Anisotropic non-singular quantum bounce as a seesaw and amplification mechanism for magnetic fields

Abstract: We investigate the evolution of a homogeneous magnetic field within Bianchi-I loop quantum cosmology, in which the big bang singularity is replaced with an anisotropic quantum bounce. Using effective spacetime description, we conduct extensive numerical simulations with randomized initial conditions for two cases: first in the presence of a pure homogeneous magnetic field and then adding a massless scalar field that effectively captures the bounce regime even in the presence of inflationary potentials. For a cigar-like approach to the classical big bang, which is far more prevalent than a point-like approach, the quantum geometric bounce acts as a seesaw mechanism for magnetic field energy density. Due to the seesaw mechanism, the magnetic field energy density gets amplified by several orders of magnitude across the bounce for a small pre-bounce value of magnetic field energy density, or vice versa. In the presence of the scalar field, the seesaw mechanism is completely replaced by amplification of the magnetic field across the bounce when the initial energy density of the scalar field significantly dominates. When the universe has a point-like approach to the classical big bang, the seesaw mechanism is absent, and magnetic field energy density experiences amplification or suppression across the non-singular bounce depending on initial densities.