Wreath Macdonald polynomials, quiver varieties, and quasimap counts

We study the $K$-theoretic enumerative geometry of cyclic Nakajima quiver varieties, with particular focus on ${\text{Hilb}}^m([{\mathbb{C}}^2\mathrm{/}{\mathbb{Z}}_l])$, the equivariant Hilbert scheme of points on ${\mathbb{C}}^2$. The direct sum over $m$ of the equivariant $K$-theories of these varieties is known to be isomorphic to the ring symmetric functions in $l$ colors, with structure sheaves of torus fixed points identified with wreath Macdonald polynomials. Using properties of wreath Macdonald polynomials and the recent identification of the Maulik-Okounkov quantum affine algebra for cyclic quivers with the quantum toroidal algebras of type $A$, we derive an explicit formula for the generating function of capped vertex functions of ${\text{Hilb}}^m([{\mathbb{C}}^2\mathrm{/}{\mathbb{Z}}_l])$ with descendants given by exterior powers of the $0$th tautological bundle. We also sharpen the large framing vanishing results of Okounkov, providing a class of descendants and cyclic quiver varieties for which the capped vertex functions are purely classical. Our results also suggest certain integrality and wall-crossing conjectures for capped vertex functions.