Lagrangian Solutions to the 2d Euler System with L1 Vorticity and Infinite Energy

We consider solutions to the two-dimensional incompressible Euler system with only integrable vorticity, thus with possibly locally infinite energy. With such regularity, we use the recently developed theory of Lagrangian flows associated to vector fields with gradient given by a singular integral in order to define Lagrangian solutions, for which the vorticity is transported by the flow. We prove strong stability of these solutions via strong convergence of the flow, under the only assumption of L weak convergence of the initial vorticity. The existence of Lagrangian solutions to the Euler system follows for arbitrary L vorticity. Relations with previously known notions of solutions are established.