Decay Preserving Operators and Stability of the Essential Spectrum
  We establish criteria for the stability of the essential spectrum for unbounded operators acting in Banach modules. The applications cover operators acting on sections of vector fiber bundles over non-smooth manifolds or locally compact abelian groups, in particular differential operators of any order with complex measurable coefficients on an euclidean space, singular Dirac operators, and Laplace-Beltrami operators on Riemannian manifolds with measurable metrics. 
Vladimir Georgescu and Sylvain Golenia