Expanding the joint spectrum of pairs of commuting contractions

Abstract

We present a connection between solving the invariant subspace problem for a single operator  T T on Hilbert space and the existence of a common invariant subspace for two commuting related operators. In particular, we reduce the problem of the existence of nontrivial invariant subspaces for a single contraction with spectral radius one to the problem of the existence of common nontrivial invariant subspaces for a pair of commuting contractions with large joint spectra.