Particle theory

Abstract:

In a two-dimensional toy model, motivated from five-dimensional heterotic M theory, we study the collision of scalar field kinks with boundaries. By numerical simulation of the full two-dimensional theory, we find that the kink is always inelastically reflected with a model-independent fraction of its kinetic energy converted into radiation. We show that the reflection can be analytically understood as a fluctuation around the scalar field vacuum. This picture suggests the possibility of spontaneous emission of kinks from the boundary due to small perturbations in the bulk. We verify this picture numerically by showing that the radiation emitted from the collision of an initial single kink eventually leads to a bulk populated by many kinks. Consequently, processes changing the boundary charges are practically unavoidable in this system. We speculate that the system has a universal final state consisting of a stack of kinks, their number being determined by the initial energy. © 2004 The American Physical Society.

Abstract:

We compute the moduli Kähler potential for M theory on a compact manifold of [Formula Presented] holonomy in a large radius approximation. Our method relies on an explicit [Formula Presented] structure with small torsion, its periods and the calculation of the approximate volume of the manifold. As a verification of our result, some of the components of the Kähler metric are computed directly by integration over harmonic forms. We also discuss the modification of our result in the presence of codimension-four singularities and derive the gauge-kinetic functions for the massless gauge fields that arise in this case. © 2004 The American Physical Society.

Abstract:

We reiterate that there is no evidence that BL Lacs are sources of ultrahigh energy cosmic rays. © 2004 The American Physical Society.

Abstract:

We study the time evolution of freely rolling moduli in the context of M-theory on a G2 manifold. This free evolution approximates the correct dynamics of the system at sufficiently large values of the moduli when effects from non-perturbative potentials and flux are negligible. Moduli fall into two classes, namely bulk moduli and blow-up moduli. We obtain a number of non-trivial solutions for the time-evolution of these moduli. As a generic feature, we find the blow-up moduli always expand asymptotically at early and late time. © SISSA/ISAS 2004.

Abstract:

We study the deconfinement phase transition in SU(N) gauge theories for N=2,3,4,6,8. The transition is first order for N ≥ 3, with the strength increasing as N increases. We extrapolate Tc/σ to the continuum limit for each N, and observe a rapid approach to the large N limit. As N increases the phase transition becomes clear-cut on smaller spatial volumes, indicating the absence of (non-singular) finite volume corrections at N = ∞ - reminiscent of large N reduction. The observed rapid increase of the inter-phase surface tension with N may indicate that for N = ∞ the deconfinement transition cannot, in practise, occur. © 2004 Published by Elsevier B.V.