Duality and scale invariant magnetic fields from bouncing universes

Understand

Recently, we had numerically shown that, for a non-minimal coupling that is a simple power of the scale factor, scale invariant magnetic fields arise in a class of bouncing universes.

• In this work, we {\it analytically} evaluate the spectrum of magnetic and electric fields generated in a sub-class of such models.
• We illustrate that, for cosmological scales which have wavenumbers much smaller than the wavenumber associated with the bounce, the shape of the spectrum is preserved across the bounce.
• Using the analytic solutions obtained, we also illustrate that the problem of backreaction is severe at the bounce.