The Z_2 Orbifold of the Universal Affine Vertex Algebra

Let $\gg$ be a simple, finite-dimensional complex Lie algebra, and let $V^k(\gg )$ denote the universal affine vertex algebra associated to $\gg$ at level $k$. The Cartan involution on $\gg$ lifts to an involution on $V^k(\gg )$, and we denote by $V^k(\gg {)}^{{\mathbb{Z}}_2}$ the orbifold, or fixed-point subalgebra, under this involution. Our main result is an explicit minimal strong finite generating set for $V^k(\gg {)}^{{\mathbb{Z}}_2}$ for generic values of $k$. In the case $\gg =\text{gs}{\text{gl}}_2$, we also determine the set of nongeneric values of $k$, where this set does not work.