The second order Huang-Yang approximation to the Fermi thermodynamic pressure

TL;DR

This paper rigorously derives the second order Huang-Yang approximation for the thermodynamic pressure of a dilute Fermi gas at positive temperature, extending the validity of the formula up to a specific temperature range.

Contribution

It provides a rigorous proof of the second order Huang-Yang approximation for Fermi pressure at positive temperature, including a new conjecture on density approximation.

Findings

Valid up to temperature T<ρ^{2/3 + 1/6}

Includes a positive temperature correction term

Method covers zero temperature Huang-Yang formula

Abstract

We consider a dilute Fermi gas in the thermodynamic limit with interaction potential scattering length $\mathfrak{a}_0$ at temperature $T>0$. We prove the 2nd order Huang-Yang approximation for the Fermi pressure of the system, in which there is a 2nd order term carrying the positive temperature efffect.Our formula is valid up to the temperature $T<\rho^{\frac{2}{3}+\frac{1}{6}}$, which is, by scaling, also necessary for the Huang-Yang formula to hold. Here, $T_F\sim\rho^{\frac{2}{3}}$ is the Fermi temperature. We also establish during the course of the proof, a conjecture regarding the second order approximation of density $\rho$ by R. Seiringer \cite{FermithermoTpositive}. Our proof uses frequency localization techniques from the analysis of nonlinear PDEs and does not involve spatial localization or Bosonization. In particular, our method covers the classical Huang-Yang formula at zero temperature.