Let N be an ideal in the ring O of gaussian integers. We consider the action of the motivic Galois group on the motivic fundamental group of the elliptic curve with CM by the ring O, punctured at the N-torsion points, and relate it to the geometry of the Bianchi threefold obtained by taking the quotient of the hyperbolic space by a congruence subgroup of GL(2,O) determined by the ideal N.
The absolute cohomological purity conjecture of Grothendieck proved by Gabber ensures that on regular schemes étale cohomology classes of fixed cohomological degree extend uniquely over closed subschemes of large codimension. I will discuss the corresponding phenomenon for flat cohomology. The talk is based on joint work with Peter Scholze.
Le programme de Langlands p-adique a pour origine les travaux de Serre et de Hida sur les familles p-adiques de formes modulaires et les représentations galoisiennes qui leur sont associées. Mazur, en collaboration avec Gouvéa et avec Coleman, a joué un grand rôle dans la maturation de ce programme, mais celui-ci n'a toujours pas de forme vraiment définitive. Je présenterai des travaux récents...
For L/K an extension of fields and V an algebraic variety over K say that V is Diophantine Stable for the extension L/K if V(L) = V(K). That is, if `V acquires no new rational points’ when one makes the field extension from K to L. I will describe some recent results joint with Karl Rubin regarding Diophantine Stability and give a survey of related recent statistics, heuristics, and conjectures.
