On the semisimplicity of the category $KL_k$ for affine Lie superalgebras

Abstract: We study the semisimplicity of the category $KL_k$ for affine Lie superalgebras and provide a super analog of certain results from arXiv:1801.09880. Let $KL_k^{fin}$ be the subcategory of $KL_k$ consisting of ordinary modules on which the Cartan subalgebra acts semisimply. We prove that $KL_k^{fin}$ is semisimple when 1) $k$ is a collapsing level, 2) $W_k(\mathfrak{g}, \theta)$ is rational, 3) $W_k(\mathfrak{g}, \theta)$ is semisimple in a certain category. The analysis of the semisimplicity of $KL_k$ is subtler than in the Lie algebra case, since in super case $KL_k$ can contain indecomposable modules. We are able to prove that in many cases when $KL_k^{fin}$ is semisimple we indeed have $KL_k^{fin}=KL_k$, which therefore excludes indecomposable and logarithmic modules in $KL_k$. In these cases we are able to prove that there is a conformal embedding $W \hookrightarrow V_k(\mathfrak{g})$ with $W$ semisimple (see Section 10). In particular, we prove the semisimplicity of $KL_k$ for $\mathfrak{g}=sl(2\vert 1)$ and $k = -\frac{m+1}{m+2}$, $m \in {\mathbb Z}_{\ge 0}$. For $\mathfrak{g} =sl(m \vert 1)$, we prove that $KL_k$ is semisimple for $k=-1$, but for $k=1$ we show that it is not semisimple by constructing indecomposable highest weight modules in $KL_k^{fin}$.