Banach Algebras of Pseudodifferential Operators and Their Almost Diagonalization

We define new symbol classes for pseudodifferential operators and investigate their pseudodifferential calculus. The symbol classes are parametrized by commutative convolution algebras. To every solid convolution algebraA over a lattice Λ we associate a symbol class M. Then every operator with a symbol in M is almost diagonal with respect to special wave packets (coherent states or Gabor frames), and the rate of almost diagonalization is described precisely by the underlying convolution algebra A. Furthermore, the corresponding class of pseudodifferential operators is a Banach algebra of bounded operators on L(R). If a version of Wiener’s lemma holds for A, then the algebra of pseudodifferential operators is closed under inversion. The theory contains as a special case the fundamental results about Sjöstrand’s class and yields a new proof of a theorem of Beals about the Hörmander class S 0,0.