Particle theory

Abstract:

After inflation occurs, a weakly coupled scalar field will in general not be in thermal equilibrium but have a distribution of values determined by the inflationary Hubble parameter. If such a field subsequently undergoes discrete symmetry breaking, then the different degenerate vacua may not be equally populated so the domain walls which form will be "biased" and the wall network will subsequently collapse. Thus the cosmological domain wall problem may be solved for sufficiently weakly coupled fields in a post inflationary universe. We quantify the criteria for determining whether this does happen, using a Higgs-like potential, with a spontaneously broken Z2 symmetry. © 2001 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.

Abstract:

The aim of this paper is to summarize the general status of our understanding of small-x physics. It is based on presentations and discussions at an informal meeting on this topic held in Lund, Sweden, in March 2001. This document also marks the founding of an informal collaboration between experimentalists and theoreticians with a special interest in small-x physics. This paper is dedicated to the memory of Bo Andersson, who died unexpectedly from a heart attack on March 4th, 2002.