong coupling chiral transition or sharp crossover is determined by the $3d$ Gross-Neveu ultraviolet-stable renormalization group fixed point. Small deviations of the $N_f=4$ critical exponents from the respective Gross-Neveu ones, hint at evidence for nonzero fermion mass generated by the gauge fields dynamics that might have been enhanced by the four-fermi coupling. It is also shown that the scaling region is suppressed at weak four-fermi couplings and large $N_f$ values. Measurements of (i) a monopole susceptibility which is the polarizability of the monopole configurations, and (ii) the density of isolated monopoles, imply that for $N_f\ge 1$ and weak gauge couplings the monopoles do not affect the theory’s confining properties, because they are shielded.

We investigate a linear sigma model with global chiral $U(2{)}_R\times U(2{)}_L$ symmetry. The mesonic degrees of freedom are the standard scalar and pseudoscalar mesons and the vector and axial-vector mesons. The baryonic degrees of freedom are the nucleon, $N$, and its chiral partner, $N^{*}$, which is usually identified with $N(1535)$. The chiral partner is incorporated in the so-called mirror assignment, where the nucleon mass is not solely generated by the chiral condensate but also by a chirally invariant mass term, $m_0$. The presence of (axial-) vector fields modifies the expressions for the axial-coupling constants of the nucleon, $g_A^N$, and its partner, $g_A^{N^{*}}$. Using experimental data for the decays $N^{*}\to N\pi$ and $a_1\to \pi \gamma$, as well as lattice results for $g_A^{N^{*}}$ we infer that in our model $m_0\sim 500\mathrm{MeV}$, i.e., an appreciable amount of the nucleon mass originates from sources other than the chiral condensate. We test our model by evaluating the decay $N^{*}\to N\eta$ and the $s$-wave nucleon-pion scattering lengths $a_0^{(\pm )}$.

We discuss the observed disagreement between the $Q^2$ distributions of neutrino-nucleus quasielastic events, measured by a number of recent experiments, and the predictions of Monte Carlo simulations based on the relativistic Fermi gas model. The results of our analysis suggest that these discrepancies are likely to be ascribable to both the breakdown of the impulse approximation and the limitations of the Fermi gas description. Several issues related to the extraction of the $Q^2$ distributions from the experimental data are also discussed, and new kinematical variables, which would allow for an improved analysis, are proposed.

We present a study of the decays $B^{0,+}\to J/\psi {\pi }^{+}{\pi }^{-}{\pi }^0{K}^{0,+}$, using $467\times {10}^6$ $B\overline{B}$ pairs recorded with the BABAR detector. We present evidence for the decay mode $X(3872)\to J/\psi \omega$, with product branching fractions $\mathcal{B}(B^{+}\to X(3872)K^{+})\times \mathcal{B}(X(3872)\to J/\psi \omega )=[0.6\pm 0.2(\mathrm{stat})\pm 0.1(\mathrm{syst})]\times {10}^{-5}$, and $\mathcal{B}(B^0\to X(3872)K^0)\times \mathcal{B}(X(3872)\to J/\psi \omega )=[0.6\pm 0.3(\mathrm{stat})\pm 0.1(\mathrm{syst})]\times {10}^{-5}$. A detailed study of the ${\pi }^{+}{\pi }^{-}{\pi }^0$ mass distribution from $X(3872)$ decay favors a negative-parity assignment.

We consider the continuum limit of a moose model corresponding to a generalization to $N$ sites of the degenerate BESS model. The five-dimensional formulation emerging in this limit is a realization of a RS1 type model with $SU(2{)}_L\otimes SU(2{)}_R$ in the bulk, broken by boundary conditions and a vacuum expectation value on the infrared brane. A low-energy effective Lagrangian is derived by means of the holographic technique and corresponding bounds on the model parameters are obtained.