Category O and asymptotic characters

This paper defines an asymptotic character map which is a morphism from the Grothendieck group of category O of an integral filtered quantization to rational functions on the Lie algebra of a torus. We show that the asymptotic character of a module computes the equivariant multiplicity of its characteristic cycle. We then apply this construction to truncated shifted Yangians coming from simple, simply-laced Lie algebras and draw connections with characters of modules over KLR algebras using an equivalence of categories of arXiv:1806.07519. Our main theorem shows how this new formalism gives formulas relating equivariant multiplicities of Mirković-Vilonen cycles and characters of modules over cyclotomic KLR algebras. We explain how this result provides evidence that the change-of-basis between Lusztig's dual canonical basis and the Mirković-Vilonen basis of C[N] is computed by a characteristic cycle map whose domain is category O for truncated shifted Yangians, implying that the coefficients are non-negative integers.