High Energy Physics

We study 5d and 6d SCFTs with eight supercharges by using 5-brane web diagrams in Type IIB string theory. There are two important properties of the web diagram. One is that it enables us to compute the exact partition function of the 5d theory on the 5-brane web. Even though the web diagram is not dual to a toric geometry, we develop a technique to compute the partition function by using the topological vertex. The other is that a new class of the 5-brane web diagram is conjectured to imply that the corresponding 5d theory has a 6d superconformal fixed point at high energies. Such a web diagram is called Tao web diagram. By using the Tao web diagram, we conjecture new 5d theories whose UV completion is a 6d SCFT. Moreover, we can show that a brane configuration realizing the 6d SCFT may reduce to the Tao web diagram, giving a direct way of identifying the 6d description of the 5d theory. This construction also indicates various dualities of the 5d theories.

Extensions of the Standard Model (SM) Higgs sector often predict the existence of new vacua and can feature novel patterns of symmetry breaking in the early universe. In this talk, I will discuss the implications of such scenarios for electroweak scale cosmology, baryogenesis, and Higgs phenomenology. I will focus on two classes of models, one involving a gauge singlet scalar field and the other an inert SU(2) doublet scalar. The former can give rise to a strong first-order electroweak phase transition, but also to rapidly expanding bubbles which can pose a problem for viable electroweak baryogenesis. In the latter, electroweak symmetry can be spontaneously broken by a first-order phase transition to an exotic vacuum, allowing for successful electroweak baryogenesis decoupled from the Standard Model-like Higgs field. Nevertheless, this class of scenarios generically predicts modifications of the SM-like Higgs couplings within reach of present-day collider experiments.