Representations of affine superalgebras and mock theta functions

Abstract: We show that the normalized supercharacters of principal admissible modules over the affine Lie superalgebra $\hat{s\ell}{2|1}$ (resp. $\hat{ps\ell}{2|2}$) can be modified, using Zwegers' real analytic corrections, to form a modular (resp. $S$-) invariant family of functions. Applying the quantum Hamiltonian reduction, this leads to a new family of positive energy modules over the N=2 (resp. N=4) superconformal algebras with central charge $3(1-\frac{2m+2}{M})$, where $m \in \mathbb{Z}{\geq 0}$, $M\in \mathbb{Z}{\geq 2}$, $\gcd(2m+2,M)=1$ if $m>0$ (resp. $6(\frac{m}{M}-1)$, where $m \in \mathbb{Z}{\geq 1}, M\in \mathbb{Z}{\geq 2}$, $\gcd(2m,M)=1$ if $m>1$), whose modified characters and supercharacters form a modular invariant family.