Quantum cosmological correlations in an inflating universe: Can fermion and gauge field loops give a scale-free spectrum?

This paper extends the calculation of quantum corrections to the cosmological correlation <zeta zeta >, which has been done by Weinberg for a loop of minimally coupled scalars, to other types of matter loops and a general and realistic potential. It is shown here that departures from scale invariance are never large even when Dirac, vector, and conformal scalar fields are present during inflation. No fine-tuning is needed, in the sense that effective masses or coupling constants can have arbitrary values. Even when the mass is as large as M-Pl, the one-loop result is still naturally smaller than the classical one. Thus, the results show that the existence of these fields during inflation may not be ruled out and is consistent with natural reheating.