Around the Quantum Lenard-Balescu equation

In the mean-field regime, a gas of quantum particles with Boltzmann statistics can be described by the Hartree-Fock equation. This dynamics becomes trivial if the initial distribution of particle is invariant by translation. However, the first correction is given on time of order $O(N)$ by the quantum Lenard–Balescu equation. In the first part of the present article, we justify this equation until time of order $O((\log N{)}^{1-\delta })$ (for any $\delta \in (0,1)$). A similar phenomenon exists in the classical setting (with a similar validity time obtained by Duerinckx \cite{Duerinckx}). In a second time, we prove the convergence for dimension $d\ge 2$ of the solutions of the quantum Lenard–Balescu equation to the solutions of its classical counterpart in the semi-classical limit. This problem can be interpreted as a grazing collision limit: the quantum Lenard–Balescu equation looks like a cut-off Boltzmann equation, when the classical one looks like the Landau equation.