Boundedness for Gevrey and Gelfand-Shilov kernels to positive operators
  We study properties of positive operators on Gelfand-Shilov spaces, and distributions which are positive with respect to non-commutative convolutions. We prove that boundedness of kernels $K \in \maclD_s^{\prime}$ to positive operators, are completely determined by the behaviour of $K$ alone the diagonal. We also prove that positive elements $a$ in $\mascS^{\prime}$ with respect to twisted convolutions, having Gevrey class property of order $s\geq 1/2$ at the origin, then $a$ belongs to the Gelfand-Shilov space $\maclS_s$. 
Yuanyuan Chen and Joachim Toft
math.FA