Global Electroweak Symmetric Vacuum

TL;DR

This paper explores a scenario where the Standard Model's electroweak vacuum is metastable with an alternative global vacuum, involving Higgs-portal scalars, and discusses its implications for collider experiments and cosmology.

Contribution

It introduces a model with Higgs-portal couplings to singlet scalars with large N symmetry, demonstrating a long-lived metastable vacuum with potential observable signatures.

Findings

The current vacuum can be metastable with suppressed tunneling rates.

Order-one modifications to Higgs self-couplings are predicted.

Large contributions to off-shell Higgs invisible decay signals.

Abstract

Although the Higgs potential in the Standard Model (SM) contains only a simple electroweak symmetry breaking vacuum in the small field region, additional metastable or global vacua could exist in models beyond the SM. In this paper, we study one intriguing scenario with an additional electroweak symmetric vacuum that could be the global one. For the thermal universe ending at the current metastable vacuum, the electroweak symmetry should stay non-restored at high temperatures. We realize the scenario in a model with Higgs-portal couplings to SM singlet scalars with approximately global O(N) symmetries with a large N. For a large portion of model parameter space, both the quantum and thermal tunneling rates are suppressed such that our current metastable vacuum is long-lived enough. Our scenario predicts order-one changes for the Higgs self-couplings and a large contribution to the signal of the off-shell Higgs invisible decay. It can be partly probed at the LHC Run 3 and well tested at the high luminosity LHC. We also discuss the subcritical (anti-de Sitter) bubbles from the thermal tunneling that could have a large population and interesting cosmological implications.