We study the properties of anti–de Sitter black holes with a Gauss-Bonnet term for various horizon topologies $(k=0,\pm 1)$ and for various dimensions, with emphasis on the less well understood $k=-1$ solution. We find that the zero temperature (and zero energy density) extremal states are the local minima of the energy for AdS black holes with hyperbolic event horizons. The hyperbolic AdS black hole may be stable thermodynamically if the background is defined by an extremal solution and the extremal entropy is non-negative. We also investigate the gravitational stability of AdS spacetimes of dimensions $D>\mathrm{}4\mathrm{}$ against linear perturbations and find that the extremal states are still the local minima of the energy. For a spherically symmetric AdS black hole solution, the gravitational potential is positive and bounded, with or without the Gauss-Bonnet type corrections, while, when $k=-1,$ a small Gauss-Bonnet coupling, namely, $\alpha \ll l^2$ (where l is the curvature radius of AdS space), is found useful to keep the potential bounded from below, as required for stability of the extremal background.

We present observational constraints on a scalar-tensor gravity theory by ${\chi }^2$ test for the CMB anisotropy spectrum. We compare the WMAP temperature power spectrum with the harmonic attractor model, in which the scalar field has its harmonic effective potential with a curvature $\beta$ in the Einstein conformal frame and the theory relaxes toward Einstein gravity with time. We find that the present value of the scalar coupling, i.e., the present level of deviation from Einstein gravity $\left({\alpha }_0^2\right),$ is bounded to be smaller than $5\times {10}^{-4-7\beta }\left(2\mathrm{}\sigma \right),$ and ${10}^{-2-7\beta }\left(4\mathrm{}\sigma \right)$ for $0<\mathrm{}\beta <\mathrm{0.45.}\mathrm{}$ This constraint is much stronger than the bound from the solar system experiments for large $\beta$ models, i.e., $\beta >0.2\mathrm{}$ and 0.3 in $2\sigma$ and $4\sigma$ limits, respectively. Furthermore, within the framework of this model, the variation of the gravitational constant at the recombination epoch is constrained as $|{G(z=z}_{\mathrm{rec}})-G_0|{/G}_0<0.05(2\mathrm{}\sigma ),$ and $0.23\left(4\sigma \right).\mathrm{}$

We extend our previous analysis of the unitarized pion-nucleon scattering amplitude including up to fourth order terms in heavy baryon chiral perturbation theory. We pay special attention to the stability of the generated $\Delta \mathrm{}\left(1232\right)\mathrm{}$ resonance, the convergence problems, and the power counting of the chiral parameters.

The thermodynamics of the $O\left(N\right)\mathrm{}$ nonlinear sigma model in 1+1 dimensions is studied. We calculate the pressure to next-to-leading order in the $1/N$ expansion and show that at this order, only the minimum of the effective potential can be rendered finite by temperature-independent renormalization. To obtain a finite effective potential away from the minimum requires an arbitrary choice of prescription, which implies that the temperature dependence is ambiguous. We show that the problem is linked to thermal infrared renormalons.

A comparison of spectra obtained using the 1-loop MSSM and 2-loop $R_p$ MSSM renormalization group equations is presented. The influence of higher loop corrections and R-parity violating terms is discussed. Some numerical constraints on the R-parity violating parameters are also given.

We study the chiral properties of quenched domain wall fermions with several gauge actions. We demonstrate that the residual chiral symmetry breaking, which is present for a finite number of lattice sites in the fifth dimension ${(L}_s),$ can be substantially suppressed using improved gauge actions. In particular the Symanzik action, the Iwasaki action, and a renormalization group improved gauge action, called the doubly blocked Wilson (DBW2) action, are studied and compared to the Wilson action. All improved gauge actions studied show a reduction in the additive residual quark mass $m_{\mathrm{res}}.$ Remarkably, in the DBW2 case $m_{\mathrm{res}}$ is roughly two orders of magnitude smaller than the Wilson gauge action at $a^{-1}=2\mathrm{}\mathrm{GeV}$ and $L_s=16.\mathrm{}$ Significant reduction in $m_{\mathrm{res}}$ is also realized at stronger gauge coupling corresponding to $a^{-1}=1.3\mathrm{}\mathrm{GeV}.$ As our numerical investigation indicates, this reduction is achieved by reducing the number of topological lattice dislocations present in the gauge field configurations. We also present detailed results for the quenched light hadron spectrum and the pion decay constant using the DBW2 gauge action.

