Asmaa Abada

Flavour issues in leptogenesis

We study the impact of flavour in thermal leptogenesis, including the quantum oscillations of the asymmetries in lepton flavour space. In the Boltzmann equations we find different numerical factors and additional terms which can affect the results significantly. The upper bound on the CP asymmetry in a specific flavour is weaker than the bound on the sum. This suggests that -- when flavour dynamics is included -- there is no model-independent limit on the light neutrino mass scale,and that the lower bound on the reheat temperature is relaxed by a factor ~ (3 - 10).

Flavour matters in leptogenesis

We give analytic approximations to the baryon asymmetry produced by thermal leptogenesis with hierarchical right-handed neutrinos. Our calculation includes flavour-dependent washout processes and CP violation in scattering, and neglects gauge interactions and finite temperature corrections. Our approximate formulae depend upon the three CP asymmetries in the individual lepton flavours as well as on three flavour-dependent efficiency factors. We show that the commonly used expressions for the lepton asymmetry, which depend on the total CP asymmetry and one single efficiency factor, may fail to reproduce the correct lepton asymmetry in a number of cases. We illustrate the importance of using the flavour-dependent formulae in the context of a two right-handed neutrino model.

Low energy effects of neutrino masses

While all models of Majorana neutrino masses lead to the same dimension five effective operator, which does not conserve lepton number, the dimension six operators induced at low energies conserve lepton number and differ depending on the high energy model of new physics. We derive the low-energy dimension six operators which are characteristic of generic Seesaw models, in which neutrino masses result from the exchange of heavy fields which may be either fermionic singlets, fermionic triplets or scalar triplets. The resulting operators may lead to effects observable in the near future, if the coefficients of the dimension five and six operators are decoupled along a certain pattern, which turns out to be common to all models. The phenomenological consequences are explored as well, including their contributions to μ→eγ and new bounds on the Yukawa couplings for each model.

Heavy → light semileptonic decays of pseudoscalar mesons from lattice QCD

Abstract We have computed the form factors for B → π and D → K ( π ) semileptonic decays on the lattice by using full non-perturbative O (a) improvement, in the quenched approximation. Our results are expressed in terms of few parameters which describe the q 2 -dependence and normalization of the form factors.We have computed the form factors for B -->pi and D -->K(pi) semileptonic decays on the lattice by using full non-perturbative O(a) improvement, in the quenched approximation. Our results are expressed in terms of few parameters which describe the q^2-dependence and normalization of the form factors.

μ→Eγ and τ→lγ decays in the fermion triplet seesaw model

In the framework of the seesaw models with triplets of fermions, we evaluate the decay rates of

Meson spectroscopy and decay constants with Wilson fermions at β = 6.4

\mu \to e \gamma

Tree-level lepton universality violation in the presence of sterile neutrinos: impact for

and

R_K

\tau \to l \gamma

and

transitions. We show that although, due to neutrino mass constraints, those rates are in general expected to be well under the present experimental limits, this is not necessarily always the case. Interestingly enough, the observation of one of those decays in planned experiments would nevertheless contradict bounds stemming from present experimental limits on the

R_\pi

\mu \to eee