Filtered deformations of Lie groupoids

Abstract: Let $G \rightrightarrows G<sup>{(0)}$ be a Lie groupoid, $\mathrm{A} G \rightarrow G<sup>{(0)}$ its Lie algebroid and $X_1, \dots, X_r$ a family of sections of $\mathrm{A} G$ satisfying a Lie bracket generating condition of Hörmander type. We aim to build a pseudodifferential calculus allowing to study a Helffer-Nourrigat's conjecture on the groupoid $G$; in particular, we want differential operators of the form $\sum_{i = 1}^r X_i<sup>2$ to have an invertible symbol. In this article we achieve the geometrical part of this construction by defining a "weighted" version of the deformation to the normal cone $$\mathrm{DNC}(G, G^{(0)}) \rightrightarrows G^{(0)} \times \mathbb{R}<em>+$$. Heuristically, we deform $G$ around $G<sup>{(0)}$ with a "zoom" parameter $t \in \mathbb{R}</em>+$ by stretching $G$ by $t$ in the directions of the sections $X_i$, $t<sup>2$ along $[X_i, X_j]$, $t<sup>3$ along $[X_i, [X_j, X_k]]$ etc. In the case where $G = M \times M$ we recover a construction of Mohsen, and when the structure is equiregular we recover a construction of van Erp-Yuncken.