Quantum Cosmological Correlations in an Inflating Universe: Can fermion and gauge fields loops give a scale free spectrum?

TL;DR

This paper investigates quantum loop corrections from fermion and gauge fields during inflation, showing they do not significantly alter the scale invariance of the primordial spectrum, thus supporting their possible presence in the early universe.

Contribution

It extends previous calculations of quantum corrections to include fermion, gauge, and conformal scalar fields, demonstrating their minimal impact on scale invariance during inflation.

Findings

Quantum corrections remain small even with large field masses.

No fine tuning needed for coupling constants or masses.

Presence of these fields during inflation is consistent with observations.

Abstract

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 \emph{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 \emph{during} inflation may not be ruled out and is consistent with natural reheating.