Gravitational Lensing of the Cosmic Neutrino Background

Abstract: We study gravitational lensing of the cosmic neutrino background. This signal is undetectable for the foreseeable future, but there is a rich trove of information available. At least some of the neutrinos from the early universe will be non-relativistic today, with a closer surface of last scattering (compared to the cosmic microwave background) and with larger angles of deflection. Lensing of massive neutrinos is strongly chromatic: both the amplitude of lensing and the cosmic time at which the potential is traversed depend on neutrino momentum, in principle giving access to our entire causal volume, not restricted to the light cone. As a concrete example, we focus on the case where the cosmic neutrino background would be strongly lensed when passing through halos of galaxy clusters and galaxies. We calculate the Einstein radius for cosmic neutrinos and investigate the impact of neutrino mass.