2023/10/20 by Shao-Ping Li, Li, Shao-Ping, Bingrong Yu +1
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #Dark Matter and Cosmic Phenomena #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #Particle physics theoretical and experimental studies
paper · pdf · doi:10.48550/arxiv.2310.13492
openalex publication_date 2023/10/20 · openalex created_date 2023/10/24 · openalex updated_date 2026/07/28
A singlet majoron can arise from the seesaw framework as a pseudo-Goldstone boson when the heavy Majorana neutrinos acquire masses via the spontaneous breaking of global \rm U(1)L symmetry. The resulting cosmological impacts are usually derived from the effective majoron-neutrino interaction, and the majoron abundance is accumulated through the freeze-in neutrino coalescence. However, a primordial majoron abundance can be predicted in a minimal setup and lead to distinctive cosmological effects. In this work, we consider such a primordial majoron abundance from relativistic freeze-out and calculate the modification to the effective neutrino number N\rm eff. We demonstrate that the measurements of N\rm eff will constrain the parameter space from a primordial majoron abundance in an opposite direction to that from neutrino coalescence. When the contributions from both the primordial abundance and the freeze-in production coexist, the \rm U(1)L-breaking scale (seesaw scale) f will be pushed into a ''sandwiched window''. Remarkably, for majoron masses below 1 MeV and above the eV scale, the future CMB-S4 experiment will completely close such a low-scale seesaw window for f∈ [1,105]~\rm GeV. We highlight that any new light particle with a primordial abundance that couples to SM particles may lead to a similar sandwiched window, and such a general phenomenon deserves careful investigation.