Universal upper limit on inflation energy scale from cosmic magnetic field

TL;DR

This paper establishes an upper limit on the inflation energy scale based on observed cosmic magnetic fields, highlighting potential conflicts with inflationary models if certain magnetic field strengths are confirmed.

Contribution

It derives a universal upper bound on the inflation energy scale from cosmic magnetic field observations within a broad class of models.

Findings

Upper bound on inflation energy scale: rho_{inf}^{1/4} < 2.5 x 10^{-7} M_{Pl} (B_{obs}/10^{-15}G)^{-2]

Constraint on tensor-to-scalar ratio: r < 10^{-19} (B_{obs}/10^{-15}G)^{-8]

Potential tension between inflationary magnetogenesis and future gravitational wave detections.

Abstract

Recently observational lower bounds on the strength of cosmic magnetic fields were reported, based on gamma-ray flux from distant blazars. If inflation is responsible for the generation of such magnetic fields then the inflation energy scale is bounded from above as rho_{inf}^{1/4} < 2.5 times 10^{-7}M_{Pl} times (B_{obs}/10^{-15}G)^{-2} in a wide class of inflationary magnetogenesis models, where B_{obs} is the observed strength of cosmic magnetic fields. The tensor-to-scalar ratio is correspondingly constrained as r< 10^{-19} times (B_{obs}/10^{-15}G)^{-8}. Therefore, if the reported strength B_{obs} \geq 10^{-15}G is confirmed and if any signatures of gravitational waves from inflation are detected in the near future, then our result indicates some tensions between inflationary magnetogenesis and observations.