Flavour Physics in two-Higgs-doublet models

TL;DR

This paper reviews various Two-Higgs-Doublet Models (2HDMs), focusing on their mechanisms to suppress flavour-changing neutral currents and analyzing their effects on key flavour observables.

Contribution

It compares three specific 2HDM implementations—discrete Z2-symmetry, minimal flavour violation, and Aligned 2HDM—highlighting their phenomenological differences in flavour physics.

Findings

All models eliminate tree-level FCNCs.

Different models predict distinct effects on B-meson decays.

Phenomenological differences are demonstrated in key flavour observables.

Abstract

Despite the tremendous success of the Standard Model, the arguments for the necessity of an extension are compelling. An attractive option is provided by Two-Higgs-Doublet models, due to their simplicity and them being the low-energy limit of some more complete theories. In the most general version of the model, the fermionic couplings of the neutral scalars are non-diagonal in flavour and, therefore, generate unwanted flavour-changing neutral-current phenomena. Different ways to suppress FCNCs have been developed, giving rise to a variety of specific implementations of the 2HDM. Three of these are discussed in this talk, comparing their phenomenological influence in flavour observables: The use of a discrete Z2-symmetry, an expansion around this limit in a minimal flavour violation scenario assuming the decoupling limit, and the Aligned Two-Higgs-Doublet Model. All of these result in the absence of tree-level flavour-changing neutral currents. Their different phenomenological consequences are demonstrated for a selection of observables, namely (semi-) leptonic decays, B->X_s gamma and mixing in the B0_d,s-systems.