On the Cauchy problem for microlocally symmetrizable hyperbolic systems with log-Lipschitz coefficients

TL;DR

This paper proves well-posedness for hyperbolic systems with log-Lipschitz coefficients, establishing energy estimates with finite derivative loss, and addresses the challenges posed by low regularity in coefficients and solutions.

Contribution

It introduces a framework for analyzing the Cauchy problem for hyperbolic systems with very low regularity coefficients, including energy estimates and well-posedness results.

Findings

Energy estimates with finite derivative loss are established.

Well-posedness in $H^$ is proved under certain smoothness conditions.

Local existence and uniqueness are derived from the main results.

Abstract

The present paper concerns the well-posedness of the Cauchy problem for microlocally symmetrizable hyperbolic systems whose coefficients and symmetrizer are log-Lipschitz continuous, uniformly in time and space variables. For the global in space problem we establish energy estimates with finite loss of derivatives, which is linearly increasing in time. This implies well-posedness in $H^\infty$, if the coefficients enjoy enough smoothness in $x$. From this result, by standard arguments (i.e. extension and convexification) we deduce also local existence and uniqueness. A huge part of the analysis is devoted to give an appropriate sense to the Cauchy problem, which is not evident a priori in our setting, due to the very low regularity of coefficients and solutions.