Recently, Hashimoto and Thomas [J. High Energy Phys., 01 (2006) 083] found that noncommutative super Yang-Mills (NCSYM) theory with space-dependent noncommutativity can be formulated as a decoupling limit of open strings ending on D3-branes wrapping a Melvin universe supported by a flux of the NSNS $B$-field. Under $S$-duality, we show that this theory turns into a noncommutative open string (NCOS) theory with space-dependent space-time noncommutativity and effective space-dependent string scale. It is an NCOS theory with both space-dependent space-space and space-time noncommutativities under more general $SL(2,\mathbb{Z})$ transformation. These space-dependent noncommutative theories (NCSYM and NCOS) have completely the same thermodynamics as that of ordinary super YM theory, NCSYM and NCOS theories with constant noncommutativity in the dual supergravity description. Starting from black D3-brane solution in the Melvin universe and making a Lorentz boost along one of spatial directions on the worldvolume of D3-branes, we show that the decoupled theory is a lightlike NCSYM theory with space-dependent noncommutativity in a static frame or in an infinite-momentum frame depending on whether there is a gravitational pp-wave on the worldvolume of the D3-branes.

This paper is devoted to the study of the dynamics of the Dp-branes, F-strings and M-branes in the background of the system of two stacks of five-branes in type IIA, IIB, and M theory that intersect on the line.

We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics in the presence of weak magnetic fields using Schwinger-Dyson equations. Contrary to the case where the magnetic field is strong, in the weak field limit the coupling should exceed certain critical value in order for the generation of masses to take place, just as in the case where no magnetic field is present. The weak field limit is defined as $eB\ll m(0{)}^2$, where $m(0)$ is the value of the dynamically generated mass in the absence of the field. We carry out a numerical analysis to study the magnetic field dependence of the mass function above critical coupling and show that in this regime the dynamically generated mass and the chiral condensate for the lowest Landau level increase proportionally to $(eB{)}^2$.

We consider the possibility of energy being exchanged between the scalar and matter fields in scalar-tensor theories of gravity. Such an exchange provides a new mechanism which can drive variations in the gravitational “constant” $G$. We find exact solutions for the evolution of spatially flat Friedmann-Robertson-Walker cosmologies in this scenario and discuss their behavior at both early and late times. We also consider the physical consequences and observational constraints on these models.

Density perturbations generated from inflation almost always have a spectral index $n_s$ which runs (varies with the wavelength). We explore a running spectral index scenario in which the scalar spectral index runs from blue ($n_s>1$) on large length scales to red ($n_s<1$) on short length scales. Specifically, we look for a correlation between the length scale at which $n_s-1=0$ and the length scale at which tensor to scalar ratio $\mathcal{T}/\mathcal{S}$ reaches a minimum for single field slow-roll inflationary models. By computing the distribution of length scale ratios, we conclude that there indeed is a new approximate consistency condition that is characteristic of running spectral index scenarios that run from blue to red. Specifically, with strong running, we expect 96% of the slow-roll models to have the two length scales to be within a factor of 2, with the length scale at which the tensor to scalar ratio reaching a minimum longer than the wavelength at which $n_s-1=0$.

In this paper we apply second-order gauge-invariant perturbation theory to investigate the possibility that the coupling between gravitational waves (GWs) and a large-scale inhomogeneous magnetic field acts as an amplification mechanism in an “almost” Friedmann-Lemaître-Robertson-Walker Universe. The spatial inhomogeneities in the magnetic field are consistently implemented using the magnetohydrodynamic (MHD) approximation, which yields an additional source term due to the interaction of the magnetic field with velocity perturbations in the plasma. Comparing the solutions with the corresponding results in our previous work indicates that, on superhorizon scales, the interaction with the spatially inhomogeneous field in the dust regime induces the same boost as the case of a homogeneous field, at least in the ideal MHD approximation. This is attributed to the observation that the MHD induced part of the generated field effectively only contributes on scales where the coherence length of the initial field is less than the Hubble scale. At subhorizon scales, the GW induced magnetic field is completely negligible in relation to the MHD induced field. Moreover, there is no amplification found in the long-wavelength limit.

We study collision of two domain walls in five-dimensional asymptotically anti–de Sitter spacetime. This may provide the reheating mechanism of an ekpyrotic (or cyclic) brane universe, in which two Bogomol’nyi-Prasad-Sommerfield branes collide and evolve into a hot big bang universe. We evaluate a change of scalar field making the domain wall and can investigate the effect of a negative cosmological term in the bulk to the collision process and the evolution of our universe.

