Early Cosmological Axion Production Models Reconsidered

by Tommy on 4/05/2017

There is still considerable resistance to the axion hypothesis in the string theory community.


Axions, Instantons, and the Lattice, Michael Dine, Patrick Draper, Laurel Stephenson-Haskins and Di Xu (1 May 2017)

If the QCD axion is a significant component of dark matter, and if the universe was once hotter than a few hundred MeV, the axion relic abundance depends on the function χ(T), the temperature-dependent topological susceptibility. Uncertainties in this quantity induce uncertainties in the axion mass as a function of the relic density, or vice versa. At high temperatures, theoretical uncertainties enter through the dilute instanton gas computation, while in the intermediate and strong coupling regime, only lattice QCD can determine χ(T) precisely. We reassess the uncertainty on the instanton contribution, arguing that it amounts to less than a factor of 20 in χ at T = 1.5 GeV. We then combine the instanton uncertainty with a range of models for χ(T) at intermediate temperatures and determine the impact on the axion relic density. We find that for a given relic density and initial misalignment angle, the combined uncertainty amounts to a factor of 2-3 in the zero-temperature axion mass.

I’ll be the first to admit there may be an axion mass distribution with a long low mass tail.

So they can flail around all they want with this.


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