  This paper studies the one-loop expansion of the amplitudes of
electromagnetism about flat Euclidean backgrounds bounded by a 3-sphere,
recently considered in perturbative quantum cosmology, by using zeta-function
regularization. For a specific choice of gauge-averaging functional, the
contributions to the full zeta value owed to physical degrees of freedom,
decoupled gauge mode, coupled gauge modes and Faddeev-Popov ghost field are
derived in detail, and alternative choices for such a functional are also
studied. This analysis enables one to get a better understanding of different
quantization techniques for gauge fields and gravitation in the presence of
boundaries.
