Leptogenesis in cosmological relaxation with particle production

Minho Son,Tevong You,Fang Ye

doi:10.1103/physrevd.99.095016

Abstract

Cosmological relaxation of the electroweak scale is improved by using particle production to trap the relaxion. We combine leptogenesis with such a relaxion model that has no extremely small parameters or large e-foldings. Scanning happens after inflation--now allowed to be at a high scale--over a sub-Planckian relaxion field range for an $\mathcal{O}(100)$ TeV cut-off scale of new physics. Particle production by the relaxion also reheats the universe and generates the baryonic matter-antimatter asymmetry. We propose a realisation in which out-of-equilibrium leptons, produced by the relaxion, scatter with the thermal bath through interactions that violate CP and lepton number via higher-dimensional operators. Such a minimal effective field theory setup, with no new physics below the cut-off, naturally decouples new physics while linking leptogenesis to relaxion particle production; the baryon asymmetry of the universe can thus be intrinsically tied to a weak scale hierarchy.

Highlights

Cosmological relaxation of the electroweak scale [1] has gained much interest in recent years as an alternative approach to the hierarchy problem that allows decoupled new physics without fine-tuning the Higgs mass
Such a minimal effective field theory setup, with no new physics below the cutoff, naturally decouples new physics while linking leptogenesis to relaxion particle production; the baryon asymmetry of the universe can be intrinsically tied to a weak scale hierarchy
The light neutrino mass bound mν ∼ 0.1 eV implies that the corresponding operator scale is Λ5 ∼ 1014 GeV for an Oð1Þ Wilson coefficient cð5Þ. The contribution of this operator to the baryon asymmetry is typically negligible for the low reheating temperatures of the relaxion, and we focus on dimension-7, lepton-number-violating operators generated at a scale Λ7

Summary

INTRODUCTION

Cosmological relaxation of the electroweak scale [1] has gained much interest in recent years as an alternative approach to the hierarchy problem that allows decoupled new physics without fine-tuning the Higgs mass. In the original GKR mechanism [1], the trapping backreaction acted on the relaxion’s periodic potential, VðφÞ ⊃ Λ4c cosðφ=fpÞ; ð2Þ whose barriers Λ4c ≃ Λ3QCDv will grow with a linear dependence on v until they are sufficiently large to compensate for the slope. This creates several problems: if φ is the QCD axion, it no longer solves the strong CP problem without some additional mechanism, and if the periodic potential is due to the condensate of another gauge group, it reintroduces new physics near the weak scale. After describing the essential features of the HMT model we show how it can be combined in a natural way with leptogenesis during reheating

COSMOLOGICAL RELAXATION WITH PARTICLE PRODUCTION

LEPTOGENESIS

CONCLUSION

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