In this book, a beautiful interplay between probability theory (Markov
processes, martingale theory) on the one hand and operator and spectral
theory on the other yields a uniform treatment of several kinds of
Hamiltonians such as the Laplace operator, relativistic Hamiltonian,
Laplace-Beltrami operator, and generators of Ornstein-Uhlenbeck
processes. The unified approach provides a new viewpoint of and a deeper
insight into the subject.