Gravitational Footprints of the A4-symmetric Three-Higgs-Doublet Model

Ricardo Jorge Dias Santos

Key information

Authors:

Ricardo Jorge Dias Santos (Ricardo Jorge Dias Santos)

Supervisors:

António de Aguiar e Pestana de Morais; Filipe Rafael Joaquim (Filipe Rafael Joaquim)

Published in

December 7, 2022

Abstract

Despite its great successes, the Standard Model of particle physics still leaves some questions unanswered, namely the origin of the baryon asymmetry of the Universe and neutrino oscillations. Therefore, the theory is incomplete. Several extensions of the Standard Model have been studied in the past few decades. Multi-Higgs-Doublets models have become popular as they provide ingredients for Electroweak Baryogenesis and seesaw mechanisms. With Beyond the Standard Models reaching the testing limits of current experiments, stochastic gravitational-wave backgrounds from cosmological phase transitions are being investigated as a novel testing approach. In this thesis, we study a three Higgs-doublets model with an A4 flavour symmetry, in the context of stochastic gravitational-wave backgrounds. Particularly, we consider the case where all three doublets acquire a real vacuum expectation value. Regarding Yukawa interactions, we assign the triplet representation of A4 to doublets of SU(2)L and different singlet representations of A4 to singlets of SU(2)L. After building the effective potential at finite temperatures, we implemented the latter in the widely used tool CosmoTransitions. Allowing new scalar bosons to have masses up to 400GeV, we found several first-order phase transitions with couplings smaller than 4 that lead to stochastic gravitational-wave backgrounds within the sensitivity of LISA, DECIGO and BBO. We also concluded that larger masses of new bosons lead to larger peak amplitudes of the stochastic gravitational-wave background spectrum. Particularly, detectable spectra require at least one new scalar boson heavier than 270-280GeV, hence heavier than the Higgs boson.