Large-scale magnetic fields can affect scalar cosmological perturbations whose evolution is described in the conformally Newtonian gauge and within the tight coupling approximation. The magnetized curvature perturbations present after matter-radiation equality (and prior to decoupling) are computed in terms of an appropriate transfer matrix allowing a general estimate of the Sachs-Wolfe plateau. From the observation that CMB initial conditions should be (predominantly) adiabatic, the contribution of the magnetic field intensity can be constrained.

Infrared features of the ghost propagator of color-diagonal and color antisymmetric ghost propagator of quenched SU(2) and quenched SU(3) are compared with those of unquenched Kogut-Susskind fermion SU(3) lattice Landau gauge. We compare (i) the fluctuation of the ghost propagator, (ii) the ghost condensate parameter $v$ of the local composite operator (LCO) approach, and (iii) the Binder cumulant of color antisymmetric ghost propagator between quenched and unquenched configurations. The color-diagonal SU(3) ghost dressing function of unquenched configurations has weaker singularity than the quenched configurations. In both cases fluctuations become large in $q<0.5\mathrm{GeV}$. The ghost condensate parameter $v$ in the ghost propagator of the unquenched ${\mathrm{MILC}}_c$ configuration samples is $\sim 0.002–0.04{\mathrm{GeV}}^2$ while that of the SU(2) parallel tempering samples is consistent with 0. The Binder cumulant defined as $U(q)=1-\frac{1}{3}\frac{⟨{\overrightarrow{\varphi }}^4⟩}{(⟨{\overrightarrow{\varphi }}^2⟩{)}^2}$, where $\overrightarrow{\varphi }(q)$ is the color antisymmetric ghost propagator measured by the sample average of gauge fixed configurations via parallel tempering method, becomes $\sim 4/9$ in all the momentum region. The Binder cumulant of the color antisymmetric ghost propagator of quenched SU(2) can be explained by the 3D Gaussian distribution, but that of the unquenched ${\mathrm{MILC}}_c$ deviates slightly from that of the eight-dimensional Gaussian distribution. The stronger singularity and large fluctuation in the quenched configuration could be the cause of the deviation of the Kugo-Ojima confinement parameter $c$ from 1, and the presence of ordering in the ghost propagator of unquenched configurations makes it closer to 1.

We investigate the semileptonic OZI-forbidden annihilation decays $B_c^{-}\to {\eta }^{\prime }(\eta ,{\pi }^0)l^{-}\overline{\nu }$ for $l=\mu ,e$ in the perturbative QCD, and carry out a precise calculation without any approximation for the one-loop contributions, which involves integrals of 4- and 5-point loop functions. Our results show that the branching ratios of decays $B_c^{-}\to {\eta }^{\prime }{l}^{-}\overline{\nu }$, $B_c^{-}\to \eta l^{-}\overline{\nu }$, and $B_c^{-}\to {\pi }^0{l}^{-}\overline{\nu }$ turn out to be of orders ${10}^{-4}$, ${10}^{-5}$, and ${10}^{-6}$, respectively, which could be observable in the future experiments at the LHC.

We search for the charmed pentaquark candidate reported by the H1 collaboration, the ${\Theta }_c(3100{)}^0$, in $e^{+}{e}^{-}$ interactions at a center-of-mass (c.m.) energy of 10.58 GeV, using $124{\mathrm{fb}}^{-1}$ of data recorded with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ facility at SLAC. We find no evidence for such a state in the same $p{D}^{*-}$ decay mode reported by H1, and we set limits on its production cross section times branching fraction into $p{D}^{*-}$ as a function of c.m. momentum. The corresponding limit on its total rate per $e^{+}{e}^{-}\to q\overline{q}$ event, times branching fraction, is about 3 orders of magnitude lower than rates measured for the charmed ${\mathit{\Lambda }}_c$ and ${\mathit{\Sigma }}_c$ baryons in such events.

In this paper we use the deformation procedure introduced in former work on deformed defects to investigate several new models for real scalar field. We introduce an interesting deformation function, from which we obtain two distinct families of models, labeled by the parameters that identify the deformation function. We investigate these models, which identify a broad class of polynomial interactions. We find exact solutions describing global defects, and we study the corresponding stability very carefully.

A classical precursor to a full quantum dynamics for causal sets has been formulated in terms of a stochastic sequential growth process in which the elements of the causal set arise in a sort of accretion process. The transition probabilities of the Markov growth process satisfy certain physical requirements of causality and general covariance, and the generic solution with all transition probabilities nonzero has been found. Here we remove the assumption of nonzero probabilities, define a reasonable extension of the physical requirements to cover the case of vanishing probabilities, and find the completely general solution to these physical conditions. The resulting family of growth processes has an interesting structure reminiscent of an “infinite tower of turtles” cosmology.

