Duality and scale invariant magnetic fields from bouncing universes

Preprint number: CP3-Origins-2016-18 DNRF90 and DIAS-2016-18
Authors: Debika Chowdhury (Indian Institute of Technology Madras), Rajeev Kumar Jain (CP3-Origins), and L. Sriramkumar (Indian Institute of Technology Madras)
External link: arXiv.org

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 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. Finally, we show that the power spectrum of the magnetic field remains invariant under a two parameter family of transformations of the non-minimal coupling function.