Cosmological constraint on vector mediator of neutrino-electron interaction in light of XENON1T excess

• Main Authors: Masahiro Ibe, Shin Kobayashi, Yuhei Nakayama, Satoshi Shirai
• Format: Article
• Language: English
• Published: SpringerOpen 2020-12-01
• Series: Journal of High Energy Physics
• Subjects: Beyond Standard Model; Cosmology of Theories beyond the SM
• Online Access: https://doi.org/10.1007/JHEP12(2020)004

Abstract Recently, the XENON1T collaboration reported an excess in the electron recoil energy spectrum. One of the simplest new physics interpretation is a new neutrino-electron interaction mediated by a light vector particle. However, for the parameter region favored by this excess, the constraints from the stellar cooling are severe. Still, there are astrophysical uncertainties on those constraints. In this paper, we discuss the constraint on the light mediator from the effective number of neutrino N eff in the CMB era, which provides an independent constraint. We show that N eff is significantly enhanced and exceeds the current constraint in the parameter region favored for the XENON1T excess. As a result, the interpretation by a light mediator heavier than about 1 eV is excluded by the N eff constraint.