Matthew Buican

Exploring general gauge mediation

We explore various aspects of General Gauge Mediation (GGM). We present a reformulation of the correlation functions used in GGM, and further elucidate their IR and UV properties. Additionally we clarify the issue of UV sensitivity in the calculation of the soft masses in the MSSM, highlighting the role of the supertrace over the messenger spectrum. Finally, we present weakly coupled messenger models which fully cover the parameter space of GGM. These examples demonstrate that the full parameter space of GGM is physical and realizable. Thus it should be considered a valid basis for future phenomenological explorations of gauge mediation.

D-branes at singularities, compactification, and hypercharge

We report on progress towards the construction of SM-like gauge theories on the world-volume of D-branes at a Calabi-Yau singularity. In particular, we work out the topological conditions on the embedding of the singularity inside a compact CY threefold, that select hypercharge as the only light U(1) gauge factor. We apply this insight to the proposed open string realization of the SM of hep-th/0508089, based on a D3-brane at a dP8 singularity, and present a geometric construction of a compact Calabi-Yau threefold with all the required topological properties.

On the superconformal index of Argyres–Douglas theories

We conjecture a closed-form expression for the Schur limit of the superconformal index of two infinite series of Argyres-Douglas (AD) superconformal field theories (SCFTs): the (A1,A2n−3) and the (A1,D2n) theories. While these SCFTs can be realized at special points on the Coulomb branch of certain N = 2 gauge theories, their superconformal R symmetries are emergent, and hence their indices cannot be evaluated by localization. Instead, we construct the (A1,A2n−3) and (A1,D2n) indices by using a relation to two-dimensional qdeformed Yang-Mills theory and data from the class S construction. Our results generalize the indices derived from the torus partition functions of the two-dimensional chiral algebras associated with the (A1,A3) and (A1,D4) SCFTs. As checks of our conjectures, we study the consistency of our results with an S-duality recently discussed by us in collaboration with Giacomelli and Papageorgakis, we reproduce known Higgs branch relations, we check consistency with a series of renormalization group flows, and we verify that the small S 1 limits of our indices reproduce expected Cardy-like behavior. We will discuss the S 1

On the geometry of metastable supersymmetry breaking

We give a concise geometric recipe for constructing D-brane gauge theories that exhibit metastable SUSY breaking. We present two simple examples in terms of branes at deformed CY singularities.

Soft terms from broken symmetries

In theories of phyiscs beyond the Standard Model (SM), visible sector fields often carry quantum numbers under additional gauge symmetries. One could then imagine a scenario in which these extra gauge symmetries play a role in transmitting supersymmetry breaking from a hidden sector to the Supersymmetric Standard Model (SSM). In this paper we present a general formalism for studying the resulting hidden sectors and calculating the corresponding gauge mediated soft parameters. We find that a large class of generic models features a leading universal contribution to the soft scalar masses that only depends on the scale of Higgsing, even if the model is strongly coupled. As a by-product of our analysis, we elucidate some IR aspects of the correlation functions in General Gauge Mediation. We also discuss possible phenomenological applications.

SUSY breaking mediation by D-brane instantons

It is well known that D-brane instantons can generate contributions to the effective superpotential of gauge theories living on D-branes which are perturbatively forbidden by global U(1) symmetries. We extend this idea to theories with supersymmetry breaking, studying the effect of D-brane instantons stretched between the SUSY-breaking and visible sectors. Analogously to what happens in the SUSY case, this mechanism can give rise to perturbatively forbidden soft terms (among other effects). We introduce and discuss general properties of instanton mediation. We illustrate our ideas in simple Type IIB toroidal orientifolds. As a bi-product, we present a string theory realization of a Polonyi hidden sector.

Constraints on chiral operators in N = 2 SCFTs

A bstractWe study certain higher-spin chiral operators in N=2

On R-symmetric Fixed Points and Superconformality

\mathcal{N}=2