Radiatively induced Lorentz and CPT violation in Schwinger constant field approximation

The Schwinger proper-time method is an effective calculation method, explic itly gauge-invariant and nonperturbative. We make use of this method to inv estigate the radiatively induced Lorentz- and CPT-violating effects in quan tum electrodynamics when an axial-vector interaction term is introduced in the fermionic sector. The induced Lorentz- and CPT-violating Chern-Simons t erm coincides with the one obtained using a covariant derivative expansion but differs from the result usually obtained in other regularization scheme s. A possible ambiguity in the approach is also discussed. (C) 2001 Publish ed by Elsevier Science B.V.