Relaxion: A Landscape Without Anthropics

Abstract

The relaxion mechanism provides a potentially elegant solution to the hierarchy problem without resorting to anthropic or other fine-tuning arguments. This mechanism introduces an axion-like field, dubbed the relaxion, whose expectation value determines the electroweak hierarchy as well as the QCD strong CP violating $\bar{\theta }$ parameter. During an inflationary period, the Higgs mass squared is selected to be negative and hierarchically small in a theory which is consistent with 't Hooft's technical naturalness criteria. However, in the original model proposed by Graham, Kaplan and Rajendran (2015), the relaxion does not solve the strong CP problem, and in fact contributes to it, as the coupling of the relaxion to the Higgs field and the introduction of a linear potential for the relaxion produces large strong CP violation. We resolve this tension by considering inflation with a Hubble scale which is above the QCD scale but below the weak scale, and estimating the Hubble temperature dependence of the axion mass. The relaxion potential is thus very different during inflation than it is today. We find that provided the inflationary Hubble scale is between the weak scale and about 3 GeV, the relaxion resolves the hierarchy, strong CP, and dark matter problems in a way that is technically natural.

updated with new section; similar to version to be published in Physical Review D

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Cited by in corpus (21)

• Inflating to the Weak Scale
• Higgs relaxation after inflation
• Relaxion and light (pseudo)scalars at the HL-LHC and lepton colliders
• The QCD Axion at Finite Density
• The Nelson-Barr Relaxion
• Collider searches of scalar singlets across lifetimes
• Higgs Criticality beyond the Standard Model
• Relaxion Dark Matter
• Runaway Relaxion from Finite Density
• From axion quality and naturalness problems to a high-quality ${\mathbb{Z}}_N$ QCD relaxion
• Relaxion Dark Matter from Stochastic Misalignment
• The Relaxion Measure Problem
• Paper-boat relaxion
• A warped relaxion
• Peccei-Quinn Relaxion
• The Stochastic Relaxion
• Cosmological Relaxation from Dark Fermion Production
• Light Higgs Boson from a Pole Attractor
• Gravitational tests of electroweak relaxation
• Hierarchies from Landscape Probability Gradients and Critical Boundaries
• Mixing Particle Production for Relaxion Mechanism