Victor Rotger, "Diagonal cycles and elliptic curves of rank two" I will describe recent work in collaboration with H. Darmon and A. Lauder on the construction of an Euler system of diagonal cycles in the Chow group of suitable fibrations of the product of three modular curves. According to the conjectures of Beilinson-Bloch, the behavior of these classes is governed by the L-function associated by Garrett to the convolution of three cuspidal eigenforms. I will explain how to deform p-adically these classes in order to shed new light on the conjecture of Birch&Swinnerton-Dyer in ranks 0, 1 and 2.