Journal of High Energy Physics

, 2016:93 | Cite as

Constraints on relaxion windows

  • Kiwoon Choi
  • Sang Hui Im
Open Access
Regular Article - Theoretical Physics


We examine the low energy phenomenology of the relaxion solution to the weak scale hierarchy problem. Assuming that the Hubble friction is responsible for a dissipation of the relaxion energy, we identify the cosmological relaxion window which corresponds to the parameter region compatible with a given value of the acceptable number of inflationary e-foldings. We then discuss a variety of observational constraints on the relaxion window, including those from astrophysical and cosmological considerations. We find that majority of the parameter space with a relaxion mass m ϕ ≳ 100 eV or a relaxion decay constant f ≲107GeV is excluded by existing constraints. There is an interesting parameter region with m ϕ ∼ 0.2 − 10 GeV and f ∼ few − 200 TeV, which is allowed by existing constraints, but can be probed soon by future beam dump experiments such as the SHiP experiment, or by improved EDM experiments.


Beyond Standard Model Cosmology of Theories beyond the SM Higgs Physics 


Open Access

This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.


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Copyright information

© The Author(s) 2016

Authors and Affiliations

  1. 1.Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS)DaejeonKorea
  2. 2.Bethe Center for Theoretical Physics and Physikalisches Institut der Universität BonnBonnGermany

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