A strong electroweak phase transition in the 2HDM after LHC8

TL;DR

This paper investigates the electroweak phase transition in the two-Higgs-doublet model, showing that a strong first-order transition favors specific scalar mass hierarchies and can enhance the Higgs to gamma gamma decay rate, consistent with recent LHC data.

Contribution

It provides a comprehensive parameter space analysis demonstrating conditions for a strong electroweak phase transition in the 2HDM, linking it to observable Higgs decay enhancements.

Findings

Strong first-order phase transition favors a light SM-like scalar and heavy pseudo-scalar.

Mass hierarchy in scalars: m_H^+ < m_H^0 < m_A^0 > 400 GeV.

Enhanced h^0 -> gamma gamma decay rate is compatible with a strong phase transition.

Abstract

The nature of the electroweak phase transition in two-Higgs-doublet models is revisited in light of the recent LHC results. A scan over an extensive region of their parameter space is performed, showing that a strongly first-order phase transition favours a light neutral scalar with SM-like properties, together with a heavy pseudo-scalar (m_A^0 > 400 GeV) and a mass hierarchy in the scalar sector, m_H^+ < m_H^0 < m_A^0. We also investigate the h^0 -> gamma gamma decay channel and find that an enhancement in the branching ratio is allowed, and in some cases even preferred, when a strongly first-order phase transition is required.