We describe how a stable effective theory in which particles of the same fermion number attract may spontaneously break Lorentz invariance by giving a nonzero fermion number density to the vacuum (and therefore dynamically generating a chemical potential term). This mechanism yields a finite vacuum expectation value $〈\overline{\psi }{\gamma }^{\mu }\psi 〉,$ which we consider in the context of proposed models that require such a breaking of Lorentz invariance in order to yield composite degrees of freedom that act approximately like gauge bosons. We also make general remarks about how the background source provided by $〈\overline{\psi }{\gamma }^{\mu }\psi 〉$ could relate to work on signals of Lorentz violation in electrodynamics.

Motivated by recent studies on the uniqueness or nonuniqueness of higher dimensional black hole spacetime, we investigate the asymptotic structure of spatial infinity in n-dimensional spacetimes $(n>~4).$ It turns out that the geometry of spatial infinity does not have maximal symmetry due to the nontrivial Weyl tensor ${}^{\left(n-1\right)}{C}_{\mathrm{abcd}}$ in general. We also address static spacetime and its multipole moments $P_{a_1{a}_2\cdot \cdot \cdot a_s}.$ Contrasting with four dimensions, we stress that the local structure of spacetimes cannot be unique under fixed multipole moments in static vacuum spacetimes. For example, we consider the generalized Schwarzschild spacetimes which are deformed black hole spacetimes with the same multipole moments as spherical Schwarzschild black holes. To specify the local structure of the static vacuum solution we need some additional information, at least the Weyl tensor ${}^{\left(n-2\right)}{C}_{\mathrm{abcd}}$ at spatial infinity.

We consider the instability of the Friedmann world model to second order in perturbations. We present the perturbed set of equations up to second order in the Friedmann background world model with a general spatial curvature and cosmological constant. We consider systems with completely general imperfect fluids, minimally coupled scalar fields, an electromagnetic field, and generalized gravity theories. We also present the case of null geodesic equations, and one based on the relativistic Boltzmann equation. In due time, a decomposition is made for scalar-, vector-, and tensor-type perturbations which couple with each other to second order. A gauge issue is resolved to each order. The basic equations are presented without imposing any gauge condition, and thus in a gauge-ready form so that we can take full advantage of having gauge freedom in analyzing the problems. As an application we show that to second order in perturbation the relativistic pressureless ideal fluid of the scalar type reproduces exactly the known Newtonian result. As another application we rederive the large-scale conserved quantities (of the pure scalar and tensor perturbations) to second order, first shown by Salopek and Bond, now from the exact equations. Several other applications are shown as well.

We present a general slow-roll formalism within braneworld-motivated cosmologies with non-standard effective Friedmann equations. Full towers of parameters involving either the inflaton potential or the Hubble parameter are constructed and the dynamics of nontachyonic and tachyonic fields are considered in detail; exact cosmological solutions and the inflationary attractor condition are provided. We compare scalar-driven and tachyon-driven accelerating eras through slow-roll correspondence and the observational imprint on early-universe structures.

We study the influence of shower fluctuations, and the possible presence of different nuclear species in the primary cosmic ray spectrum, on the experimental determination of both shower energy and the proton air inelastic cross section from studies of the longitudinal development of atmospheric showers in fluorescence experiments. We investigate the potential of the track length integral and shower size at maximum as estimators of shower energy. We find that at very high energy $\left(\sim {10}^{19}-{10}^{20}\mathrm{eV}\right)$ the error of the total energy assignment is dominated by the dependence on the hadronic interaction model, and is of the order of 5%. At lower energy $\left(\sim {10}^{17}-{10}^{18}\mathrm{eV}\right),$ the uncertainty of the energy determination due to the limited knowledge of the primary cosmic ray composition is more important. The distribution of the shower maximum $X_{\max }$ is discussed as a measure of the proton-air cross section. Uncertainties in a possible experimental measurement of this cross section introduced by intrinsic shower fluctuations, the model of hadronic interactions, and the unknown mixture of primary nuclei in the cosmic radiation are numerically evaluated.

Relativistic spin-orbit and spin-spin couplings have been shown to modify the gravitational wave forms expected from inspiraling binaries with a black hole and a neutron star. As a result inspiral signals may be missed due to significant losses in signal-to-noise ratio, if precession effects are ignored in gravitational-wave searches. We examine the sensitivity of the anticipated loss of signal-to-noise ratio on two factors: the accuracy of the precessing wave forms adopted as the true signals and the expected distributions of spin-orbit tilt angles, given the current understanding of their physical origin. We find that the results obtained using signals generated by approximate techniques are in good agreement with the ones obtained by integrating the 2PN equations. This shows that a complete account of all high-order post-Newtonian effects is usually not necessary for the determination of detection efficiencies. Based on our current astrophysical expectations, large tilt angles are not favored and as a result the decrease in detection rate varies rather slowly with respect to the black hole spin magnitude and is within 20–30 % of the maximum possible values.

