Constraints on Primordial Magnetic Fields from Inflation

Understand

We present generic bounds on magnetic fields produced from cosmic inflation.

• By investigating field bounds on the vector potential, we constrain both the quantum mechanical production of magnetic fields and their classical growth in a model independent way.
• For classical growth, we show that only if the reheating temperature is as low as T_{reh} <~ 10^2 MeV can magnetic fields of 10^{-15} G be produced on Mpc scales in the present universe.
• For purely quantum mechanical scenarios, even stronger constraints are derived.