Formal neighborhood in arc schemes

The Drinfeld-Grinberg-Kazhdan theorem highlights a remarkable feature 
of the formal neighborood of a non degenerate rational arc. Basically
it says that it is described, modulo a trivial factor, by a finite
number of parameters. We will give a detailed account of Drinfeld's arguments 
showing this result. At the end, I will discuss related results
obtained in a joint work with Julien Sebag.

The talk will be given in french, but I will write in english on the blackboard.