Electro-Weak Phase Transitions and Collider Signals in the Aligned 2-Higgs Doublet Model

TL;DR

This paper demonstrates that the Aligned 2-Higgs Doublet Model can produce strong electroweak phase transitions, generate detectable gravitational waves, and produce Higgs signals observable at the LHC, with testability at future experiments.

Contribution

It maps the parameter space of the A2HDM where electroweak phase transitions and collider signals coexist, linking gravitational wave and Higgs phenomenology.

Findings

A2HDM can produce strong first order electroweak phase transitions.

Both LISA and HL-LHC can test the model's predictions.

Parameter space links Higgs sector masses with observable signals.

Abstract

We show that the Aligned 2-Higgs Doublet Model (A2HDM) is a framework able to simultaneously accommodate strong first order electro-weak phase transitions, in turn generating detectable gravitational waves as well as a variety of Higgs boson signals (involving both the Standard Model state and its companions, both neutral and charged) accessible at the Large Hadron Collider (LHC). We map the corresponding expanse of parameter space where such a phenomenology is realised in terms of the relative values of the masses of the discovered Higgs boson and the extended Higgs sector states of this model: two neutral ones (a CP-even and a CP-odd) plus a pair of charged ones. We find that both the Laser Interferometer Space Antenna experiment and High-Luminosity LHC can test such a scenario within their lifetime. This study thus sets the stage for a two-prong complementary approach able to scrutinise the extended Higgs sector of the A2HDM in both its high and low temperature manifestations.