2023/09/03 by Kento Asai, Asai, Kento, Tomoya Asano +5
Physics and Astronomy · #Particle physics theoretical and experimental studies #Cosmology and Gravitation Theories #Black Holes and Theoretical Physics
paper · pdf · doi:10.48550/arxiv.2309.01162
In this paper, we analyze parameter regions that can alleviate the Hubble tension in the U(1)Lμ- Lτ model with the broken lepton number U(1)L symmetry. As new particles, this model has a U(1)Lμ- Lτ gauge boson Z' and a Majoron ϕ, which can affect the early universe and the effective number of neutrino species N\rm eff. If Z' and ϕ simultaneously exist in the early universe, Z' - ϕ interaction processes such as Z'να↔ ϕνβ occur. The comparison of N\rm eff between the cases with and without the Z' - ϕ interaction processes shows that these processes make a small contribution of O(10-4) to N\rm eff, and it does not need to be considered for the alleviation of the Hubble tension. Based on these facts, we calculated N\rm eff for various Majoron parameters without the Z' - ϕ interaction processes to search parameters that could alleviate the Hubble tension. As a result, we found that the U(1)Lμ- Lτ gauge boson and Majoron can alleviate the Hubble tension in some parameter regions, and there is a non-trivial synergy contribution between Z' and ϕ. Moreover, the parameter region with a lighter mass mϕ\lesssim 2 MeV and a larger coupling λ\gtrsim 10-8 is excluded because it predicts too large N\rm eff, i.e. N\rm eff \gtrsim 3.5. The favored and restricted regions of the Majoron parameters depend on the Z' parameters because of the presence of the Z' contribution and synergy one.