Holomorphic modular bootstrap revisited

Abstract: In this work we revisit the "holomorphic modular bootstrap", i.e. the classification of rational conformal field theories via an analysis of the modular differential equations satisfied by their characters. By making use of the representation theory of ${\rm PSL}(2,\mathbb{Z}_n)$, we describe a method to classify allowed central charges and weights $(c,h_i)$ for theories with any number of characters $d$. This allows us to avoid various bottlenecks encountered previously in the literature, and leads to a classification of consistent characters up to $d=5$ whose modular differential equations are uniquely fixed in terms of $(c,h_i)$. In the process, we identify the full set of constraints on the allowed values of the Wronskian index for fixed $d\leq 5$.