It has recently been pointed out that the 511 keV emission line detected by integral/SPI from the bulge of our galaxy could be explained by annihilations of light dark matter particles into $e^{+}{e}^{-}.$ If such a signature is confirmed, then one might expect a conflict with the interpretation of very high energy gamma rays if they also turn out to be due to dark matter annihilations. Here, we propose a way to accommodate the existence of both signals being produced by dark matter annihilations through the existence of two stable (neutral) dark matter particles, as is possible in theories inspired from $N=2\mathrm{}$ supersymmetry.

We present a likelihood analysis of the parameter space of the constrained minimal supersymmetric extension of the standard model (CMSSM), in which the input scalar masses $m_0$ and fermion masses $m_{1/2}$ are each assumed to be universal. We include the full experimental likelihood function from the CERN LEP Higgs boson search as well as the likelihood from a global precision electroweak fit. We also include the likelihoods for $\overrightarrow{b}s\gamma$ decay and (optionally) $g_{\mu }-2.$ For each of these inputs, both the experimental and theoretical errors are treated. We include the systematic errors stemming from the uncertainties in $m_t$ and $m_b,$ which are important for delineating the allowed CMSSM parameter space as well as calculating the relic density of supersymmetric particles. We assume that these dominate the cold dark matter density, with a density in the range favored by the Wilkinson Microwave Anisotropy Probe. We display the global likelihood function along cuts in the ${(m}_{1/2}{,m}_0)$ planes for $\tan \beta =10\mathrm{}$ and both signs of μ, $\tan \beta =35,$ $\mu <0,$ and $\tan \beta =50,$ $\mu >0,$ which illustrate the relevance of $g_{\mu }-2$ and the uncertainty in $m_t.$ We also display likelihood contours in the ${(m}_{1/2}{,m}_0)$ planes for these values of $\tan \beta .$ The likelihood function is generally larger for $\mu >0\mathrm{}$ than for $\mu <0\mathrm{}$ and smaller in the focus-point region than in the bulk and coannihilation regions, but none of these possibilities can yet be excluded.

We estimate the Cronin effect in pA collisions at the CERN LHC and at the BNL RHIC, using a Glauber-eikonal model of initial state multiparton interactions. For a correct determination of the initial parton flux, we upgrade the model cross section, taking carefully into account all kinematical constraints of each multiparton interaction process. As compared with previous results, derived with approximate kinematics, we obtain a softer spectrum of produced partons, while improving the agreement of the model with the recent measurements of ${\pi }^0$ production in $d+\mathrm{Au}$ collisions at $\sqrt{s}=200A\mathrm{GeV}.$

Bottom-quark-induced processes are responsible for a large fraction of the CERN Large Hadron Collider (LHC) discovery potential, in particular, for supersymmetric Higgs bosons. Recently, the discrepancy between exclusive and inclusive Higgs boson production rates has been linked to the choice of an appropriate bottom factorization scale. We investigate the process kinematics at hadron colliders and show that it leads to a considerable decrease in the bottom factorization scale. This effect is the missing piece needed to understand the corresponding higher order results. Our results hold generally for charged and for neutral Higgs boson production at the LHC as well as at the Fermilab Tevatron. The situation is different for single top quark production, where we find no sizable suppression of the factorization scale. Turning the argument around, we can specify how large are the collinear logarithms that can be resummed using the bottom parton picture.

We study T-odd gauge invariantly defined T-odd unintegrated gluon densities in QCD. The average $\perp$ momentum of the gluons in a $\perp$ polarized nucleon can be nonzero due to the Sivers mechanism. However, we find that the sum of the transverse momenta due to the Sivers mechanism from gluons and all quark flavors combined vanishes, i.e., $〈{\mathbf{k}}_{\mathbf{\perp },\mathbf{g}}〉+{\sum }_q〈{\mathbf{k}}_{\mathbf{\perp },\mathbf{q}}〉=0.\mathrm{}$

We write an explicit local action for a large extra dimension stabilization scenario due to Arkani-Hamed, Hall, Smith, and Weiner (AHSW). Our action allows the AHSW proposal to be generalized to non-Poincaré invariant configurations, supersymmetric extensions, quantum effective field theory, and cosmological scenarios. The central step in constructing the action is working in terms of the four form gauge field which is the “electric-magnetic” dual to the “magnetic” scalar of AHSW. The action is manifestly invariant under higher general coordinate invariance.

