8,598 research outputs found
A Fresh Look at keV Sterile Neutrino Dark Matter from Frozen-In Scalars
Sterile neutrinos with a mass of a few keV can serve as cosmological warm
dark matter. We study the production of keV sterile neutrinos in the early
universe from the decay of a frozen-in scalar. Previous studies focused on
heavy frozen-in scalars with masses above the Higgs mass leading to a hot
spectrum for sterile neutrinos with masses below 8-10 keV. Motivated by the
recent hints for an X-ray line at 3.55 keV, we extend the analysis to lighter
frozen-in scalars, which allow for a cooler spectrum. Below the electroweak
phase transition, several qualitatively new channels start contributing. The
most important ones are annihilation into electroweak vector bosons,
particularly W-bosons as well as Higgs decay into pairs of frozen-in scalars
when kinematically allowed.Comment: 19 pages, 4 figures, model section (sec. 2) splits in effective
description (sec. 2) and UV completion (sec. 5), minor changes, references
added, matches published versio
Lower Bounds on U_{e3}
We give minimal values for the smallest lepton mixing parameter U_{e3},
applying 2-loop renormalization group equations in an effective theory
approach. This is relevant in scenarios that predict an inverted neutrino mass
spectrum with the smallest mass and U_{e3} being zero at tree level, a
situation known to be preserved at 1-loop order. At 2-loop, U_{e3} is generated
at a level of 10^{-12}-10^{-14}. Such small values are of interest in supernova
physics. Corresponding limits for the normal mass ordering are several orders
of magnitude larger. Our results show that U_{e3} can in general expected be to
be non-zero.Comment: 5 pages, 2 figures. Matches published versio
- …