Symbol calculus and zeta-function regularized determinants

In this work, we use semigroup integral to evaluate zeta-function regularized determinants. This is especially powerful for nonpositive operators such as the Dirac operator. In order to understand fully the quantum effective action, one should know not only the potential term but also the leading kinetic term. In this purpose, we use the Weyl type of symbol calculus to evaluate the determinant as a derivative expansion. The technique is applied both to a spin-0 bosonic operator and to the Dirac operator coupled to a scalar field. (c) 2007 American Institute of Physics.