Abstract
It has long been known that the sharpened tension between the observed and inferred values of the Hubble constant can be alleviated if a fraction of dark-matter particles of type were produced nonthermally in association with photons through the decays of a heavy and relatively long-lived state, viz., . It was recently proposed that this model can also resolve the long-standing lithium (also known as ) problem if and , where and are, respectively, the masses of and . We confront this proposal with experiment and demonstrate that cold dark matter decaying before recombination cannot resolve the problem. Moreover, we show that the best-case scenario for alleviating the tension within the context of cold dark matter decaying before recombination arises when the particles decay exclusively into dark radiation, while leaving completely unmodified the production of light elements. To this end, we calculate the general functional form describing the number of equivalent light neutrino species carried by . We show that to resolve the tension at the level, a 55% correction in is needed and that the required is excluded at 95% C.L. by Planck data. We argue in favor of a more complex model of dynamical dark matter to relax the tension.
- Received 24 October 2020
- Accepted 22 January 2021
DOI:https://doi.org/10.1103/PhysRevD.103.035025
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