2-Equivariant 2-Vector bundles and 2K-theories

Abstract

We define 2-vector bundles over a Lie groupoid as pseudofunctors into the bicategory of finite-dimensional super algebras, bimodules, and intertwiners. The resulting 2K-theory, obtained as the Grothendieck completion of the homotopy category, is a category in which ordinary K-theory appears as the endomorphism ring of the trivial object and twisted K-theories as morphisms from the trivial object to twistings. We establish a biequivalence between this pseudofunctor model and the stacky model of Kristel-Ludewig-Waldorf. The theory is extended equivariantly for coherent Lie 2-groups, with explicit computations for abelian and discrete 2-groups that recover the representation rings predicted by Lurie's 2-equivariant elliptic cohomology. For the stringor bundle of Stolz-Teichner, we show that it is the filtered pseudocolimit of finite-dimensional approximants, embedding it into our 2K-theoretic framework. Finally, weak groupoid objects internal to a bicategory yield 2-orbifold 2-vector bundles and their 2K-theory, unifying the ordinary and equivariant settings.