We study the effects of thermal fluctuations of gluons and the diquark pairing field on the superconducting-to-normal state phase transition in a three-flavor color superconductor, using the Ginzburg-Landau free energy. At high baryon densities, where the system is a type I superconductor, gluonic fluctuations, which dominate over diquark fluctuations, induce a cubic term in the Ginzburg-Landau free energy, as well as large corrections to quadratic and quartic terms of the order parameter. The cubic term leads to a relatively strong first order transition, in contrast with the very weak first order transitions in metallic type I superconductors. The strength of the first order transition decreases with increasing baryon density. In addition gluonic fluctuations lower the critical temperature of the first order transition. We derive explicit formulas for the critical temperature and the discontinuity of the order parameter at the critical point. The validity of the first order transition obtained in the one-loop approximation is also examined by estimating the size of the critical region.

We investigate the effects of a nonzero leptonic mixing angle ${\theta }_{13}$ on the solar neutrino day-night asymmetry. Using a constant matter density profile for the Earth and well-motivated approximations, we derive analytical expressions for the ${\nu }_e$ survival probabilities for solar neutrinos arriving directly at the detector and for solar neutrinos which have passed through the Earth. Furthermore, we numerically study the effects of a nonzero ${\theta }_{13}$ on the day-night asymmetry at detectors and find that they are small. Finally, we show that if the uncertainties in the parameters ${\theta }_{12}$ and $\Delta m^2$ as well as the uncertainty in the day-night asymmetry itself were much smaller than they are today, this effect could, in principle, be used to determine ${\theta }_{13}.$

We analyze the necessary and sufficient conditions for the preservation of supersymmetry for bosonic geometries of the form $R^{1,9-d}\times M_d,$ in the common Neveu-Schwarz–Neveu-Schwarz (NS-NS) sector of type II string theory and also type I or heterotic string theory. The results are phrased in terms of the intrinsic torsion of G structures and provide a comprehensive classification of static supersymmetric backgrounds in these theories. Generalized calibrations naturally appear since the geometries can always arise as solutions describing NS or type I or heterotic fivebranes wrapping calibrated cycles. Some new solutions are presented. In particular we find $d=6\mathrm{}$ examples with a fibered structure which preserve $\mathcal{N}=1,2,3\mathrm{}$ supersymmetry in type II and include compact type I or heterotic geometries.

Braneworld scenarios with compact extra dimensions need the volume of the extra space to be stabilized. Goldberger and Wise have introduced a simple mechanism, based on the presence of a bulk scalar field, able to stabilize the radius of the Randall-Sundrum model. Here, we transpose the same mechanism to generic single-brane and two-brane models, with one extra dimension and arbitrary scalar potentials in the bulk and on the branes. The single-brane construction turns out to be always unstable, independently of the bulk and brane potentials. In the case of two branes, we derive some generic criteria ensuring the stabilization or destabilization of the system.

The quasinormal modes of the Reissner-Nordström de Sitter black hole for massless Dirac fields are studied using the Pöshl-Teller potential approximation. We find that the magnitude of the imaginary part of the quasinormal frequencies decreases as the cosmological constant or the orbital angular momentum increases, but it increases as the charge or the overtone number increases. An interesting feature is that the imaginary part is almost linearly related to the real part as the cosmological constant changes for a fixed charge, and the linearity becomes better as the orbital angular momentum increases. We also prove exactly that the Dirac quasinormal frequencies are the same for opposite chirality.

A nonminimally coupled quintessence model is investigated and the conditions for a stationary solution to the coincidence problem are obtained. For a conformally coupled scalar field and dissipative matter, a general solution possessing late acceleration is found. It fits rather well the high redshift supernovae data and gives a good prediction of the age of the Universe. Likewise, the cold dark matter component dominates the cosmological perturbations at late times albeit they decrease with expansion.

Nucleation of branes by a four-form field has recently been considered in string motivated scenarios for the neutralization of the cosmological constant. An interesting question in this context is whether the nucleation of stacks of coincident branes is possible, and if so, at what rate does it proceed. Feng et al. have suggested that, at high ambient de Sitter temperature, the rate may be strongly enhanced, due to large degeneracy factors associated with the number of light species living on the worldsheet. This might facilitate the quick relaxation from a large effective cosmological constant down to the observed value. Here, we analyze this possibility in some detail. In four dimensions, and after the moduli are stabilized, branes interact via repulsive long range forces. Because of that, the Coleman–de Luccia (CdL) instanton for coincident brane nucleation may not exist, unless there is some short range interaction that keeps the branes together. If the CdL instanton exists, we find that the degeneracy factor depends only mildly on the ambient de Sitter temperature, and does not switch off even in the case of tunneling from flat space. This would result in catastrophic decay of the present vacuum. If, on the contrary, the CdL instanton does not exist, coincident brane nucleation may still proceed through a “static” instanton, representing pair creation of critical bubbles—a process somewhat analogous to thermal activation in flat space. In that case, the branes may stick together due to thermal symmetry restoration, and the pair creation rate depends exponentially on the ambient de Sitter temperature, switching off sharply as the temperature approaches zero. Such a static instanton may be well suited for the “saltatory” relaxation scenario proposed by Feng et al.

