[Paper Review] Relaxed Inflation

Walter Tangarife, Kohsaku Tobioka+2 more|arXiv (Cornell University)|Jun 1, 2017

Cosmology and Gravitation Theories4 citations

TL;DR

This paper proposes a relaxed inflation model where the inflaton acts as a relaxion that dynamically sets the Higgs mass to the weak scale. Inflation is driven by a shallow potential slope, followed by reheating via non-perturbative gauge-boson production and Schwinger pair creation, with Higgs mass relaxation occurring post-reheating, allowing the effective model cutoff near the Planck scale while evading phenomenological bounds.

ABSTRACT

We present an effective model where the inflaton is a relaxion that scans the Higgs mass and sets it at the weak scale. The dynamics consist of a long epoch in which inflation is due to the shallow slope of the potential, followed by a few number of e-folds where slow-roll is maintained thanks to dissipation via non-perturbative gauge-boson production. The same gauge bosons give rise to a strong electric field that triggers the production of electron-positron pairs via the Schwinger mechanism. The subsequent thermalization of these particles provides a novel mechanism of reheating. The relaxation of the Higgs mass occurs after reheating, when the inflaton/relaxion stops on a local minimum of the potential. We argue that this scenario may evade phenomenological and astrophysical bounds while allowing for the cutoff of the effective model to be close to the Planck scale. This framework provides an intriguing connection between inflation and the hierarchy problem.

Motivation & Objective

• To address the hierarchy problem by dynamically generating the weak scale via a relaxion mechanism during inflation.
• To reconcile inflation with the electroweak scale without fine-tuning.
• To propose a reheating mechanism driven by strong electric fields and Schwinger pair production.
• To ensure the effective field theory cutoff remains close to the Planck scale while satisfying observational and phenomenological constraints.

Proposed method

• The inflaton is identified as a relaxion that scans the Higgs mass through a potential with a shallow slope during inflation.
• Inflation proceeds via slow-roll on this shallow potential, sustained by dissipation from non-perturbative gauge-boson production.
• The gauge-boson production generates a strong electric field that triggers electron-positron pair creation via the Schwinger mechanism.
• Thermalization of the produced pairs provides a novel reheating mechanism, transitioning the universe to a hot plasma.
• After reheating, the relaxion settles into a local minimum, dynamically fixing the Higgs mass at the weak scale.
• The model is constructed to remain consistent with astrophysical and phenomenological bounds despite a high cutoff near the Planck scale.

Experimental results

Research questions

• RQ1 Can the relaxion mechanism be embedded within an inflationary framework without violating observational constraints?
• RQ2 How can reheating occur efficiently in a relaxion-driven inflation model?
• RQ3 What role does the Schwinger mechanism play in thermalizing the plasma after inflation?
• RQ4 Can the cutoff of the effective theory be near the Planck scale while remaining viable?
• RQ5 Does the post-reheating relaxation of the Higgs mass remain consistent with low-energy phenomenology?

Key findings

• The model achieves inflation through a shallow potential slope, with the inflaton's dynamics driven by dissipation from non-perturbative gauge-boson production.
• Reheating is realized via Schwinger pair production of electron-positron pairs, followed by thermalization of the plasma.
• The Higgs mass is dynamically relaxed to the weak scale after reheating, when the relaxion settles into a local minimum.
• The effective field theory cutoff can be close to the Planck scale without violating current phenomenological or astrophysical bounds.
• The framework provides a unified mechanism linking inflation and the hierarchy problem through the relaxion's dual role in inflation and electroweak scale generation.