We investigate the possibility that the late acceleration observed in the rate of expansion of the Universe is due to vacuum quantum effects arising in curved spacetime. The theoretical basis of the vacuum cold dark matter (VCDM), or vacuum metamorphosis, cosmological model of Parker and Raval is reexamined and improved. We show, by means of a manifestly nonperturbative approach, how the infrared behavior of the propagator (related to the large-time asymptotic form of the heat kernel) of a free scalar field in curved spacetime leads to nonperturbative terms in the effective action similar to those appearing in the earlier version of the VCDM model. The asymptotic form that we adopt for the propagator or heat kernel at large proper time s is motivated by, and consistent with, particular cases where the heat kernel has been calculated exactly, namely in de Sitter spacetime, in the Einstein static universe, and in the linearly expanding spatially flat Friedmann-Robertson-Walker (FRW) universe. This large-s asymptotic form generalizes somewhat the one suggested by the Gaussian approximation and the R-summed form of the propagator that earlier served as a theoretical basis for the VCDM model. The vacuum expectation value for the energy-momentum tensor of the free scalar field, obtained through variation of the effective action, exhibits a resonance effect when the scalar curvature R of the spacetime reaches a particular value related to the mass of the field. Modeling our Universe by an FRW spacetime filled with classical matter and radiation, we show that the back reaction caused by this resonance drives the Universe through a transition to an accelerating expansion phase, very much in the same way as originally proposed by Parker and Raval. Our analysis includes higher derivatives that were neglected in the earlier analysis, and takes into account the possible runaway solutions that can follow from these higher-derivative terms. We find that the runaway solutions do not occur if the universe was described by the usual classical FRW solution prior to the growth of vacuum energy density and negative pressure (i.e., vacuum metamorphosis) that causes the transition to an accelerating expansion of the universe in this theory.

In this paper we investigate asymptotic isotropization. We derive the asymptotic dynamics of spatially inhomogeneous cosmological models with a perfect fluid matter source and a positive cosmological constant near the de Sitter equilibrium state at late times, and near the flat FL equilibrium state at early times. Our results show that there exists an open set of solutions approaching the de Sitter state at late times, consistent with the cosmic no-hair conjecture. On the other hand, solutions that approach the flat FL state at early times are special and admit a so-called isotropic initial singularity. For both classes of models the asymptotic expansion of the line element contains an arbitrary spatial metric at leading order, indicating asymptotic spatial inhomogeneity. We show, however, that in the asymptotic regimes this spatial inhomogeneity is significant only at superhorizon scales.

In this paper, we investigate the dynamics and the evolution of the scale factor of a probe $\mathrm{D}p-\mathrm{brane}$ which moves in the background of source $\mathrm{D}p-\mathrm{branes}.$ The action of the probe brane is described by the Born-Infeld action and the interaction with the background Ramond-Ramond field. When the probe brane moves away from the source branes, it expands as a power law whose index depends on the dimension of the brane. If the energy density of the gauge field on the brane is subdominant, the expansion decelerates irrespective of the dimension of the brane. On the other hand, when the probe brane is a Nambu-Goto brane, the energy density of the gauge field can be dominant, in which case accelerating expansion occurs for $p<~4.$ The accelerating expansion stops when the brane has expanded sufficiently that the energy density of the gauge field becomes subdominant.

We consider bound states of two mesons (antimesons) in lattice quantum chromodynamics in an Euclidean formulation. For simplicity, we analyze an SU(3) theory with a single flavor in $2+1$ dimensions and two-dimensional Dirac matrices. For a small hopping parameter κ and small plaquette coupling $g_0^{-2},$ such that $0<\mathrm{}{g}_0^{-2}\ll \kappa \ll 1,$ recently we showed the existence of a (anti)mesonlike particle, with an asymptotic mass of the order of $-2\ln \kappa$ and with an isolated dispersion curve—i.e., an upper gap property persisting up to near the meson-meson threshold which is of the order of $-4\ln \kappa .$ Here, in a ladder approximation, we show that there is no meson-meson (or antimeson-antimeson) bound state solution to the Bethe-Salpeter equation up to the two-meson threshold. Remarkably the absence of such a bound state is an effect of a potential which is nonlocal in space at order ${\kappa }^2,$ i.e., the leading order in the hopping parameter κ. A local potential appears only at order ${\kappa }^4$ and is repulsive. The relevant spectral properties for our model are unveiled by considering the correspondence between the lattice Bethe-Salpeter equation and a lattice Schrödinger resolvent equation with a nonlocal potential.

