A Dynamical Approach to the Berezin--Li--Yau Inequality

Abstract: We develop a dynamical method for proving the sharp Berezin--Li--Yau inequality. The approach is based on the volume-preserving mean curvature flow and a new monotonicity principle for the Riesz mean $R_Λ(Ωt)$. For convex domains we show that $RΛ$ is monotone non-decreasing along the flow. The key input is a geometric correlation inequality between the boundary spectral density $Q_Λ$ and the mean curvature $H$, established in all dimensions: in $d=2$ via circular symmetrization, and in $d\ge 3$ via the boundary Weyl expansion together with the Laugesen--Morpurgo trace minimization principle. Since the flow converges smoothly to the ball, the monotonicity implies the sharp Berezin--Li--Yau bound for every smooth convex domain. As an application, we obtain a sharp dynamical Cesàro--Pólya inequality for eigenvalue averages.