Sharp exponential decay rates for anisotropically damped waves

TL;DR

This paper establishes conditions under which solutions to anisotropically damped wave equations on compact manifolds decay exponentially, providing explicit formulas for decay rates and constructing specific damping examples.

Contribution

It extends classical geometric control conditions to anisotropic damping, deriving explicit decay rate formulas and constructing concrete damping functions on flat tori.

Findings

Exponential energy decay under anisotropic geometric control and unique continuation.

Explicit formula for optimal decay rate in terms of spectral data.

Construction of anisotropic damping functions satisfying the conditions.

Abstract

In this article, we study energy decay of the damped wave equation on compact Riemannian manifolds where the damping coefficient is anisotropic and modeled by a pseudodifferential operator of order zero. We prove that the energy of solutions decays at an exponential rate if and only if the damping coefficient satisfies an anisotropic analogue of the classical geometric control condition, along with a unique continuation hypothesis. Furthermore, we compute an explicit formula for the optimal decay rate in terms of the spectral abscissa and the long-time averages of the principal symbol of the damping over geodesics, in analogy to the work of Lebeau for the isotropic case. We also construct genuinely anisotropic dampings which satisfy our hypotheses on the flat torus.