Naturalizing supersymmetry with a two-field relaxion mechanism

Abstract

We present a supersymmetric version of a two-field relaxion model that naturalizes tuned versions of supersymmetry. This arises from a relaxion mechanism that does not depend on QCD dynamics and where the relaxion potential barrier height is controlled by a second axion-like field. During the cosmological evolution, the relaxion rolls with a nonzero value that breaks supersymmetry and scans the soft supersymmetric mass terms. Electroweak symmetry is broken after the soft masses become of order the supersymmetric Higgs mass term and causes the relaxion to stop rolling for superpartner masses up to ∼ 10 9 GeV. This can explain the tuning in supersymmetric models, including split-SUSY models, while preserving the QCD axion solution to the strong CP problem. Besides predicting two very weakly-coupled axion-like particles, the supersymmetric spectrum may contain an extra Goldstino, which could be a viable dark matter candidate.

A dynamical weak scale from inflation

“…Models with n = 2 do not need to break electroweak symmetry in the new physics sector and can thus be decoupled to higher scales, but quantum corrections necessarily induce a barrier that prevents the relaxion from rolling. These initial barriers thus need to be relaxed by an additional scalar in a double-scanning mechanism [4,20].…”

“…We estimate this in the thin wall approximation as in Ref. [41] by the following probability for remaining in the false vacuum [42], 20) where β ≡ Γ/H 4 is a dimensionless measure of the tunnelling rate per unit volume [43],…”

Large field excursions from a few site relaxion model

“…We hope it is feasible to overcome this difficulty with clever model building; however, the details of this construction and the continuum limit thereof are beyond the scope of our paper and left for future work. For a supersymmetric version of a two-field relaxion model, see [32].…”

Very low scale Coleman-Weinberg inflation with nonminimal coupling

“…[25,26]. Finally, the recently proposed relaxion mechanism [27], as a solution to the hierarchy problem of Higgs boson by utilizing a slowly rolling scalar field in the context of inflationary cosmology, also requires a very long period and a very low energy scale of inflation for a phase transition by QCD(-like) strong dynamics to take place during inflation, not only in the minimal model [27][28][29] but also in some extended models [30][31][32][33]. (However, for other extensions where the relaxion mechanism can work at relatively high scale, see, e.g., Refs.…”