An adiabatic approximation to the path integral for relativistic fermionic fields

A new approach to the path integral over fermionic fields, based on the extension of a reformulation of the adiabatic approximation to some quantum-mechanical systems, is presented. A novel non-analytic contribution to the effective fermionic action for a fermion field coupled to a non-Abelian vector field is identified. The possible interpretation of this contribution as a violation of the decoupling theorem in quantum field theory (QFT) is discussed. The generalization of the approach to the case of finite temperature and density suggests the possibility to apply it to the understanding of non-perturbative properties in QFT and their dependence on temperature and density.