Particle theory

Abstract:

We present a new scenario for baryogenesis in the context of heterotic brane-world models. The baryon asymmetry of the universe is generated at a small-instanton phase transition which is initiated by a moving brane colliding with the observable boundary. We demonstrate, in the context of a simple model, that reasonable values for the baryon asymmetry can be obtained. As a byproduct we find a new class of moving-brane cosmological solutions in the presence of a perfect fluid. © 2002 The American Physical Society.

Abstract:

We present results for the static interquark potential, lightest glueballs, light hadron spectrum, and topological susceptibility using a nonperturbatively improved action on a 16³×32 lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units (∼1.7 fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavors of dynamical quarks. With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied (MPS/Mv ≥ 0.58, where PS denotes pseudoscalar and V denotes vector). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities. ©2002 The American Physical Society.

Abstract:

The effective action for five-dimensional heterotic M theory in the presence of five-branes is systematically derived from Hořava-Witten theory coupled to an M5-brane world-volume theory. This leads to a five-dimensional N=1 gauged supergravity theory on S¹/Z2 coupled to four-dimensional N=1 theories residing on the two orbifold fixed planes and an additional bulk three-brane. We analyze the properties of this action, particularly the four-dimensional effective theory associated with the domain-wall vacuum state. The moduli Kähler potential and the gauge-kinetic functions are determined along with the explicit relations between four-dimensional superfields and five-dimensional component fields. ©2002 The American Physical Society.

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.