In this work a detailed spectral analysis of the time series of the ${}^8\mathrm{B}$ solar neutrino flux published by the Super-Kamiokande Collaboration is presented, performed through a likelihood scan approach. Preliminarily a careful review of the analysis methodology is given, showing that the traditional periodicity search via the Lomb-Scargle periodogram is a special case of a more general likelihood based method. Since the data are published together with the relevant asymmetric errors, it is then shown how the likelihood analysis can be performed either with or without a prior error averaging. A key point of this work is the detailed illustration of the mathematical model describing the statistical properties of the estimated spectra obtained in the various cases, which is also validated through extensive Monte Carlo computations; the model includes a calculation for the prediction of the possible alias effects. In the successive investigation of the data, such a model is used to derive objective, mathematical predictions which are quantitatively compared with the features observed in the experimental spectra. This article clearly demonstrates that the handling of the errors is the origin of the discrepancy between published null observations and claimed significant periodicity in the same SK-I data sample. Moreover, the comprehensive likelihood analysis with asymmetric errors developed in this work provides results which cannot exclude the null hypothesis of constant rate, even though some indications stemming from the model at odd with such conclusion point towards the desirability of additional investigations with alternative methods to shed further light on the characteristics of the data.

We search for coincident gravitational wave signals from inspiralling neutron star binaries using LIGO and TAMA300 data taken during early 2003. Using a simple trigger exchange method, we perform an intercollaboration coincidence search during times when TAMA300 and only one of the LIGO sites were operational. We find no evidence of any gravitational wave signals. We place an observational upper limit on the rate of binary neutron star coalescence with component masses between 1 and $3M_{\odot }$ of 49 per year per Milky Way equivalent galaxy at a 90% confidence level. The methods developed during this search will find application in future network inspiral analyses.

We present results for masses of excited mesons from quenched calculations using chirally improved quarks at pion masses down to 350 MeV. The key features of our analysis are the use of a matrix of correlators from various source and sink operators and a basis which includes quark sources with different spatial widths, thereby improving overlap with states exhibiting radial excitations.

We study the properties of the color-Coulomb string tension obtained from the instantaneous part of gluon propagators in Coulomb gauge using quenched $SU(3)$ lattice simulation. In the confinement phase, the dependence of the color-Coulomb string tension on the QCD coupling constant is smaller than that of the Wilson loop string tension. On the other hand, in the deconfinement phase, the color-Coulomb string tension does not vanish even for $T/T_c=1\sim 5$, the temperature dependence of which is comparable with the magnetic scaling, dominating the high temperature QCD. Thus, the color-Coulomb string tension is not an order parameter of quark-gluon plasma phase transition.

We study the effects of gauge-field fluctuations on the free energy density of a homogeneous color superconductor in the color-flavor-locked (CFL) phase. Gluonic fluctuations induce a strong first-order phase transition, in contrast to electronic superconductors where this transition is weakly first order. The critical temperature for this transition is larger than the one corresponding to the diquark pairing instability. The physical reason is that the gluonic Meissner masses suppress long-wavelength fluctuations as compared to the normal conducting phase where gluons are massless, which stabilizes the superconducting phase. In weak coupling, we analytically compute the temperatures associated with the limits of metastability of the normal and superconducting phases, as well as the latent heat associated with the first-order phase transition. We then extrapolate our results to intermediate densities and numerically evaluate the temperature of the fluctuation-induced first-order phase transition, as well as the discontinuity of the diquark condensate at the critical point. We find that the London limit of magnetic interactions is absent in color superconductivity.

The present work has two goals. The first is to complete the classification of geometries in terms of torsion classes of M-branes wrapping cycles of a Calabi-Yau manifold. The second goal is to give insight into the physical meaning of the torsion class constraints. We accomplish both tasks by defining new energy minimizing calibrations in M-brane backgrounds. When fluxes are turned on, it is these calibrations that are relevant, rather than those which had previously been defined in the context of purely geometric backgrounds.

We calculate the energy of a static string in an anti-de Sitter (AdS) slice between two D3-branes with orbifold condition. The energy for configurations with end points on a brane grows linearly for large separation between these points. The derivative of the energy has a discontinuity at some critical separation. Choosing a particular position for one of the branes we find configurations with smooth energy. In the limit where the other brane goes to infinity the energy has a Coulombian behavior for short separations and can be identified with the Cornell potential for a quark antiquark pair. This identification leads to effective values for the AdS radius, the string tension and the position of the infrared brane. These results suggest an approximate duality between static strings in an AdS slice and a heavy quark antiquark configuration in a confining gauge theory.