We demonstrate that a CERN LHC Higgs boson search in weak boson fusion production with subsequent decay to weak boson pairs is robust against extensions of the standard model or minimal supersymmetric standard model involving a large number of Higgs doublets. We also show that the transverse mass distribution provides unambiguous discrimination of a continuum Higgs signal from the standard model.

We present a scenario in which Yukawa-like R-parity violating (RPV) couplings are naturally suppressed. In our model, RPV is assumed to originate from the SUSY breaking mechanism and then transmitted into the SUSY Lagrangian only through soft SUSY breaking operators in the scalar potential. The RPV Yukawa-like operators of the superpotential, conventionally parametrized by the couplings $\lambda ,$ ${\lambda }^{\prime }$ and ${\lambda }^{″},$ are then generated through loops containing the SUSY scalars, the gauginos and the soft RPV interactions and are, therefore, manifest as effective operators with a typical strength of ${O(10\mathrm{}}^{-3}).\mathrm{}$

A generic feature of gauge-mediated supersymmetry breaking models is that the gravitino is the lightest supersymmetric particle (LSP). In order not to overclose the Universe, the gravitino LSP should be light enough $(\lesssim 1\mathrm{keV}),$ or appropriately heavy $\left(\gtrsim 1\mathrm{GeV}\right).\mathrm{}$ We study further constraints on the mass of the gravitino imposed by electroweak experiments: i.e., muon $g-2$ measurements, electroweak precision measurements, and direct searches for supersymmetric particles at CERN LEP2. We find that the heavy gravitino is strongly disfavored from the lower mass bound on the next-to-LSP. The sufficiently light gravitino, on the other hand, has rather sizable allowed regions in the model parameter space.

We use information about DIS and $J/\psi$ production on hydrogen to model the t dependence of the ${\gamma }^{*}N$ scattering amplitude. We investigate the profile function for elastic scattering of hadronic components of the virtual photon off both a nucleon and heavy nuclear target, and we estimate the value of the impact parameter where the blackbody limit is reached. We also estimate the fraction of the cross section that is due to hadronic configurations in the virtual photon wave function that approach the unitarity limit. We extract, from these considerations, approximate lower limits on the values of x where the leading twist approximation in DIS is violated. We observe that the blackbody limit may be approached within DESY HERA kinematics with $Q^2$ equal to a few ${\mathrm{GeV}}^2$ and $x\sim {10}^{-4}.$ Comparisons are made with earlier predictions by Munier et al., and the longitudinal structure function is compared with preliminary HERA data. The principle advantage of our method is that we do not rely solely on the t dependence of ρ-meson production data. This allows us to extend our analysis down to very small impact parameters and dipole sizes. Finally, we perform a similar calculation with a ${}^{208}\mathrm{Pb}$ target, and we demonstrate that the blackbody limit is already approached at $Q^2\sim 20{\mathrm{GeV}}^2$ and $x\sim {10}^{-4}.$

Clean predictions are presented for all the spin-averaged heavy-light meson spectroscopies. A new symmetry is identified wherein the energy eigenstates have a universal dependence on both the light and heavy quark masses. This universality is used in an efficient analysis of these mesons within the QCD string or flux tube picture. We give unique predictions for all the D, $D_s,$ B, and $B_s$ type mesons in terms of just four measured quantities.

It is shown that an effective theory with meron degrees of freedom produces confinement in SU(2) Yang-Mills theory. When the scale is set by the string tension, the action density and topological susceptibility are similar to those arising in lattice QCD. The potential for this effective theory to produce center symmetry in SU(2) is discussed.

A comparison of the linear sigma model $\left(\mathrm{L}\sigma \mathrm{M}\right)$ and chiral perturbation theory (ChPT) predictions for pion and kaon dynamics is presented. Lowest and next-to-leading order terms in the ChPT amplitudes are reproduced if one restricts to scalar resonance exchange. Some low energy constants of the order $p^4$ ChPT Lagrangian are fixed in terms of scalar meson masses. Present values of these low energy constants are compatible with the $\mathrm{L}\sigma \mathrm{M}$ dynamics. We conclude that more accurate values would be most useful either to falsify the $\mathrm{L}\sigma \mathrm{M}$ or to show its capability to shed some light on the controversial scalar physics.