Strings, Branes and the Search for Unification

Texas A&M Research Foundation, College Station TX

Investigators

Abstract

The three researchers on this proposal propose a program investigating fundamental aspects of string theory and M-theory and their implications for particle phenomenology and cosmology. One aspect of this project deals with the construction and implications for phenomenology of flux backgrounds for heterotic strings, which they denote by torsional heterotic geometries. The heterotic string is a natural setting to construct models of particle phenomenology. However, the role played by background H-flux has not been unraveled yet, even though it may profoundly influence the 4d low-energy effective action. In this project the PIs employ a strategy to obtain the first large class of torsional heterotic geometries by explicitly constructing their metric. The number of torsional heterotic geometries turns out to be of the same order of magnitude as the number of type II flux backgrounds. The explicit examples display an N=2,1,0, supersymmetry in 4d. Flux changes the 4d phenomenology and the PIs are investigating the implications of this new strategy. They propose strategies to obtain chiral matter and novel ways to break the E8 gauge symmetry to the standard model gauge group. These backgrounds stand a much better chance of admitting tractable world-sheet descriptions compared to the type II counterparts. The precise implications of torsional geometries for algebraic geometry such as the calculation of the exact moduli space of torsional geometries, the resolution of singularities, the construction of vector bundles and ultimately three-generation models with stabilized moduli is proposed. Evidence of string theory from cosmology will be explored in terms of a brane inflation model. String theory models make predictions for gravitational radiation and lead to strong non-Gaussianities in the cosmic microwave background. Several aspects of the duality between M-theory compactifications to 4d space-time and its boundary conformal field theories (CFT) will also be explored. The research also includes a systematic construction and possible string/M-theory embedding of new supergravities in diverse dimensions, exploration of infinite dimensional symmetries, and their implications for integrability in string theory in nontrivial backgrounds. Finally, the important question of the uniqueness of string theory as a candidate for a quantum theory of gravity will be addressed in the context of 3d quantum gravity and its dual CFT. The broader impacts of the project are related to the importance of testing string theory as theory that can describe experiments. The PIs are looking for ways to understand the experimental tests for Cosmology and particle physics. In the LHC era and with new satellites becoming available, it is vital to work out the connections between physics at the Planck scale and TeV scale physics, while advancing our knowledge in string cosmology. The final goal of this project is to unravel the imprints of high-energy physics onto our 4d world. At the same time the program is expected to have a profound impact on different areas of mathematics. Two of the PIs have just written an important book on string theory and M theory with John Schwartz, one of the founders of superstring theory. All three PIs are involved in disseminating information about string theory by giving talks at workshops and conferences as well as organizing workshops. They are also involved in collaborations with mathematicians to understand the topology and geometry of string theory.