Jacobson-Morozov Lemma for Algebraic Supergroups

Abstract

Given a quasi-reductive algebraic supergroup $G$, we use the theory of semisimplifications of symmetric monoidal categories to define a symmetric monoidal functor $\hat{I}{¦}_x:Rep(G)\to Rep(OSp(1|2))$ associated to any given element $x\in \mathrm{Lie}(G{)}_{\bar{1}}$. For nilpotent elements $x$, we show that the functor $\hat{I}{¦}_x$ can be defined using the Deligne filtration associated to $x$. We use this approach to prove an analogue of the Jacobson-Morozov Lemma for algebraic supergroups. Namely, we give a necessary and sufficient condition on odd nilpotent elements $x\in \mathrm{Lie}(G{)}_{\bar{1}}$ which define an embedding of supergroups $OSp(1|2)\to G$ so that $x$ lies in the image of the corresponding Lie algebra homomorphism.

v2: fixed reference in Section 6