We consider seesaw type-I models including at least one (mostly-)sterile neutrino with mass at the eV scale. Three distinct situations are found, where the presence of light extra neutrinos is naturally justified by an approximately conserved lepton number symmetry. To analyse these scenarios consistently, it is crucial to employ an exact parametrisation of the full mixing matrix...
Abstract We explore some aspects of models with two and three SU(2) scalar doublets that lead to mass degeneracies among some of the physical scalars. In Higgs sectors with two scalar doublets, the exact degeneracy of scalar masses, without an artificial fine-tuning of the scalar potential parameters, is possible only in the case of the inert doublet model (IDM), where the scalar...
We point out that leptonic weak-basis invariants are an important tool for the study of the properties of lepton flavour models. In particular, we show that appropriately chosen invariants can give a clear indication of whether a particular lepton flavour model favours normal or inverted hierarchy for neutrino masses and what is the octant of θ 23. These invariants can be...
We show how a novel fine-tuning problem present in the Standard Model can be solved through the introduction of a \(Z_6\) flavour symmetry, together with three \(Q = - 1/3\) quarks, three \(Q = 2/3\) quarks, as well as a complex singlet scalar. The \(Z_6\) symmetry is extended to the additional fields and it is an exact symmetry of the Lagrangian, only softly broken in the scalar...
We analyse various flavour-changing processes like \(t\rightarrow hu,hc\), \(h\rightarrow \tau e,\tau \mu \) as well as hadronic decays \(h\rightarrow bs,bd\), in the framework of a class of two Higgs doublet models where there are flavour-changing neutral scalar currents at tree level. These models have the remarkable feature of having these flavour-violating couplings entirely...
Abstract We present a detailed study of the vacua of the S 3-symmetric three-Higgs-doublet potential, specifying the region of parameters where these minimisation solutions occur. We work with a CP conserving scalar potential and analyse the possible real and complex vacua with emphasis on the cases in which the CP symmetry can be spontaneously broken. Results are presented both...
In the context of two Higgs doublet models, we study the conditions required in order to have stable quasi-alignment in flavour space. We show that stability under the renormalisation group equations imposes strong constraints on the flavour structure of the Yukawa couplings associated to each one of the Higgs doublets. In particular, we find a novel solution, where all Yukawa...
AbstractWe analyse the constraints and some of the phenomenological implications of a class of two Higgs doublet models where there are flavour-changing neutral currents (FCNC) at tree level but the potentially dangerous FCNC couplings are suppressed by small entries of the CKM matrix V. This class of models have the remarkable feature that, as a result of a discrete symmetry of...
We study the transition from perturbative QCD to Chiral Dynamics (linear σ model), which describe physics between MW, and µ, and between µ and Mπ, respectively. This is done within the context of K decays. The smoothness of the transition is shown by comparing the explicit form of the anomalous dimension matrices in both pictures and checking the approximate cancellation of the...
This chapter of the report of the “Flavor in the era of the LHC” Workshop discusses the theoretical, phenomenological and experimental issues related to flavor phenomena in the charged lepton sector and in flavor conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavor structure of fundamental particles. We...
