Kernel estimates for the Weyl-H\"ormander calculus, Weak (1,1) boundedness and other regularity properties

Abstract

We provide kernel estimates for pseudo-differential operators in the $S(m,g)$ Weyl-H\"ormander calculus classes. These new results lead to boundedness theorems like the weak (1,1) type for these classes and the boundedness of these operators from Hardy spaces to Lebesgue spaces $L^p$. We prove that under a suitable hypoelliticity condition on the weigh $m,$ one can get the weak (1,1) inequality for the Fefferman order established previously by the second author in analogy to the classical $L^p$-boundedness theorem due to Fefferman. Our approach makes an extension to $S(m,g)$ classes of previous estimates proved by \'Alvarez and Hounie, Nagase, Kumano-Go, etc, for the H\"ormander classes including new regularity properties in this framework from the Hardy space $H^p$ to $L^p$ and also on Lorentz spaces. We have identified that the {\it Uniform H\"ormander Condition} plays a fundamental role in some of our boundedness theorems.