Relaxion fluctuations (self-stopping relaxion) and overview of relaxion stopping mechanisms

An Erratum to this article was published on 05 January 2021

This article has been updated


In implementations of the electroweak scale cosmological relaxation mechanism proposed so far, the effect of the quantum fluctuations of the homogeneous relaxion field has been ignored. We show that they can grow during the classical cosmological evolution of the relaxion field passing through its many potential barriers. The resulting production of relaxion particles can act as an efficient stopping mechanism for the relaxion. We revisit the original relaxion proposal and determine under which conditions inflation may no longer be needed as a source of friction. We review alternative stopping mechanisms and determine in detail the allowed parameter space for each of them (whether happening before, during and after inflation), also considering and severely constraining the case of friction from electroweak gauge boson production in models with large and Higgs-independent barriers.

A preprint version of the article is available at ArXiv.

Change history

  • 05 January 2021

    We correct a minor point in section 3.2 of “Relaxion Fluctuations (Self-stopping Relaxion) and Overview of Relaxion Stopping Mechanisms”, <Emphasis Type="Italic">JHEP</Emphasis> <Emphasis Type="Bold">05</Emphasis> (2020) 080. Furthermore, we clarify the origin of equation (4.25). Finally, we add some plots that are of interest.


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Correspondence to Enrico Morgante.

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ArXiv ePrint: 1911.08473

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Fonseca, N., Morgante, E., Sato, R. et al. Relaxion fluctuations (self-stopping relaxion) and overview of relaxion stopping mechanisms. J. High Energ. Phys. 2020, 80 (2020).

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  • Beyond Standard Model
  • Cosmology of Theories beyond the SM