Particle theory

Abstract:

The hierarchical structure of fermion masses suggests an underlying family symmetry, spontaneously broken by the vacuum expectation value of moduli (familon) field, triggered by supersymmetry breaking. The familons also acquire non vanishing F-terms, typically of order (theta)m(3/2). These F-terms contribute to the soft trilinear couplings and lead to flavour changing and CP violating processes. Current experimental limits require the slepton mass be heavier then 300GeV and impose strong bounds on the right handed down quark quark mixing angles which are inconsistent with models relating them to neutrino mixing angles and favour a near symmetric form for the magnitude of the mass matrix elements. The decay mu -> e gamma should be very close to the present upper bound.

Abstract:

As a non-trivial check of the non-supersymmetric gauge/gravity duality, we use a near-extremal black brane background to compute the retarded Green's functions of the stress-energy tensor in N = 4 super-Yang-Mills (SYM) theory at finite temperature. For the long-distance, low-frequency modes of the diagonal components of the stress-energy tensor, hydrodynamics predicts the existence of a pole in the correlators corresponding to propagation of sound waves in the N = 4 SYM plasma. The retarded Green's functions obtained from gravity do indeed exhibit this pole, with the correct values for the sound speed and the rate of attenuation. © SISSA/ISAS 2003.

Abstract:

We investigate the properties of the deconfinement transition in SU(4) and SU(6) gauge theories. We find that it is a 'normal' first order transition in both cases, from which we conclude that the transition is first order in the N → ∞ limit. Comparing our preliminary estimates of the continuum values of Tc/√σ with existing values for SU(2) and SU(3) demonstrates a weak dependence on N for all values of N. © 2002 Published by Elsevier Science B.V.