2009 Volume 15 Issue 3 Pages 399-421
A scalar quantum field model defined on a pseudo Riemannian manifold is considered. The model is unitarily transformed to the one with a variable mass. By means of a Feynman-Kac-type formula, it is shown that when the variable mass is short range, the Hamiltonian has no ground state. Moreover the infrared divergence of the expectation values of the number of bosons in the ground state is discussed.