A simple proof of convergence to the Hartree dynamics in Sobolev trace norms

TL;DR

This paper provides a simple proof demonstrating convergence of the N-body Bosonic system to the Hartree dynamics in Sobolev trace norms, including energy trace norm, under minimal initial regularity assumptions.

Contribution

It offers a straightforward proof of convergence in Sobolev trace norms for the Hartree limit, extending previous results to stronger norms without requiring complex techniques.

Findings

Proves convergence in energy trace norm without rates

Establishes convergence in weaker Sobolev trace norms with rates

Requires only H^1-regularity of initial data

Abstract

The derivation of the Hartree equation from many-body systems of Bosons in the mean field limit has been very intensively studied in the last couple of years. However, very few results exist showing convergence of the k-th marginal of the N-body density matrix to the projection to the k-fold tensor product of the solution of the Hartree equation in stronger trace norms like the energy trace norm, see \cite{MS}, \cite{Lu}. This issue is from a physical view point very important. The reason is that one can then approximate expectation values of certain observables of the N-body system by means of the Hartree equation, with relaxation of the very restrictive assumption that the observables are bounded operators. Here we consider the non-relativistic case. We prove, assuming only H^1-regularity of the initial data, convergence in the energy trace norm without rates, and convergence in any other weaker Sobolev trace norm with rates. Our proof is simple and uses the functional $a_N$ introduced by Pickl in \cite{Pi}.