Stable envelopes for slices of the affine Grassmannian

The affine Grassmannian associated to a reductive group $\mathbf{G}$ is an affine analogue of the usual flag varieties. It is a rich source of Poisson varieties and their symplectic resolutions. These spaces are examples of conical symplectic resolutions dual to the Nakajima quiver varieties. We study the cohomological stable envelopes of D. Maulik and A. Okounkov [arXiv:1211.1287] in this family. We construct an explicit recursive relation for the stable envelopes in the $\mathbf{G} = \mathbf{PSL}_2$ case and compute the first-order correction in the general case. This allows us to write an exact formula for multiplication by a divisor.