Logarithmic Sobolev and exponential inequalities for submanifolds in Cartan--Hadamard manifolds

Abstract

We establish a logarithmic Sobolev inequality for complete $C^{1,1}$ immersed submanifolds of dimension $m\ge2$ in Cartan--Hadamard manifolds with sectional curvature at most $-b^2$. The inequality retains the Euclidean sharp constant after subtraction of $(m-1)^2b^2$ from the Fisher and mean-curvature energy; this coefficient is maximal for a lower bound uniform over $b\ge0$. For immersed surfaces, we prove both a finite-domain critical exponential inequality and a global Ruf-type inequality with a positive $L^2$ term. Both have potential $|H|^2-b^2$, exponent $16π$ and an absolute multiplicative constant, and follow from one geometric heat-kernel comparison. The exponent and curvature coefficient are optimal. We classify Gaussian equality in the logarithmic inequality and geometric equality in the higher-dimensional Nash consequence. All inequality constants are independent of the codimension.