Search Talks

I will describe the emergence of geometric (Berry) phases in supersymmetric systems. In theories with degenerate states, non-Abelian geometric phases can arise. I show how supersymmetry helps to ensure the existence of this phenomenon by invoking the examples of systems with (2,2) and (4,4) supersymmetry. In the former, I show how instantons contribute crucially to the form of the non-Abelian phase. The latter system applies to D0-D4 brane dynamics in string theory, leading to a surprising re-interpretation of the Berry phase in terms of gravitational precession of a probe brane. Towards the end will comment on some work in progress on the geometric phase in (8,8) SUSY systems.

In this talk, I will talk about recent developments in studying strongly coupled gauge theory using the gauge/gravity duality in string theory. In particular, the inclusion of fundamental degrees of freedom and finite chemical potential is reviewed. As an example, I will discuss the results from analyzing the gravitational dual of a none-supersymmetric gauge theory at low temperature and finite baryon chemical potential.

Alternative gauge choices for worldsheet supersymmetry can elucidate dynamical phenomena obscured in the usual superconformal guage. In the particular example of the tachyonic E_8 heterotic string, we use a judicious gauge choice to show that the process of closed-string tachyon condensation can be understood in terms of a worldsheet super-Higgs effect. The worldsheet gravitino assimilates the goldstino and becomes a dynamical propagating field. Conformal, but not superconformal, invariance is maintained throughout.

While Calabi-Yau compactifications of string theory are mathematically elegant, they typically result in many massless scalars in the low-energy, four-dimensional theory. Thus, it is interesting to consider non-Kahler compactifications in the hopes of deriving more phenomenologically interesting models. These models have received little attention in the heterotic theory owing to their mathematical complexity, however in recent work we have found a potential way to derive interesting features of such compactifications using gauged linear sigma models.

We will consider stability in the string theory landscape. A survey over several classes of flux vacua with different characteristics indicates that the vast majority of flux vacua with small cosmological constant are unstable to rapid decay to a big crunch. Only vacua with large compactification radius or (approximately) supersymmetric configurations turn out to be long lived. We will speculate that regions of the landscape with approximate R-symmetry, while rare, might be cosmological attractors.

Warped backgrounds in string theory are useful tools for building phenomenological models of early universe cosmology and particle physics. In particular, warped backgrounds play an important role in constructing viable models of brane inflation and can help explain the presence of hierarchies in particle physics. One interesting feature of warped models is that subtle differences in the warped geometry can lead to significant differences in observational signatures in the CMB and at the LHC that can be used to distingiush different models. In this talk, I will discuss recent work in distinguishing different warped geometries through CMB and LHC observations.

We demonstrate a number of effective field theory constructions developed to capture the effects of new physics on the Higgs sector of the standard model. We demonstrate that as the self couplings of the Higgs could be significantly effected by new physics, novel phenomenology such as a two Higgs bound state (Higgsium) may be possible. We also demonstrate that the effects of new physics on the Higgs fermion couplings, and thus the Higgs width, could be significant. We show that it is possible this could happen while the new physics cannot be directly detected at LHC. This could lead to an early Higgs discovery or a missing Higgs in the first 100 fb^(-1) of data at LHC.

Cosmic strings are non-trivial configurations of scalar (and vector) fields that are stable on account of a topological conservation law. They can be formed in the early universe as it cools after the Big Bang. The scalar fields required to form cosmic strings arise naturally if Nature is supersymmetric at high energies. A common feature of supersymmetric theories are directions in the scalar potential that are extremely flat. Combining these two ingredients, the cosmic strings associated with supersymmetric flat directions are qualitatively different from ordinary cosmic strings. In particular, flat-direction strings have very stable higher-winding modes, and are very wide relative to the scale of their energy density. These novel features have important implications for the formation and evolution of a network of flat-direction cosmic strings in the early universe. They also affect the observational signatures of the strings, which include gravity waves, dark matter, and modifications to the nuclear abundances and the blackbody spectrum of the microwave background radiation