Universal features of BPS strings in six-dimensional SCFTs

Del Zotto, Michele; Lockhart, Guglielmo

Abstract

In theories with extended supersymmetry the protected observables of UV superconformal fixed points are found in a number of contexts to be encoded in the BPS solitons along an IR Coulomb-like phase. For six-dimensional SCFTs such a role is played by the BPS strings on the tensorial Coulomb branch. In this paper we develop a uniform description of the worldsheet theories of a BPS string for rank-one 6d SCFTs. These strings are the basic constituents of the BPS string spectrum of arbitrary rank six-dimensional models, which they generate by forming bound states. Motivated by geometric engineering in F-theory, we describe the worldsheet theories of the BPS strings in terms of topologically twisted 4d N=2 theories in the presence of 1/2-BPS 2d (0, 4) defects. As the superconformal point of a 6d theory with gauge group G is approached, the resulting worldsheet theory flows to an N=(0, 4) NLSM with target the moduli space of one G instanton, together with a nontrivial left moving bundle characterized by the matter content of the six-dimensional model. We compute the anomaly polynomial and central charges of the NLSM, and argue that the 6d flavor symmetry F is realized as a current algebra on the string, whose level we compute. We find evidence that for generic theories the G dependence is captured at the level of the elliptic genus by characters of an affine Kac-Moody algebra at negative level, which we interpret as a subsector of the chiral algebra of the BPS string worldsheet theory. We also find evidence for a spectral flow relating the R-R and NS-R elliptic genera. These properties of the string CFTs lead to constraints on their spectra, which in combination with modularity allow us to determine the elliptic genera of a vast number of string CFTs, leading also to novel results for 6d and 5d instanton partition functions.

Citation

Del Zotto, M., & Lockhart, G. (2018). Universal features of BPS strings in six-dimensional SCFTs. Journal of High Energy Physics, 2018(8), Article 173. https://doi.org/10.1007/jhep08%282018%29173

• Journal Article Type: Article
• Acceptance Date: Aug 19, 2018
• Online Publication Date: Aug 28, 2018
• Publication Date: Aug 28, 2018
• Deposit Date: Oct 22, 2018
• Publicly Available Date: Oct 22, 2018
• Journal: Journal of High Energy Physics
• Print ISSN: 1126-6708
• Electronic ISSN: 1029-8479
• Publisher: Scuola Internazionale Superiore di Studi Avanzati (SISSA)
• Peer Reviewed: Peer Reviewed
• Volume: 2018
• Issue: 8
• Article Number: 173
• DOI: https://doi.org/10.1007/jhep08%282018%29173
• Public URL: https://durham-repository.worktribe.com/output/1344787