https://doi.org/10.1140/epjc/s10052-024-12963-8
Regular Article - Theoretical Physics
Revisiting big bang nucleosynthesis with a new particle species: effect of co-annihilation with nucleons
School of Physical Sciences, Indian Association for the Cultivation of Science, 2A and 2B Raja S.C. Mullick Road, 700 032, Kolkata, India
Received:
30
November
2023
Accepted:
26
May
2024
Published online:
21
June
2024
In big bang nucleosynthesis (BBN), the light matter abundance is dictated by the neutron-to-proton (n/p) ratio which is controlled by the standard weak processes in the early universe. Here, we study the effect of an extra particle species (
) which co-annihilates with neutron (proton), thereby potentially changing the (n/p) ratio in addition to the former processes. We find a novel interplay between the co-annihilation and the weak interaction in deciding the (n/p) ratio and the yield of . Large co-annihilation strength (
) in comparison to the weak coupling (
), potentially can alter the number of nucleons in the thermal bath modifying the (n/p) ratio from its standard evolution. We find that the standard BBN prediction is restored for 
, while the mass of being much smaller than the neutron mass. When the mass of is comparable to the neutron mass, we can allow large 
values, as the thermal abundance of becomes Boltzmann-suppressed. Therefore, the (n/p) ratio is restored to its standard value via dominant weak processes in later epochs. We also discuss the stability of the new particle in an effective theory framework for co-annihilation. Further, the co-annihilation interaction generates elastic scattering of and nucleons at the next-to-leading order. This provides a way to probe the scenario in direct detection experiments, if is accidentally stable over cosmological timescale.
© The Author(s) 2024
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.
