KIPAC Tea Talk: Primordial Magnetic fields and modified recombination histories

Schiff Abstract: Perhaps the most significant challenge to the widely successful Lambda-CDM theory is the disagreement between late and early Universe measurements of the present day Hubble expansion rate (H0), referred to as the Hubble tension. One of the ways to resolve the Hubble tension is to modify the recombination history of the early universe. An intriguing proposal to realize this invokes primordial magnetic fields (PMFs) to stir up the plasma on small scales and speed up recombination. An earlier recombination shrinks the sound horizon at the surface of last scattering and consequently increases the early Universe inference of H0. On the small scales at which PMFs introduce baryon clumping, the nonlocal transport of photons in the Lyman-alpha resonance and Lyman-continuum, which mediate the recombination process, becomes important. Utilizing a linearized scheme for magnetohydrodynamics in the early Universe, our work provides a self-consistent and computationally inexpensive treatment of the evolution of PMF-induced small-scale inhomogeneities from magnetogensis to and through Recombination incorporating nonlocal radiative transport.