[Paper Review] SuperCool Inflation: A Graceful Exit from Eternal Inflation at LHC Scales and Below

Douglas Spolyar|arXiv (Cornell University)|Nov 15, 2011

Cosmology and Gravitation Theories67 references3 citations

TL;DR

This paper proposes SuperCool Inflation (SCI), a mechanism for a graceful exit from eternal inflation using a thermal, technically natural process involving QCD-like fermions and a Yukawa-coupled inflaton. As the Universe cools, a frozen non-Abelian gauge group triggers a tadpole term that destabilizes the false vacuum, ending inflation without slow roll or scalar field dynamics, enabling testable inflation at LHC scales and generating CMB-compatible density perturbations via a light spectator aulos field.

ABSTRACT

In SuperCool Inflation (SCI), a technically natural and thermal effect gives a graceful exit to old inflation. The Universe starts off hot and trapped in a false vacuum. The Universe supercools and inflates solving the horizon and flatness problems. The inflaton couples to a set of QCD like fermions. When the fermions' non-Abelian gauge group freezes, the Yukawa terms generate a tadpole for the inflaton, which removes the barrier. Inflation ends, and the Universe rapidly reheats. The thermal effect is technically natural in the same way that the QCD scale is technically natural. In fact, Witten used a similar mechanism to drive the Electro-Weak (EW) phase transition; critically, no scalar field drives inflation, which allows SCI to avoid eternal inflation and the measure problem. SCI also works at scales, which can be probed in the lab, and could be connected to EW symmetry breaking. Finally, we introduce a light spectator field to generate density perturbations, which match the CMB. The light field does not affect the inflationary dynamics and can potentially generate non-Gaussianities and isocurvature perturbations observable with Planck.

Motivation & Objective

• To resolve the 'graceful exit' problem in old inflation, where tunneling is too slow to end inflation.
• To avoid eternal inflation and the associated measure problem by eliminating slow-roll dynamics.
• To enable inflation at low energy scales (TeV and below), making it testable at the LHC.
• To generate adiabatic density perturbations compatible with CMB observations without relying on the inflaton field.
• To introduce a new mechanism—'aulos'—for generating isocurvature and non-Gaussian perturbations via a pseudo-Nambu-Goldstone boson.

Proposed method

• The model uses a complex scalar inflaton field with a Coleman-Weinberg potential, coupled to QCD-like fermions via Yukawa interactions.
• Finite temperature effects stabilize the false vacuum during inflation, suppressing tunneling.
• At a critical temperature Tc, a non-Abelian gauge group freezes, generating a fermion condensate ⟨λ̄λ⟩ ≃ Tc³.
• This condensate induces a tadpole term in the inflaton potential, removing the barrier and ending inflation.
• A light spectator field (the 'aulos' field) is introduced as a pseudo-Nambu-Goldstone boson with a misalignment mechanism generating isocurvature perturbations.
• The aulos field oscillates at the end of inflation, decaying into radiation and producing adiabatic density perturbations matching CMB observations.

Experimental results

Research questions

• RQ1 Can a thermal, technically natural mechanism provide a graceful exit from eternal inflation without slow-roll dynamics?
• RQ2 Is it possible to achieve inflation at TeV-scale energies while avoiding the measure problem and trans-Planckian issues?
• RQ3 How can adiabatic density perturbations be generated without relying on the inflaton field?
• RQ4 Can the aulos mechanism produce observable non-Gaussianities and isocurvature perturbations detectable by Planck?
• RQ5 Does the Witten-type mechanism of vacuum destabilization via fermion condensates provide a viable alternative to scalar-driven inflation?

Key findings

• The model achieves a graceful exit from inflation via a thermal, technically natural tadpole mechanism triggered by a frozen non-Abelian gauge group.
• Inflation ends rapidly at Tc, avoiding eternal inflation and the associated measure problem, even though the false vacuum is classically stable.
• The mechanism is technically natural, analogous to the QCD scale, with a hierarchy of ~10^20 orders of magnitude, similar to the electroweak scale.
• The model operates at or below LHC energies, making it potentially testable in the laboratory.
• The aulos field generates isocurvature perturbations that evolve into adiabatic density perturbations consistent with CMB observations.
• The model predicts observable non-Gaussianities and isocurvature modes, potentially detectable by Planck and future CMB experiments.