We discuss the influence of closed Dirac strings on the photon propagator in the Landau gauge emerging from a study of the compact $U\left(1\right)\mathrm{}$ gauge model in $2+1$ dimensions. This gauge also minimizes the total length of the Dirac strings. Closed Dirac strings are stable against local gauge-fixing algorithms only due to the torus boundary conditions of the lattice. We demonstrate that these leftover Dirac strings are responsible for the previously observed unphysical behavior of the propagator of spacelike photons ${(D}_T)$ in the deconfinement (high temperature) phase. We show how one can monitor the number $N_3$ of thermal Dirac strings which allows us to separate the propagator measurements into $N_3$ sectors. The propagator in $N_3\ne 0$ sectors is characterized by a nonzero mass and an anomalous dimension similarly to the confinement phase. Both the mass squared and anomalous dimension are found to be proportional to $N_3.$ Consequently, in the $N_3=0\mathrm{}$ sector the unphysical behavior of the $D_T$ photon propagator is cured and the deviation from the free massless propagator disappears.

An approach is proposed to calculate generalized parton distributions (GPDs) in a constituent quark model (CQM) scenario, considering the constituent quarks as complex systems. The GPDs are obtained from the wave functions of the nonrelativistic CQM of Isgur and Karl, convoluted with the GPDs of the constituent quarks themselves. The latter are modeled by using the structure functions of the constituent quark, the double distribution representation of GPDs, and a recently proposed phenomenological constituent quark form factor. The present approach permits us to access a kinematical range corresponding to both the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi and the Efremov-Radyushkin-Brodsky-Lepage regions, for small values of the momentum transfer and of the skewedness parameter. In this kinematical region, the cross sections relevant to deeply virtual Compton scattering could be estimated by using the obtained GPDs. As an example, the leading twist, unpolarized GPD H has been calculated. Its general relations with the nonrelativistic definition of the electric form factor and with the leading twist unpolarized quark density are consistently recovered from our expressions. Further natural applications of the proposed approach are addressed.

The exclusive semileptonic heavy baryon decay ${\Lambda }_b\to p\mathcal{l}\overline{\nu }$ is investigated using the light-cone sum rule method in both full QCD and heavy quark effective theory (HQET). The form factors describing the decay are calculated and used to predict the decay width and differential distribution. The total decay width obtained from full QCD is in agreement with the previous theoretical predictions, while the HQET result is typically one order smaller. Both results are consistent with the experimental upper limit and can be compared to refined experimental data in the future.

We consider nonleptonic Cabibbo-allowed ${\Lambda }_b$ decays in the factorization approximation. We calculate nonleptonic decays of the type ${\Lambda }_b\to {\Lambda }_{c}P$ and ${\Lambda }_b\to {\Lambda }_{c}V$ relative to $\overline{B_d^0}\to D^{+}P$ and $\overline{B_d^0}\to D^{+}V$ where we include among the pseudoscalar states and the vector states the newly discovered $D_s$ resonances, $D_s\mathrm{}\left(2317\right)\mathrm{}$ and $D_s\mathrm{}\left(2460\right).$ In the ratio of ${\Lambda }_b$ decays to $D_s\mathrm{}\left(2317\right)\mathrm{}$ and $D_s\mathrm{}\left(2460\right)\mathrm{}$ relative to the $\overline{B_d^0}$ decays to these states, the poorly known decay constants of $D_s\mathrm{}\left(2317\right)\mathrm{}$ and $D_s\mathrm{}\left(2460\right)\mathrm{}$ cancel, leading to predictions that can shed light on the nature of these new states. In general, we predict the ${\Lambda }_b$ decays to be larger than the corresponding $\overline{B_d^0}$ decays and in particular we find the branching ratio for ${\Lambda }_b\to {\Lambda }_c{D}_s\mathrm{}\left(2460\right)\mathrm{}$ can be between four to five times the branching ratio for $\overline{B_d^0}\to D^{+}{D}_s\mathrm{}\left(2460\right).$ This enhancement of ${\Lambda }_b$ branching ratios follows primarily from the fact that more partial waves contribute in ${\Lambda }_b$ decays than in $\overline{B_d^0}$ decays. Our predictions are largely independent of model calculations of hadronic inputs like form factors and decay constants.