Anarchic Yukawas and top partial compositeness: the flavour of a successful marriage

TL;DR

This paper proposes a novel flavor model where the top quark's mass arises from partial compositeness in composite Higgs models, avoiding flavor constraints without flavor symmetries, and explains the down-type quark hierarchy dynamically.

Contribution

It introduces a new class of flavor models with high flavor scale and partial compositeness for the top, avoiding flavor constraints without flavor symmetries, and provides explicit realizations.

Findings

Flavor constraints are satisfied without flavor symmetries in minimal models.

Partial compositeness explains the bottom quark hierarchy dynamically.

The framework generalizes to larger cosets and representations.

Abstract

The top quark can be naturally singled out from other fermions in the Standard Model due to its large mass, of the order of the electroweak scale. We follow this reasoning in models of pseudo Nambu Goldstone Boson composite Higgs, which may derive from an underlying confining dynamics. We consider a new class of flavour models, where the top quark obtains its mass via partial compositeness, while the lighter fermions acquire their masses by a deformation of the dynamics generated at a high flavour scale. One interesting feature of such scenario is that it can avoid all the flavour constraints without the need of flavour symmetries, since the flavour scale can be pushed high enough. We show that both flavour conserving and violating constraints can be satisfied with top partial compositeness without invoking any flavour symmetry for the up-type sector, in the case of the minimal SO(5)/SO(4) coset with top partners in the four-plet and singlet of SO(4). In the down-type sector, some degree of alignment is required if all down-type quarks are elementary. We show that taking the bottom quark partially composite provides a dynamical explanation for the hierarchy causing this alignment. We present explicit realisations of this mechanism which do not require to include additional bottom partner fields. Finally, these conclusions are generalised to scenarios with non-minimal cosets and top partners in larger representations.