Fall 2010

We revisit the idea that stringy corrections to the Kahler potential in N=1 flux compactifications to four dimensions can qualitatively change the structure of the effective scalar potential even at large volume. Following recent work by Bobkov et al [arXiv:1003.1982], we find that there exist non-supersymmetric vacua, including metastable de Sitter spacetimes, when the alpha' corrections to the Kahler potential are combined with a single contribution to the non-perturbative superpotential by an ample divisor.

We present a new approach to the resummation of low transverse-momentum logarithms using Soft-collinear Effective Theory. This method avoids several pitfalls that plague the standard approach. After motivating the importance of this phase-space region for Tevatron and LHC analyses, we explain the approach. Numerical results for production of the W, Z and Higgs bosons at hadron colliders are presented.

I discuss how the results of dark matter experiments can be used to draw conclusions about the nature of WIMP dark matter that are to a large extent model-independent. Specifically, I show that combining the results of direct detection experiments with data from neutrino telescopes can help establish whether the dark matter particle is its own anti-particle. I go on to discuss how results from gamma ray telescopes can help identify the primary annihilation channel of dark matter.

Correlation functions of non-BPS operators in N=4 super-Yang-Mills theory are largely unknown. I will discuss a semiclassical approach for evaluating certain classes of such correlators at strong coupling. I will also describe integrability-based tools which can be used to evaluate certain components of three-point functions at weak coupling.

Models with an SU(3) × SU(3) color group have been proposed to explain the FNAL observations of a positive enhancement of the top quark forward-backward asymmetry relative to standard model predictions. We show that this class of models cannot explain the asymmetry while remaining consistent with other data, including flavor-changing neutral currents in the b-quark sector. Along the way, we examine specific models, phenomenological approaches, and the implications of new LHC bounds on colored gauge bosons. Finally, we consider the impact of extending the color group to SU(3) × SU(3) × SU(3), as one might if embedding the model in an extra-dimensional framework.

Our galaxy contains a great number of stellar mass compact objects which are generally thought to be black holes. Precise x-ray observations of a thermal spectrum of the accretion disk can be used to determine whether or not these objects are in fact the black holes predicted by general relativity. The Kerr metric is completely specified by two parameters: the mass, M, and the spin, J, of the compact object. All the terms in the multipole moment expansion of the gravitational field can be immediately deduced from these two quantities; thus the determination of the quadrupole moment can be used to test the Kerr nature of astrophysical black hole candidates. In this talk, I will discuss theoretical studies that allow current observational data of the X-ray spectrum of stellar-mass black hole candidates to already put interesting constraints on the interpretation of these objects.

Nonperturbative effects on D7-branes play a key role in flux compactifications of type IIB string theory, but are usually described only in the four-dimensional effective theory, precluding ten-dimensional analysis of the corresponding vacua. I will first argue that gaugino condensation on D7-branes sources three-form flux in ten dimensions. I will then present new supersymmetric solutions of ten-dimensional supergravity that encode gaugino condensation on (p,q) seven-branes. Applications of these results to four-dimensional cosmological model-building will be discussed.