Foliation groupoids and their cyclic homology

In this paper we study the Lie groupoids which appear in foliation theory. A foliation groupoid is a Lie groupoid which integrates a foliation, or, equivalently, whose anchor map is injective. The first theorem shows that, for a Lie groupoid G, the following are equivalent: - G is a foliation groupoid, - G has discrete isotropy groups, - G is Morita equivalent to an etale groupoid. Moreover, we show that among the Lie groupoids integrating a given foliation, the holonomy and the monodromy groupoids are extreme examples. The second theorem shows that the cyclic homology of convolution algebras of foliation groupoids is invariant under Morita equivalence of groupoids, and we give explicit formulas. Combined with the previous results of Brylinski, Nistor and the authors, this theorem completes the computation of cyclic homology for various foliation groupoids, like the (full) holonomy/monodromy groupoid, Lie groupoids modeling orbifolds, and crossed products by actions of Lie groups with finite stabilizers. Some parts of the proof, such as the H-unitality of convolution algebras, apply to general Lie groupoids. Since one of our motivation is a better understanding of various approaches to longitudinal index theorems for foliations, we have added a few brief comments at the end of the second section.Comment: 18 page

Deformations of Lie brackets: cohomological aspects

We introduce a new cohomology for Lie algebroids, and prove that it provides a differential graded Lie algebra which ``controls'' deformations of the structure bracket of the algebroid. We also have a closer look at various special cases such as Lie algebras, Poisson manifolds, foliations, Lie algebra actions on manifolds.Comment: 17 pages, Revised version: small corrections, more references adde

On the developability of subalgebroids

In this paper, the Almeida-Molino obstruction to developability of transversely complete foliations is extended to Lie groupoids

On the integrability of subalgebroids

Let G be a Lie groupoid with Lie algebroid g. It is known that, unlike in the case of Lie groups, not every subalgebroid of g can be integrated by a subgroupoid of G. In this paper we study conditions on the invariant foliation defined by a given subalgebroid under which such an integration is possible. We also consider the problem of integrability by closed subgroupoids, and we give conditions under which the closure of a subgroupoid is again a subgroupoid

Representing topoi by topological groupoids

It is shown that every topos with enough points is equivalent to the classifying topos of a topological groupoid

General static spherically symmetric solutions in Horava gravity

We derive general static spherically symmetric solutions in the Horava theory of gravity with nonzero shift field. These represent "hedgehog" versions of black holes with radial "hair" arising from the shift field. For the case of the standard de Witt kinetic term (lambda =1) there is an infinity of solutions that exhibit a deformed version of reparametrization invariance away from the general relativistic limit. Special solutions also arise in the anisotropic conformal point lambda = 1/3.Comment: References adde

Relative compactness conditions for topos

In this paper a systematic study is made of various notions of proper map in the context of toposes Modulo some separation conditions a proper map Y X of spaces is generally understood to be a continuous function which preserves compactness of subspaces under inverse image and which therefore in particular has compact bers In this spirit a rst denition of proper map between toposes was put forward by Johnstone in There a map of toposes fF E was called proper if fF is a compact lattice object in the topos E This is probably the most direct way of expressing that F is compact when viewed as a topos over the base E In fact Johnstone used the term perfect rather than proper and developed the theory mostly in the context of localic maps between toposes se

Minimal fibrations of dendroidal sets

We prove the existence of minimal models for fibrations between dendroidal sets in the model structure for ∞–operads, as well as in the covariant model structure for algebras and in the stable one for connective spectra. We also explain how our arguments can be used to extend the results of Cisinski (2014) and give the existence of minimal fibrations in model categories of presheaves over generalized Reedy categories of a rather common type. Besides some applications to the theory of algebras over ∞–operads, we also prove a gluing result for parametrized connective spectra (or Γ–spaces)

On the universal enveloping algebra of a Lie-Rinehart algebra

We review the extent to which the universal enveloping algebra of a Lie-Rinehart algebra resembles a Hopf algebra, and refer to this structure as a Rinehart bialgebra. We then prove a Cartier-Milnor-Moore type theorem for such Rinehart bialgebras