The stranger things of symmetric product orbifold CFTs

Symmetric product orbifold theories are valuable due to their universal features at large N. Here we will demonstrate that they have features that are not as pervasive: we provide evidence of strange behaviour under deformations within their moduli space. To this end, we consider the symmetric product orbifold of tensor products of N = 2 super-Virasoro minimal models, and classify them according to two criteria. The first criterion is the existence of a single-trace twisted exactly marginal operator that triggers the deformation. The second criterion is a sparseness condition on the growth of light states in the elliptic genera. In this context we encounter a strange variety: theories that obey the first criterion but the second criterion falls into a Hagedorn-like growth. We explain why this may be counter-intuitive and discuss how it might be accounted for in conformal perturbation theory. We also find a new infinite class of theories that obey both criteria, which are necessary conditions for each moduli space to contain a supergravity point.

Automated summary

Symmetric product orbifold theories have universal features at large N, but they may exhibit strange behavior under deformations within their moduli space. By studying the symmetric product orbifold of tensor products of N = 2 super-Virasoro minimal models, we classify them based on the existence of a single-trace twisted exactly marginal operator and a sparseness condition on the growth of light states in the elliptic genera. We discover a strange variety of theories that satisfy the first criterion but exhibit Hagedorn-like growth according to the second criterion. We also find a new infinite class of theories that satisfy both criteria, which are necessary conditions for each moduli space to contain a supergravity point.