Cherif Hamzaoui

Unified flavor symmetry from warped dimensions

a b s t r a c t In a model of warped extra-dimensions with all matter fields in the bulk, we propose a scenario which explains all the masses and mixings of the SM fermions. In this scenario, the same flavor symmetric structure is imposed on all the fermions of the Standard Model (SM), including neutrinos. Due to the exponential sensitivity on bulk fermion masses, a small breaking of this symmetry can be greatly enhanced and produce seemingly un-symmetric hierarchical masses and small mixing angles among the charged fermion zero-modes (SM quarks and charged leptons), thus washing out visible effects of the symmetry. If the Dirac neutrinos are sufficiently localized towards the UV boundary, and the Higgs field leaking into the bulk, the neutrino mass hierarchy and flavor structure will still be largely dominated and reflect the fundamental flavor structure, whereas localization of the quark sector would reflect the effects of the flavor symmetry breaking sector. We explore these features in an example based on which a family permutation symmetry is imposed in both quark and lepton sectors.

Patterns in the fermion mixing matrix, a bottom-up approach

We first obtain the most general and compact parametrization of the unitary transformation diagonalizing any 3×3 Hermitian matrix H, as a function of its elements and eigenvalues. We then study a special class of fermion mass matrices, defined by the requirement that all of the diagonalizing unitary matrices (in the up, down, charged lepton, and neutrino sectors) contain at least one mixing angle much smaller than the other two. Our new parametrization allows us to quickly extract information on the patterns and predictions emerging from this scheme. In particular we find that the phase difference between two elements of the two mass matrices (of the sector in question) controls the generic size of one of the observable fermion mixing angles: i.e. just fixing that particular phase difference will predict the generic value of one of the mixing angles, irrespective of the value of anything else.

A simplified approach to determine α and the penguin amplitude in Bd → ππ

Abstract The effect of inelastic final-state interactions (IFSIs) on the determination of the weak phase α from the isospin triangles of B → ππ is qualitatively illustrated. Neglecting the electroweak penguins and IFSIs and assuming the dominance of the top-quark loop in strong penguin diagrams, we propose an experimentally accessible way to approximately determine α and the penguin amplitude in B d → ππ . This approach relies on a simplified isospin consideration and the factorization approximation, and its feasibility is irrelevant to the time-dependent measurements of B d → ππ .

Up-down unification just above the supersymmetric threshold

Abstract. Large corrections to the quark mass matrices at the supersymmetric threshold allow the theory to have identical Yukawa matrices in the superpotential. We demonstrate that up–down unification can take place in a moderate quark–squark alignment scenario with an average squark mass of the order 1 TeV and with

Fermion Masses and Mixing in General Warped Extra Dimensional Models

\tan\beta>15

Partial

.

\mu-\tau

We analyze fermion masses and mixing in a general warped extra dimensional model, where all the Standard Model (SM) fields, including the Higgs, are allowed to propagate in the bulk. In this context, a slightly broken flavor symmetry imposed universally on all fermion fields, without distinction, can generate the full flavor structure of the SM, including quarks, charged leptons and neutrinos. For quarks and charged leptons, the exponential sensitivity of their wave-functions to small flavor breaking effects yield naturally hierarchical masses and mixing as it is usual in warped models with fermions in the bulk. In the neutrino sector, the exponential wave-function factors can be flavor-blind and thus insensitive to the small flavor symmetry breaking effects, directly linking their masses and mixing angles to the flavor symmetric structure of the 5D neutrino Yukawa couplings. The Higgs must be localized in the bulk and the model is naturally more successful in generalized warped scenarios where the metric background solution is different than AdS5. We study these features in two simple frameworks, flavor complimentarily, and flavor democracy, which provide specific predictions and correlations between quarks and leptons, testable as more precise data in the neutrino sector becomes available.

textures and leptogenesis

Motivated by the recent results from Daya Bay, Reno and Double Chooz Collaborations, we study the consequences of small departures from exact μ − τ symmetry in the neutrino sector, to accommodate a nonvanishing value of the element Ve3 from the leptonic mixing matrix. Within the seesaw framework, we identify simple patterns of Dirac mass matrices that lead to approximate μ − τ symmetric neutrino mass matrices, which are consistent with the neutrino oscillation data and lead to nonvanishing mixing angle Ve3 as well as precise predictions for the CP-violating phases. We also show that there is a transparent link between neutrino mixing angles and seesaw parameters, which we further explore within the context of leptogenesis as well as double beta decay phenomenology.

Canonical constraints on leptonic CP violation using ultrahigh energy cosmic ray neutrino fluxes

It is shown that one can in principle constrain the CP-violating parameter δ from measurements of four independent |Vij|2’s, or three |Vij|2’s and a ratio of two of them, in the leptonic sector. To quantify our approach, using unitarity, we derive simple expressions in terms of four independent |Vij|2’s for cosδ, and an expression for sin2δ from J2. Thus, depending on the values for |Vij| and their accuracy, we can set meaningful limits on |δ|. To illustrate numerically, if |Vμ1|2 is close to 0.1 with a 10% precision, and if |Ve3|2 is larger than 0.005 and for values of |Ve2|2 and |Vμ3|2 that stay within ±0.1 of the current experimental data leads to a bound: π/2≤|δ|≤π. Alternatively, a certain combination of parameters with values of |Ve3|2 larger than 0.01 leads to a closed bound of 73≤|δ|≤103. In general, we find that it is better to use |Vμ1|2 or |Vτ1|2 as the fourth independent |Vij|2 and that, over most of the parameter space, δ is least sensitive to |Ve3|2. With just three independent measurements (solar, atmospheric, and reactor), it is impossible to set limits on the CP phase. In this respect, we study the use of ultrahigh energy cosmic ray neutrino fluxes as the additional fourth information. We find that within the SM, neutrino fluxes of all three flavors will be very similar but that pushing current neutrino data to their extreme values still allowed, ratios of cosmic neutrino fluxes can differ by up to 20%; such large discrepancies could imply negligibly small CP violation. We also study a nonradiative neutrino decay model and find that the neutrino fluxes can differ by a factor of up to 3 within this model and that an accuracy of 10% on the neutrino fluxes is sufficient to set interesting limits on δ.

How natural is a small anti-Theta in left-right SUSY models?

In a world without an axion, the smallness of θ-bar may be achieved due to a spontaneously broken discrete left-right symmetry. We analyze the radiatively induced θ-bar in the context of generic left-right symmetric supersymmetry models without assuming flavor degeneracy in the squark sector. Left-right symmetry allows us to keep θ-bar within its present bound only if the intergenerational mass splitting in the squark sector at the scale of the left-right symmetry breaking is smaller than 0.5%. We also consider the naturalness of the mu=0 solution to the strong CP problem in the context of horizontal flavor symmetries. A strong bound on the combination of the horizontal charges in the up quark sector is found in this case