A second order upper bound on the ground state energy of a Bose gas beyond the Gross-Pitaevskii regime

Abstract

We consider a system of $N$ bosons in a unitary box in the grand-canonical setting interacting through a potential with scattering length scaling as $N^{-1+\kappa },$ $\kappa \in (0,2/3).$ This regimes interpolate between the Gross-Pitaevskii regime ($\kappa =0$) and the thermodynamic limit ($\kappa =2/3$). In Forum Math. Sigma 9 (2021), e74, as an intermediate step to prove an upper bound in agreement with the Lee-Huang-Yang formula in the thermodynamic limit, it is obtained a second order upper bound on the ground state energy for $\kappa <5/9.$ In this paper, thanks to a more careful analysis of the error terms, we extend the above mentioned result to $\kappa <7/12$.

Contribution to the Proceedings of ICMP 2021

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