Electroweak Vacuum (In)Stability in an Inflationary Universe

TL;DR

The paper investigates the instability of the electroweak vacuum during inflation, showing it can decay rapidly via Hawking-Moss transitions unless inflation occurs at very low energy scales, implying new physics might be needed for stability.

Contribution

It demonstrates that electroweak vacuum decay during inflation is more rapid than flat spacetime analysis suggests, especially via Hawking-Moss transitions, and links vacuum stability to inflationary parameters and new physics.

Findings

Electroweak vacuum decays via Hawking-Moss transition during inflation.

Low inflation rate ($H_{inf} \,\lesssim\, 10^9-10^{12}$ GeV) can prevent rapid decay.

Detection of tensor perturbations would suggest the need for new physics to stabilize the vacuum.

Abstract

Recent analysis shows that if the 125-126 GeV LHC resonance turns out to be the Standard Model Higgs boson, the electroweak vacuum would be a metastable state at 98% C.L. In this paper we argue that, during inflation, the electroweak vacuum can actually be very short-lived, contrary to the conclusion that follows from the flat spacetime analysis. Namely, in the case of a pure Higgs potential the electroweak vacuum decays via the Hawking-Moss transition, which has no flat spacetime analogue. As a result, the Higgs vacuum is unstable, unless the rate of inflation is low enough: $H_{\rm inf}\lesssim 10^9-10^{12}$ GeV. Models of inflation with such a low rate typically predict negligible tensor perturbations in the cosmic microwave background radiation (CMBR). This is also true for models in which the perturbations are produced by a curvaton field. We also find that if the effective curvature of the Higgs potential at a local maximum (which may be induced by inflaton-Higgs interactions) is large enough, then the decay of the electroweak vacuum is dominated by the Coleman-de Luccia transition. The electroweak vacuum is also short-lived in this case, due to a negative effective self-interaction coupling. Based on our analysis of Higgs vacuum stability during inflation, we conclude that the observation of tensor perturbations by the Planck satellite would provide strong indirect evidence for new physics beyond the Standard Model responsible for stabilisation of the electroweak vacuum.