From Cosmic Bounces to Primordial Black Holes: The Role of Primordial Magnetic Fields
This work investigates how primordial magnetic fields generated during a contracting phase in a non-singular ekpyrotic bounce source curvature perturbations and influence subsequent primordial black hole formation. The study shows that these magnetic fields, amplified by time-dependent couplings, create an anisotropic stress that sources curvature perturbations. Using both monochromatic and critical collapse formalisms, the authors constrain the background cosmology to limit PBH dark matter fraction to $10^{-5}$ for benchmark parameters.