Reduced smooth stacks?

TL;DR

This paper develops a systematic framework for comparing the effects of Lie groupoids, establishing a notion of effect equivalence that aligns with Morita equivalence for orbifold groupoids, impacting the theory of smooth stacks.

Contribution

It introduces a rigorous method to compare effects of Lie groupoids and shows their equivalence aligns with Morita equivalence in orbifold cases.

Findings

Effects of Morita equivalent Lie groupoids are equivalent.

The new effect equivalence coincides with Morita equivalence for orbifold groupoids.

Provides a foundation for presentation theory of proper smooth stacks.

Abstract

An arbitrary Lie groupoid gives rise to a groupoid of germs of local diffeomorphisms over its base manifold, known as its effect. The effect of any bundle of Lie groups is trivial. All quotients of a given Lie groupoid determine the same effect. It is natural to regard the effects of any two Morita equivalent Lie groupoids as being equivalent. In this paper we shall describe a systematic way of comparing the effects of different Lie groupoids. In particular, we shall rigorously define what it means for two arbitrary Lie groupoids to give rise to equivalent effects. For effective orbifold groupoids, the new notion of equivalence turns out to coincide with the traditional notion of Morita equivalence. Our analysis is relevant to the presentation theory of proper smooth stacks.