Macroscopic estimate of the linear Boltzmann and Landau equations with Specular reflection boundary

In this short note, we prove an $L^6$-control of the macroscopic part of the linear Boltzmann and Landau equations. This result is an extension of the test function method of Esposito-Guo-Kim-Marra~\cite{EGKM}\cite{EGKM2} to the specular reflection boundary condition, in which we crucially used the Korn’s inequality \cite{DV2} and the system of symmetric Poisson equations \cite{Bernou}.