Concentration of the invariant measures for the periodic Zakharov, KdV, NLS and Gross-Piatevskii equations in 1D and 2D

This paper concerns Gibbs measures ν for some nonlinear PDE over the D-torus TD. The Hamiltonian H=∫TD‖∇u‖2−∫TD|u|p has canonical equations with solutions in ΩN={u∈L2(TD):∫|u|2≤N}; this N is a parameter in quantum field theory analogous to the number of particles in a classical system. For D=1 and 2≤p<6, ΩN supports the Gibbs measure ν(du)=Z−1e−H(u)∏x∈Tdu(x) which is normalized and formally invariant under the flow generated by the PDE. The paper proves that (ΩN,‖⋅‖L2,ν) is a metric probability space of finite diameter that satisfies the logarithmic Sobolev inequalities for the periodic KdV, the focussing cubic nonlinear Schrödinger equation and the periodic Zakharov system. For suitable subset of ΩN, a logarithmic Sobolev inequality also holds in the critical case p=6. For D=2, the Gross-Piatevskii equation has H=∫T2‖∇u‖2−∫T2(V⁎|u|2)|u|2, for a suitable bounded interaction potential V and the Gibbs measure ν lies on a metric probability space (Ω,‖⋅‖H−s,ν) which satisfies LSI. In the above cases, (Ω,d,ν) is the limit in L2 transportation distance of finite-dimensional (Ωn,‖⋅‖,νn) given by Fourier sums.