Particle theory

Abstract:

We study rolling radii solutions in the context of the four- and five-dimensional effective actions of heterotic M theory. For the standard four-dimensional solutions with varying dilaton and T modulus, we find approximate five-dimensional counterparts. These are new, generically nonseparating solutions corresponding to a pair of five-dimensional domain walls evolving in time. Loop corrections in the four-dimensional theory are described by certain excitations of fields in the fifth dimension. We point out that the two exact separable solutions previously discovered are precisely the special cases for which the loop corrections are time independent. Generically, loop corrections vary with time. Moreover, for a subset of solutions they increase in time, evolving into complicated, nonseparating solutions. In this paper we compute these solutions to leading, nontrivial order. Using the equations for the induced brane metric, we present a general argument showing that the accelerating backgrounds of this type cannot evolve smoothly into decelerating backgrounds. ©2000 The American Physical Society.

Abstract:

We present a comprehensive study of five-dimensional brane-world models for neutrino physics based on flat compactifications. Particular emphasis is put on the inclusion of bulk mass terms. We derive a number of general results for such brane-world models with bulk mass terms. In particular, in the limit of small brane-bulk couplings, the electroweak eigenstates are predominantly given as a superposition of three light states with non-trivial small admixtures of bulk states. As a consequence, neutrinos can undergo standard oscillations as well as oscillation into bulk Kaluza-Klein states. We use this structure to construct a specific model based on ℤ2 orbifolding and bulk Majorana masses which is compatible with all observed oscillation phenomena. The solar neutrino deficit is explained by oscillations into sterile bulk states while the atmospheric neutrino deficit is due to νμ - ντ oscillations with naturally maximal mixing. In addition, the model can accommodate the LSND result and a significant neutrino dark matter component. We also analyze the constraints from supernova energy loss on neutrino brane-world theories and show that our specific model is consistent with these constraints.

Abstract:

The first part of this lecture quickly touches upon some important but infrequently discussed issues in large extra dimension and warped extra dimension scenarios, with particular reference to effects in the early universe. The second part discusses a modification and extension of an earlier proposal by Brown and Teitelboim to relax the effective cosmological term by nucleation of fundamental membranes.