Relaxion Dark Matter from Stochastic Misalignment

Abstract

Cosmological relaxation of the electroweak scale via Higgs-axion interplay, named as relaxion mechanism, provides a dynamical solution to the Higgs mass hierarchy. In the original proposal by Graham, Kaplan and Rajendran, the relaxion abundance today is too small to explain the dark matter of the universe because of the high suppression of the misalignment angle after inflation. It was then realised by Banerjee, Kim and Perez that reheating effects can displace the relaxion, thus enabling it to account for the dark matter abundance from the misalignment mechanism. However, this scenario is realised in a limited region of parameter space to avoid runaway. We show that in the regime where inflationary fluctuations dominate over the classical slow-roll, the "stochastic misalignment" of the field due to fluctuations can be large. We study the evolution of the relaxion after inflation, including the high-temperature scenario, in which the barriers of the potential shrink and destabilise temporarily the local minimum. We open new regions of parameter space where the relaxion can naturally explain the observed dark matter density in the universe, towards larger coupling, larger mass, larger mixing angle, smaller decay constant, as well as larger scale of inflation.

25 pages, 5 figures. v2: stellar bounds in figures 2,3,4 relaxed, rest unchanged

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Cited by in corpus (13)

• Stellar limits on scalars from electron-nucleus bremsstrahlung
• Probing an ultralight QCD axion with electromagnetic quadratic interaction
• Searching for dark matter with the Th-229 nuclear lineshape from laser spectroscopy
• Prospects of nuclear-coupled-dark-matter detection via correlation spectroscopy of I${}_2^{+}$ and Ca${}^{+}$
• On the sensitivity of nuclear clocks to new physics
• The Stochastic Relaxion
• Self-Gravity in Superradiance Clouds: Implications for Binary Dynamics and Observational Prospects
• Hierarchies from Landscape Probability Gradients and Critical Boundaries
• Oscillating nuclear charge radii as sensors for ultralight dark matter
• Plausible constraints and inflationary production for dark photons
• Emergent particles of de Sitter: thermal interpretation of the stochastic formalism and beyond
• Probing Quadratically Coupled Ultralight Dark Matter with Pulsar Timing Arrays
• Weak Scale Triggers in the SMEFT