David Emmanuel-Costa

Geometrical spontaneous C P violation

Spontaneous CP-violating phases that do not depend on the parameters of the Higgs sector - the so-called calculable phases - are investigated. The simplest realization is in models with 3 Higgs doublets, in which the scalar potential is invariant under non-Abelian symmetries. The non-Abelian discrete group Delta(54) is shown to lead to the known structure of calculable phases obtained with Delta(27). We investigate the possibily of accommodating the observed fermion masses and mixings.

Geometrical CP violation from non-renormalisable scalar potentials

Abstract We consider in detail the non-renormalisable scalar potential of three Higgs doublets transforming as an irreducible triplet of Δ ( 27 ) or Δ ( 54 ) . We start from a renormalisable potential that spontaneously leads to a vacuum with CP-violating phases independent of arbitrary parameters – geometrical CP violation. Then we analyse to arbitrarily high order non-renormalisable terms that are consistent with the symmetry and we demonstrate that inclusion of non-renormalisable terms in the potential can preserve the geometrical CP-violating vacuum.

Texture zeros and weak basis transformations

Abstract We investigate the physical meaning of some of the “texture zeros” which appear in most of the Ansatze on quark masses and mixings. It is shown that starting from arbitrary quark mass matrices and making a suitable weak basis transformation one can obtain some of these sets of zeros which therefore have no physical content. We then analyse the physical implications of a four-texture zero Ansatz which is in agreement with all present experimental data.

Four Zero Neutrino Yukawa Textures in the Minimal Seesaw Framework

We investigate, within the type I seesaw framework, the physical implications of zero textures in the Yukawa couplings which generate the neutrino Dirac mass matrix

Weak Basis Transformations and Texture Zeros in the Leptonic Sector

{m}_{D}

Nearest-Neighbour Interaction from an Abelian Symmetry and Deviations from Hermiticity

. It is shown that four is the maximal number of texture zeros compatible with the observed leptonic mixing and the assumption that no neutrino mass vanishes. We classify all allowed four-zero textures of

New approach to the Yukawa puzzle

{m}_{D}

Flavour structure and proton decay in 6D orbifold GUTs

into two categories with three classes each. We show that the different classes, in general, admit

Minimal string-scale unification of gauge couplings

CP

Yukawa structure with maximal predictability

violation both at low and high energies. We further present the constraints obtained for low energy physics in each case. The role of these zero textures in establishing a connection between leptogenesis and low energy data is analyzed in detail. It is shown that it is possible in all cases to completely specify the parameters relevant for leptogenesis in terms of light neutrino masses and leptonic mixing together with the unknown heavy neutrino masses.