F-theory and M-theory perspectives on N=2 supersymmetric gauge theories in four dimensions
Deformations of the original F-theory background are proposed. These lead to multiple new dualities and physical phenomena. We concentrate on one model where we let seven-branes wrap a multi-centered Taub-NUT space instead of R4. This configuration provides a successful F-theory embedding of a class of recently proposed four-dimensional N = 2 superconformal (SCFT) à la Gaiotto. Aspects of Argyres- Seiberg duality, of the new Gaiotto duality, as well as of the branes network of Benini- Benvenuti and Tachikawa are captured by our construction. The supergravity theory for the conformal case is also briefly discussed. Extending our construction to the non-conformal case, we find interesting cascading behavior in four-dimensional gauge theories with N = 2 supersymmetry. Since the analysis of this unexpected phenomenon is quite difficult in the language of type IIB/F-theory, we turn to the type IIA/M-theory description where the origin of the N = 2 cascade is clarified. Using the T-dual type IIA brane language, we first start by studying the N = 1 supersymmetric cascading gauge theory found in type IIB string theory on p regular and M fractional D3-branes at the tip of the conifold. We reproduce the supersymmetric vacuum structure of this theory. We also show that the IIA analog of the non-supersymmetric state found by Kachru, Pearson and Verlinde in the IIB description is metastable in string theory, but the barrier for tunneling to the supersymmetric vacuum goes to infinity in the field theory limit. We then use the techniques we have developed to analyze the N = 2 supersymmetric gauge theory corresponding to regular and fractional D3-branes on a near-singular K3, and clarify the origin of the cascade in this theory.