The Logarithmic Laplacian on Complete Riemannian Manifolds

Abstract

We introduce, for the first time, a Bochner representation of the logarithmic Laplacian on general complete Riemannian manifolds via spectral calculus and the heat semigroup. More precisely, letting $P_0=E(\{0\})$ denote the orthogonal projection onto $\ker (-\Delta )$ and $Q=I-P_0$, and defining the logarithmic operator to vanish on $\ker (-\Delta )$, we prove \[ \log(-Δ)f = \int_0^\infty \frac{e^{-t}Qf-e^{tΔ}Qf}{t}\,dt, \] where the integral converges in the strong improper sense in $L^2$. This representation recovers the classical pointwise logarithmic Laplacian on ${\mathbb{R}}^n$. Under a lower Ricci curvature bound and an explicit large-time heat-kernel integrability condition, we derive a pointwise integral representation on complete noncompact manifolds. We also compare the spectral and heat-kernel definitions and identify their difference explicitly in terms of the loss of heat mass. On ${\mathbb{H}}^n$, $n\ge 2$, we compute the fractional and logarithmic kernels, determine their asymptotics at zero and infinity, and derive absolute convergence, continuity, and $L^p$ integrability under Dini and weighted integrability assumptions.