2,260 research outputs found
Fermion masses and mixing in models with SO(10) x A_4 symmetry
We study the flavour sector in models where the three families of matter are
unified in a representation of the group. The
necessary ingredients to realize tri-bi-maximal mixing in the lepton sector are
identified systematically. The non-renormalizable operators contributing to the
fermion mass matrices play an important role. We also present a mechanism to
explain the inter-family mass hierarchy of quarks and charged leptons, which
relies on a `universal seesaw' mechanism and is compatible with tri-bi-maximal
mixing.Comment: 24 pages, revte
Flavor and electroweak symmetry breaking at the TeV scale
We present a unified picture of flavor and electroweak symmetry breaking at
the TeV scale. Flavor and Higgs bosons arise as pseudo-Goldstone modes in a
nonlinear sigma model. Explicit collective symmetry breaking yields stable
vacuum expectation values and masses protected at one loop by the little-Higgs
mechanism. The coupling to the fermions through a Yukawa lagrangian with a U(1)
global flavor symmetry generates well-definite mass textures that correctly
reproduce the mass hierarchies and mixings of quarks and leptons. The model is
more constrained than usual little- Higgs models because of bounds on weak and
flavor physics. The main experimental signatures testable at the LHC are a
rather large mass mh0 = 317+/-80 GeV for the (lightest) Higgs boson and a
characteristic spectrum of new bosons and fermions with masses around the TeV
scale
Neutrino Mass Sum-rules in Flavor Symmetry Models
Four different neutrino mass sum-rules have been analyzed: these frequently
arise in flavor symmetry models based on the groups A_4, S_4 or T', which are
often constructed to generate tri-bimaximal mixing. In general, neutrino mass
can be probed in three different ways, using beta decay, neutrino-less double
beta decay and cosmology. The general relations between the corresponding three
neutrino mass observables are well known. The sum-rules lead to relations
between the observables that are different from the general case and therefore
only certain regions in parameter space are allowed. Plots of the neutrino mass
observables are given for the sum-rules, and analytical expressions for the
observables are provided. The case of deviations from the exact sum-rules is
also discussed, which can introduce new features. The sum-rules could be used
to distinguish some of the many models in the literature, which all lead to the
same neutrino oscillation results.Comment: 22 pages, 10 figures; matches the version published in Nuclear
Physics
Probing the Majorana nature of the neutrino with neutrinoless double beta decay
Neutrinoless double beta decay (NDBD) is the only experiment that could probe
the Majorana nature of the neutrino. Here we study the theoretical implications
of NDBD for models yielding tri-bimaximal lepton mixing like A4 and S4.Comment: Talk given at TAUP09, July 1-5, 2009 (Roma).The proceeding will be
published in Journal of Physics, Conference Series (Editors: E. Coccia, L.
Pandola, N. Fornengo, R. Aloisio
Teorema di fluttuazione-dissipazione per processi non poissoniani di rinnovo
Estendo il teorema di fluttuazione-dissipazione al caso non-stazionario di statistiche non-poissoniane che utilizzano la teoria del rinnov
Tri-bimaximal Neutrino Mixing from A(4) and \theta_{13} \sim \theta_C
It is a common believe that, if the Tri-bimaximal mixing (TBM) pattern is
explained by vacuum alignment in an A(4) model, only a very small reactor
angle, say \theta_{13} \sim \lambda^2_C being \lambda_C \equiv \theta_C the
Cabibbo angle, can be accommodated. This statement is based on the assumption
that all the flavon fields acquire VEVs at a very similar scale and the
departures from exact TBM arise at the same perturbation level. From the
experimental point of view, however, a relatively large value \theta_{13} \sim
\lambda_C is not yet excluded by present data. In this paper, we propose a
Seesaw A(4) model in which the previous assumption can naturally be evaded. The
aim is to describe a \theta_{13} \sim \lambda_C without conflicting with the
TBM prediction for \theta_{12} which is rather close to the observed value (at
\lambda^2_C level). In our model the deviation of the atmospherical angle from
maximal is subject to the sum-rule: \sin ^2 \theta_{23} \approx 1/2 +
\sqrt{2}/2 \sin \delta \cos \theta_{13} which is a next-to-leading order
prediction of our model.Comment: 16 pages, revised, typos corrected, references adde
Admixture of quasi-Dirac and Majorana neutrinos with tri-bimaximal mixing
We propose a realization of the so-called bimodal/schizophrenic model
proposed recently. We assume S4, the permutation group of four objects as
flavor symmetry giving tri-bimaximal lepton mixing at leading order. In these
models the second massive neutrino state is assumed quasi-Dirac and the
remaining neutrinos are Majorana states. In the case of inverse mass hierarchy,
the lower bound on the neutrinoless double beta decay parameter m_ee is about
two times that of the usual lower bound, within the range of sensitivity of the
next generation of experiments.Comment: 8 pages, minor changes to match version accepted in PL
- …