Limiting multiple hyperchargeless scalar triplets using electroweak phase transition and other constraints

TL;DR

This paper investigates how multiple scalar triplets with an O(N) symmetry can induce a strong electroweak phase transition while satisfying experimental and theoretical constraints, predicting a minimum of around 70 triplets.

Contribution

It provides a combined analysis of constraints on multiple scalar triplets, establishing a lower bound of approximately 70 triplets for a strong phase transition and compatibility with current data.

Findings

At least 70 scalar triplets are needed for a strong electroweak phase transition.

The model remains consistent with Higgs decay, dark matter detection, and Landau pole constraints.

Potential gravitational wave signals are identified in the viable parameter space.

Abstract

While an additional scalar multiplet over and above the Standard Model can lead to a strong electroweak phase transition, depending on its quantum numbers, it also potentially confronts crucial constraints from theory and experiments. Should there exist more than one copy of such a multiplet, it is possible to predict that number from the requirements of a strong electroweak phase transition and agreement with the latest constraints. We aim to probe this specific issue in this study in the context of $N$ degenerate scalar triplets governed by a global O$(N)$ symmetry. We fold in important constraints from $h \to \gamma\gamma$ signal strength, dark matter direct detection and Landau pole behaviour. A combined analysis reveals $N \gtrsim 70$ for a strong phase transition and consistency with the constraints. We also look into possible gravitational wave signals in the parameter regions of interest.