Primordial magnetic fields from a non-singular bouncing cosmology

Abstract

Although inflation is a natural candidate to generate the lengths of coherence of magnetic fields needed to explain current observations, it needs to break conformal invariance of electromagnetism to obtain significant magnetic amplitudes. Of the simplest realizations are the kinetically-coupled theories $f^2(\varphi )F_{\mu \nu }{F}^{\mu \nu }$ (or $IFF$ theories). However, these are known to suffer from electric fields backreaction or the strong coupling problem. In this work we shall confirm that such class of theories are problematic to support magnetogenesis during inflationary cosmology. On the contrary, we show that a bouncing cosmology with a contracting phase dominated by an equation of state with $p>-\rho /3$ can support magnetogenesis, evading the {backreaction/strong-coupling problem}. Finally, we study safe magnetogenesis in a particular bouncing model with an ekpyrotic-like contracting phase. In this case we found that $f^2(\varphi )F^2$-instabilities might arise during the final kinetic-driven expanding phase for steep ekpyrotic potentials.

33 pages, 7 figures, v2: references added, typos corrected, v3 Final version published in NPB

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• Generation of large-scale magnetic fields, non-Gaussianity, and primordial gravitational waves in inflationary cosmology
• Effective Theory of Inflationary Magnetogenesis and Constraints on Reheating
• Primordial Gravitational Waves Induced by Magnetic Fields in an Ekpyrotic Scenario
• Inflationary magneto-(non)genesis, increasing kinetic couplings, and the strong coupling problem
• Magnetogenesis in Matter - Ekpyrotic Bouncing Cosmology
• Cross-correlations between scalar perturbations and magnetic fields in bouncing universes
• Primordial Magnetogenesis in a Bouncing Universe
• Enhance Primordial Black Hole Abundance through the Non-linear Processes around Bounce Point
• Superhorizon magnetic fields
• Large-scale gauge spectra and pseudoscalar couplings
• Smooth magnetogenesis
• Revisiting primordial magnetic fields through 21-cm physics: Bounds and forecasts
• The hypermagnetic power spectra and the phases of Sakharov oscillations
• Primordial magnetogenesis in a bouncing model with dark energy
• Primordial magnetic non-Gaussianity with generic vacua and detection prospects in CMB spectral distortions
• Primordial Magnetic Field from Gravitationally Coupled Electrodynamics in Bouncing Scenario