Abstract
The Hubble parameter inferred from cosmic microwave background observations is consistently lower than that from local measurements, which could hint towards new physics. Solutions to the Hubble tension typically require a sizable amount of extra radiation during recombination. However, the amount of in the early Universe is unavoidably constrained by big bang nucleosynthesis (BBN), which causes problems for such solutions. We present a possibility to evade this problem by introducing neutrino self-interactions via a simple Majoron-like coupling. The scalar is slightly heavier than 1 MeV and allowed to be fully thermalized throughout the BBN era. The rise of neutrino temperature due to the entropy transfer via reactions compensates for the effect of a large on BBN. Values of as large as 0.7 are in this case compatible with BBN. We perform a fit to the parameter space of the model.
- Received 22 February 2021
- Accepted 6 May 2021
DOI:https://doi.org/10.1103/PhysRevD.103.123007
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.
Published by the American Physical Society