Intermediate Optimal Gevrey Exponents Occur

Abstract

Hypoellipticity in Gevrey classes $G^s$ is characterized for a simple family of sums of squares of vector fields satisfying the bracket hypothesis, with analytic coefficients. It is shown that hypoellipticity holds if and only if $s$ is greater than or equal to an optimal exponent that may take on any rational value.

References in corpus (1)

• Analytic hypoellipticity in dimension two