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In their study of spherical representations of an affine Lie algebra at the critical level and of unramified opers, Frenkel and Gaitsgory introduced what they called the Weyl module $\mathbb{V}^{\lambda}$ corresponding to a dominant weight $\lambda$. This object plays an important role in the theory. In arXiv:2012.01858, we introduced a possible analogue $\mathbb{V}^{{\lambda},{\mu}}$ of the Weyl module in the setting of opers with two singular points, and in the case of sl(2) we proved that it has the "correct" endomorphism ring. In this paper, we compute the semi-infinite cohomology of $\mathbb{V}^{{\lambda},{\mu}}$ and we show that it does not share some of the properties of the semi-infinite cohomology of the Weyl module of Frenkel and Gaitsgory. For this reason, we introduce a new module $\tilde{\mathbb{V}}^{{\lambda},{\mu}}$ which, in the case of sl(2), enjoys all the expected properties of a Weyl module., Comment: 23 pages

We study local opers with two singularities for the case of the Lie algebra sl(2), and discuss their connection with a two-variables extension of the affine Lie algebra. We prove an analogue of the Feigin-Frenkel theorem describing the centre at the critical level, and an analogue of a result by Frenkel and Gaitsgory that characterises the endomorphism rings of Weyl modules in terms of functions on the space of opers., Comment: 56 pages. Comments are very welcome!

For each integral dominant weight $\lambda$, we construct a twisted global section functor $\Gamma^{\lambda}$ from the category of critical twisted $D$-modules on affine Grassmannian to the category of $\lambda$-regular modules of affine Lie algebra at critical level. We proved that $\Gamma^{\lambda}$ is exact and faithful. This generalized the work of Frenkel and Gaitsgory in the case when $\lambda=0$., Comment: 19 pages, preliminary version

Let $\mathcal{A}_{crit}$ be the chiral algebra corresponding to the affine Kac-Moody algebra at the critical level $\hat{\mathfrak{g}}_{crit}$. Let $\mathfrak{Z}_{crit}$ be the center of $\mathcal{A}_{crit}$. The commutative chiral algebra $\mathfrak{Z}_{crit}$ admits a canonical deformation into a non-commutative chiral algebra $\mathcl{W}_{h}$. In this paper we will express the resulting first order deformation via the chiral algebra $\mathcal{D}_{crit}$ of chiral differential operators of $G((t))$ at the critical level.