S and T for SCFTs

We develop a general set of methods for computing the oblique electroweak parameters S and T for bottom-up and top-down motivated scenarios in which the Higgs weakly mixes with a superconformal extra sector. In addition to their utility in phenomenological studies, the observables S and T are also of purely theoretical interest as they are defined by correlation functions of broken symmetries. We show that in the limit where the extra sector enjoys an approximate custodial symmetry, the leading contributions to S and T can be recast as calculable data of the theory in the conformal phase. Using this result, we also obtain model-independent bounds on the sign and size of oblique electroweak corrections from unitary superconformal theories.