2,696 research outputs found
Hierarchical Matrices in the See-Saw Mechanism, large Neutrino Mixing and Leptogenesis
We consider the see-saw mechanism for hierarchical Dirac and Majorana
neutrino mass matrices m_D and M_R, including the CP violating phases. Simple
arguments about the structure of the neutrino mass matrix and the requirement
of successful leptogenesis lead to the situation that one of the right-handed
Majorana neutrinos is much heavier than the other two, which in turn display a
rather mild hierarchy. It is investigated how for the neutrino mixing one small
and two large angles are generated. The mixing matrix element |U_{e3}|^2 is
larger than 10^{-3} and a characteristic ratio between the branching ratios of
lepton flavor violating charged lepton decays \ell_j -> \ell_i \gamma is found.
Successful leptogenesis implies sizable CP violation in oscillation
experiments. As in the original minimal see-saw model, the signs of the baryon
asymmetry of the universe and of the CP asymmetry in neutrino oscillations are
equal and there is no connection between the leptogenesis phase and the
effective mass as measurable in neutrinoless double beta decay.Comment: 16 + 3 pages, 2 figures. To appear in Eur.Phys.J.
Relating the scalar flavour-changing neutral couplings to the CKM matrix
We build a class of two-Higgs-doublet models in which the flavour-changing
couplings of the neutral scalars are related in an exact way to elements of the
quark mixing matrix. In this framework, we explore the different possibilities
for CP violation and find some interesting scenarios, like a realization of the
superweak idea without CP violation in the -meson system. In another
scenario the neutral scalars can be relatively light, and their contributions
to the -- transitions can alter the standard-model predictions
for CP violation in that system.Comment: 12 pages LATEX, no figure
A three-parameter model for the neutrino mass matrix
Using the type-II seesaw mechanism with three Higgs doublets phi_alpha (alpha
= e, mu, tau) and four Higgs triplets, we build a model for lepton mixing based
on a 384-element horizontal symmetry group, generated by the permutation group
S_3 and by six Z_2 transformations. The charged-lepton mass matrix is diagonal;
the symmetries of the model would require all the three masses m_alpha to be
equal, but different vacuum expectation values of the phi_alpha allow the
m_alpha to split. The number of parameters in the Majorana neutrino mass matrix
m_nu depends on two options: full breaking of the permutation group S_3, or
leaving a mu--tau interchange symmetry intact; and hard or spontaneous
violation of CP. We discuss in detail the case with the minimal number of three
parameters, wherein m_nu is real, symmetric under mu--tau interchange, and has
equal diagonal elements. In that case, CP is conserved in lepton mixing,
atmospheric neutrino mixing is maximal, and theta_{13} = 0; moreover, the type
of neutrino mass spectrum and the absolute neutrino mass scale are sensitive
functions of the solar mixing angle.Comment: 16 pages, one eps figure; some clarifications added, contains new
section 5, version accepted for publication in J. Phys.
Torque Ripple Minimization in a Switched Reluctance Drive by Neuro-Fuzzy Compensation
Simple power electronic drive circuit and fault tolerance of converter are
specific advantages of SRM drives, but excessive torque ripple has limited its
use to special applications. It is well known that controlling the current
shape adequately can minimize the torque ripple. This paper presents a new
method for shaping the motor currents to minimize the torque ripple, using a
neuro-fuzzy compensator. In the proposed method, a compensating signal is added
to the output of a PI controller, in a current-regulated speed control loop.
Numerical results are presented in this paper, with an analysis of the effects
of changing the form of the membership function of the neuro-fuzzy compensator.Comment: To be published in IEEE Trans. on Magnetics, 200
Tree FCNC and non-unitarity of CKM matrix
We discuss possible signatures of the tree level FCNC, which results from the
non-unitarity of CKM matrix. We first define the unitaity step-by-step, and
possible test of the non-unitaity through the 4-value-KM parametrization. We,
then, show how the phase angle of the unitary triangle would change in case of
the vector-like down quark model. As another example of tree FCNC, we
investigate the leptophobic model and its application to the recent
mixing measurements.Comment: Talk given at Neutrino Masses and Mixings 2006 (NMM2006), Shizuoka,
Japan (December 2006
Mean-field calculation of critical parameters and log-periodic characterization of an aperiodic-modulated model
We employ a mean-field approximation to study the Ising model with aperiodic
modulation of its interactions in one spatial direction. Two different values
for the exchange constant, and , are present, according to the
Fibonacci sequence. We calculated the pseudo-critical temperatures for finite
systems and extrapolate them to the thermodynamic limit. We explicitly obtain
the exponents , , and and, from the usual scaling
relations for anisotropic models at the upper critical dimension (assumed to be
4 for the model we treat), we calculate , , , ,
and . Within the framework of a renormalization-group approach, the
Fibonacci sequence is a marginal one and we obtain exponents which depend on
the ratio , as expected. But the scaling relation is obeyed for all values of we studied. We characterize
some thermodynamic functions as log-periodic functions of their arguments, as
expected for aperiodic-modulated models, and obtain precise values for the
exponents from this characterization.Comment: 17 pages, including 9 figures, to appear in Phys. Rev.
Geometrical CP violation in multi-Higgs models
We introduce several methods to obtain calculable phases with geometrical
values that are independent of arbitrary parameters in the scalar potential.
These phases depend on the number of scalars and on the order of the discrete
non-Abelian group considered. Using these methods we present new geometrical CP
violation candidates with vacuum expectation values that must violate CP (the
transformation that would make them CP conserving is not a symmetry of the
potential). We also extend to non-renormalisable potentials the proof that more
than two scalars are needed to obtain these geometrical CP violation
candidates.Comment: 8 pages, 2 figures. v2: table added, accepted by JHE
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