https://doi.org/10.1140/epjc/s10052-022-10518-3
Regular Article - Theoretical Physics
Weaker yet again: mass spectrum-consistent cosmological constraints on the neutrino lifetime
1
Sydney Consortium for Particle Physics and Cosmology, School of Physics, The University of New South Wales, 2052, Sydney, NSW, Australia
2
Centre for Cosmology, Particle Physics and Phenomenology, Université catholique de Louvain, Chemin du cyclotron, 2, 1348, Louvain-la-Neuve, Belgium
Received:
25
March
2022
Accepted:
11
June
2022
Published online:
25
July
2022
We consider invisible neutrino decay 
in the ultra-relativistic limit and compute the neutrino anisotropy loss rate relevant for the cosmic microwave background (CMB) anisotropies. Improving on our previous work which assumed massless
and 
, we reinstate in this work the daughter neutrino mass 
in a manner consistent with the experimentally determined neutrino mass splittings. We find that a nonzero introduces a new phase space factor in the loss rate 
proportional to 
in the limit of a small squared mass gap between the parent and daughter neutrinos, i.e., 
, where 
is the 
rest-frame lifetime. Using a general form of this result, we update the limit on using the Planck 2018 CMB data. We find that for a parent neutrino of mass 
eV, the new phase space factor weakens the constraint on its lifetime by up to a factor of 50 if 
corresponds to the atmospheric mass gap and up to 
if the solar mass gap, in comparison with naïve estimates that assume 
. The revised constraints are (i) 
s and 
s if only one neutrino decays to a daughter neutrino separated by, respectively, the atmospheric and the solar mass gap, and (ii) 
s in the case of two decay channels with one near-common atmospheric mass gap. In contrast to previous, naïve limits which scale as 
, these mass spectrum-consistent constraints are remarkably independent of the parent mass and open up a swath of parameter space within the projected reach of IceCube and other neutrino telescopes in the next two decades.
© The Author(s) 2022
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Funded by SCOAP3. SCOAP3 supports the goals of the International Year of Basic Sciences for Sustainable Development.
