Guglielmo Lockhart, University of Amsterdam
Title: 6d BPS strings from various angles
Abstract: A salient feature of 6d SCFTs is the existence on their tensor branch of self-dual strings that couple to the tensor multiplets. Upon compactification on a circle to 5d, bound states of wrapped strings are described by families of 2d N=(0,4) CFTs. Their elliptic genera encode the 5d BPS index of the compactified theory, as well as the superconformal index of the parent 6d SCFT. In this talk I discuss some complementary approaches that have been developed to study their properties. On the one hand, their elliptic genus can be obtained by computing the topological string partition function on an associated elliptic Calabi-Yau threefold. On the other hand, in a variety of cases one can find weakly coupled 2d UV theories that flow to the N=(0,4) CFTs in the IR. This makes it possible to compute elliptic genera and other RG-invariant properties of the (0,4) CFTs exactly, and can be checked against the topological string computations. Finally, in the case where the 6d SCFT has a simple, simply-laced gauge group, the self-dual strings play a dual role of instantons of the gauge group. In this case I will argue that the strings’ dynamics are captured by a twisted compactification of Minahan-Nemeschansky theories, and will use this perspective to identify the elliptic genus of one E6 instanton string.