Cosmology with a very light Lμ − Lτ gauge boson

By Miguel Escudero, D. Hooper, G. Krnjaic, M. Pierre. Journal of High Energy Physics, 2019

193 citations recorded by the source corpus.

A bstractIn this paper, we explore in detail the cosmological implications of an abelian Lμ − Lτ gauge extension of the Standard Model featuring a light and weakly coupled Z′. Such a scenario is motivated by the longstanding ∼ 4σ discrepancy between the measured and predicted values of the muon’s anomalous magnetic moment, (g − 2)μ, 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 ∼ 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 gμ − τ ≃ (3 − 8) × 10−4, such a particle can also explain the observed (g − 2)μ anomaly. In the second region, the Z′ is very light (mZ′$$ {m}_{Z^{\prime }} $$ ∼ 1eV to MeV) and very weakly coupled (gμ − τ ∼ 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, ΔNeff ≃ 0.2.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/90af566cef03f4de1de8dcc56f61d4ce740c8d14

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Citations in the corpus

Precision early universe thermodynamics made simple: Neff and neutrino decoupling in the Standard Model and beyond (2020, methodology): “We note that the method has already been applied to study: i) the BBN effect of MeV-scale thermal dark sectors [1, 72], ii) the impact on BBN of invisible neutrino decays [71], iii) the cosmological consequences of light and weakly coupled flavorful gauge bosons [73], iv) Neff constraints on dark ph”
New physics in light of the H0 tension: An alternative view (2019, background): “One example of such model which also predicts a rather specific value of Neff is the abelian Lμ−Lτ extension of the Standard Model studied in [344], which predicts Neff ≈ 3.”
Refined bounds on MeV-scale thermal dark sectors from BBN and the CMB (2019, background): “Searches for light BSM species are not only carried out in terrestrial experiments, but a variety of astrophysical [71–76] and cosmological [77–84] constraints have been also derived on states with masses at the MeV scale.”
Neutrino non-standard interactions: A status report (2019, unknown): “It is also easy to connect this model to RK experimental anomalies in the flavour sector [342], and to discrepancies in the Hubble expansion rate measurement [343].”
Neutrino decoupling beyond the Standard Model: CMB constraints on the Dark Matter mass with a fast and precise Neff evaluation (2018, unknown): “Finally, we note that the possibilities of our simplified approach to neutrino decoupling are countless given the variety of extensions of the Standard Model with massless or light particles (for instance, see [87]).”
Muonic Boson Limits: Supernova Redux (2021, unknown): “[95], although in that case the limit extends”