String Defects, Supersymmetry and the Swampland

TL;DR

This paper explores the constraints on six-dimensional supergravity theories with minimal supersymmetry, testing recent conjectures through explicit models and examining the role of string defects and supersymmetry breaking.

Contribution

It provides a microscopic analysis of proposed swampland constraints, introduces null charge conjectures, and investigates the effects of supersymmetry breaking on these conditions.

Findings

Conjecture of null charges $Q \,\cdot\, Q=0$ for theories with tensor multiplets.

Exclusion of certain anomaly-free models lacking string or F-theory realization.

Constraints on string defect couplings in supersymmetry-breaking vacua.

Abstract

Recently, Kim, Shiu and Vafa proposed general consistency conditions for six dimensional supergravity theories with minimal supersymmetry coming from couplings to strings. We test them in explicit perturbative orientifold models in order to unravel the microscopic origin of these constraints. Based on the perturbative data, we conjecture the existence of null charges $Q \cdot Q=0 $ for any six-dimensional theory with at least one tensor multiplet, coupling to string defects of charge $Q$. We then include the new constraint to exclude some six-dimensional supersymmetric anomaly-free examples that have currently no string or F-theory realization. We also investigate the constraints from the couplings to string defects in case where supersymmetry is broken in tachyon free vacua, containing non-BPS configurations of brane supersymmetry breaking type, where the breaking is localized on antibranes. In this case, some conditions have naturally to be changed or relaxed whenever the string defects experience supersymmetry breaking, whereas the constraints are still valid if they are geometrically separated from the supersymmetry breaking source.