Bethe ansatz equations for orthosymplectic Lie superalgebras and self-dual superspaces
Kang Lu, Evgeny Mukhin
TL;DR
This work develops a concrete bridge between Bethe ansatz solutions for Gaudin models tied to orthosymplectic Lie superalgebras and algebraic-geometry frameworks. By introducing a reproduction procedure, it generates populations of Bethe roots whose associated symmetric rational pseudodifferential operator $\mathcal{R}$ remains invariant; the superkernel $W$ becomes a self-dual superspace, and the population is canonically identified with the variety of isotropic full superflags in $W$ and with symmetric complete factorizations of $\mathcal{R}$. The authors carefully treat the two main osp families, $\mathfrak{osp}_{2m+1|2n}$ and $\mathfrak{osp}_{2m|2n}$, including type-B/C/D root structures, extended parity sequences, and fake reproduction procedures, to obtain a unified geometrical picture akin to the Langlands-dual flag variety in the purely bosonic setting. The main theorem asserts a bijection among the Bethe population, isotropic superflags in $W$, and symmetric factorizations of $\mathcal{R}$ under a superfertility condition, thus connecting integrable models with isotropic flag geometry and offering pathways to understanding eigenstructures of Bethe subalgebras in a super setting. These results generalize and unify known type-B, type-C, and even-type D cases and pave the way for further extension to quasi-periodic boundary conditions and XXX-type BAE for orthosymplectic algebras.
Abstract
We study solutions of the Bethe ansatz equations associated to the orthosymplectic Lie superalgebras $\mathfrak{osp}_{2m+1|2n}$ and $\mathfrak{osp}_{2m|2n}$. Given a solution, we define a reproduction procedure and use it to construct a family of new solutions which we call a population. To each population we associate a symmetric rational pseudo-differential operator $\mathcal R$. Under some technical assumptions, we show that the superkernel $W$ of $\mathcal R$ is a self-dual superspace of rational functions, and the population is in a canonical bijection with the variety of isotropic full superflags in $W$ and with the set of symmetric complete factorizations of $\mathcal R$. In particular, our results apply to the case of even Lie algebras of type D${}_m$ corresponding to $\mathfrak{osp}_{2m|0}=\mathfrak{so}_{2m}$.
