¨ *Research in String Theory*

Moduli stabilization, SUSY breaking
and Cosmology in flux compactifications

Recently, substantial and real progress has been made towards finding promising non-trivial sectors of string theory, mainly in type IIB string theory. Background fluxes of the Maxwell fields which preserve Lorentz invariance in the four dimensional space-time can be turned on to get a whole new set of solutions: flux compactifications. A given flux background is characterized by a set of integers, thus at each point of a lattice whose dimension is determined by the type of string theory and the compactification, there exists a possible background for four dimensional physics. This is commonly referred to as the "discretuum". One of the most important realizations of the past few years is that these flux backgrounds generate a potential for many of the moduli, the complex structure moduli and the dilaton, thus giving rise for the first time to the exciting possibility of stabilizing all moduli and constructing a realistic particle physics phenomenology and cosmology. A suggestion for stabilizing the remaining moduli and getting a small and positive cosmological constant was subsequently made by Kachru, Kallosh, Linde and Trivedi and has been under active investigation.

The upshot of all this is a novel view
of the space of solutions of string theory, "the
stringy landscape" in which there is a very large number of candidate vacuua in the discretuum -
perhaps on the order of 10^{500}. Only a very small fraction of these
(less than 10^{-120}) would have
an acceptably small cosmological constant and satisfy the criterion of metastability, and when additional conditions such as
cosmological viability and particle physics constraints are added, this number
will no doubt be substantially reduced, however, it is still likely to be
extremely large. We aim to take advantage of this progress to construct viable
models of cosmology and particle physics in this framework.

Our main objective is to determine whether any of the vacuua in the landscape is an acceptable vacuum that can be used as a viable model of cosmology and particle physics. We will need to determine a meaningful set of priors that can define what constitutes an acceptable vacuum and a viable model and determine their phenomenological consequences.