Particle theory

Abstract:

Under certain conditions some solutions to five-dimensional heterotic M theory can be accurately described by the four-dimensional action of the theory. We consider the connection between solutions of four- and five-dimensional heterotic M theory when moving five-branes are present in the bulk. We begin by describing how to raise the known four-dimensional moving brane solutions to obtain approximate solutions to the five-dimensional theory, presenting for the first time the metric template necessary for this procedure. We then present the first solutions to the five-dimensional theory containing moving five-branes. We then discuss the correspondence between solutions of the five- and four-dimensional actions as presented. Specifically, we show that our exact, five-dimensional solution only corresponds to one of the previously known four-dimensional solutions when the embedded five-brane is static. In other words, higher Kaluza-Klein modes are essential in the description of the five-brane’s motion in our new solution. © 2002 The American Physical Society.

Abstract:

We calculate the light "glueball" mass spectrum in N f=2 lattice QCD using a fermion action that is nonperturbatively O(a) improved. We work at lattice spacings a∼0.1 fm and with quark masses that range down to about one-half the strange quark mass. We find the statistical errors to be moderate and under control on relatively small ensembles. We compare our mass spectrum to that of quenched QCD at the same value of a. While the tensor mass is the same (within errors), the scalar mass is significantly smaller in the dynamical lattice theory, by a factor of ∼0.84±0.03. We discuss what the observed mq dependence of this suppression tells us about the dynamics of glueballs in QCD. We also calculate the masses of flux tubes that wind around the spatial torus, and extract the string tension from these. As we decrease the quark mass we see a small but growing vacuum expectation value for the corresponding flux tube operators. This provides clear evidence for "string breaking" and for the (expected) breaking of the associated gauge center symmetry by sea quarks. © 2002 The American Physical Society.

Abstract:

We find quasinormal modes of near extremal black branes by solving a singular boundary value problem for the Heun equation. The corresponding eigenvalues determine the dispersion law for the collective excitations in the dual strongly coupled (Formula presented) supersymmetric Yang-Mills theory at finite temperature. © 2002 The American Physical Society.

Abstract:

We calculate the string tension and part of the mass spectrum of SU(4) and SU(6) gauge theories in 2+1 dimensions using lattice techniques. We combine these new results with older results for Nc=2, . . . ,5 so as to obtain more accurate extrapolations to Nc=∞. The qualitative conclusions of the earlier work are unchanged: SU(Nc∞) theories in 2+1 dimensions are linearly confining as N c→∞ the limit is achieved by keeping g2Nc fixed; SU(3), and even SU(2), are "close" to SU(∞). We obtain more convincing evidence than before that the leading large-Nc correction is O(1/N c2). We look for the multiplication of states that one expects in simple flux loop models of glueballs, but find no evidence for this. © 2002 The American Physical Society.

Abstract:

For many event-shape observables, the most difficult part of a resummation in the Born limit is the analytical treatment of the observable's dependence on multiple emissions, which is required at single logarithmic accuracy. We present a general numerical method, suitable for a large class of event shapes, which allows the resummation specifically of these single logarithms. It is applied to the case of the thrust major and the oblateness, which have so far defied analytical resummation and to the two-jet rate in the Durham algorithm, for which only a subset of the single logs had up to now been calculated. © SISSA/ISAS 2002.