TY  - JOUR
AU  - Escudero, M.
AU  - Hooper, D.
AU  - Krnjaic, G.
AU  - Pierre, M.
PY  - 2019
DA  - 2019//
TI  - Cosmology with a very light Lmu – Ltau gauge boson
T2  - J. High Energy Phys.
JO  - Journal of High Energy Physics
SP  - 071
EP  - 29pp
VL  - 03
IS  - 3
PB  - Springer
KW  - Cosmology of Theories beyond the SM
KW  - Beyond Standard Model
KW  - Neutrino Physics
AB  - In this paper, we explore in detail the cosmological implications of an abelian L – L gauge extension of the Standard Model featuring a light and weakly coupled Z. Such a scenario is motivated by the longstanding approximate to 4 sigma discrepancy between the measured and predicted values of the muon's anomalous magnetic moment, (g – 2), as well as the tension between late and early time determinations of the Hubble constant. If sufficiently light, the Z population will decay to neutrinos, increasing the overall energy density of radiation and altering the expansion history of the early universe. We identify two distinct regions of parameter space in this model in which the Hubble tension can be significantly relaxed. The first of these is the previously identified region in which a approximate to 10 – 20 MeV Z reaches equilibrium in the early universe and then decays, heating the neutrino population and delaying the process of neutrino decoupling. For a coupling of g (-) similar or equal to (3 – 8) x 10(-4), such a particle can also explain the observed (g – 2) anomaly. In the second region, the Z is very light (mZ approximate to 1eV to MeV) and very weakly coupled (g (-) approximate to 10(-13) to 10(-9)). In this case, the Z population is produced through freeze-in, and decays to neutrinos after neutrino decoupling. Across large regions of parameter space, we predict a contribution to the energy density of radiation that can appreciably relax the reported Hubble tension, N-eff similar or equal to 0.2.
SN  - 1029-8479
UR  - https://arxiv.org/abs/1901.02010
UR  - https://doi.org/10.1007/JHEP03(2019)071
DO  - 10.1007/JHEP03(2019)071
LA  - English
N1  - WOS:000461295500006
ID  - Escudero_etal2019
ER  -