1,301 research outputs found
A Highly Predictive Ansatz for Leptonic Mixing and CP Violation
We suggest a simple highly predictive ansatz for charged lepton and light
neutrino mass matrices, based on the assumption of universality of Yukawa
couplings. Using as input the charged lepton masses and light neutrino masses,
the six parameters characterizing the leptonic mixing matrix , are
predicted in terms of a single phase , which takes a value around
. Correlations among variuos physical quantities are
obtained, in particular is predicted as a function of
, and , and
restricted to the range .Comment: 9 pages, 4 figure
Leptonic Invariants, Neutrino Mass-Ordering and the Octant of
We point out that leptonic weak-basis invariants are an important tool for
the study of the properties of lepton flavour models. In particular, we show
that appropriately chosen invariants can give a clear indication of whether a
particular lepton flavour model favours normal or inverted hierarchy for
neutrino masses and what is the octant of . These invariants can
be evaluated in any conveniently chosen weak-basis and can also be expressed in
terms of neutrino masses, charged lepton masses, mixing angles and CP violation
phases.Comment: 10 pages, no figure
Non-Factorizable Phases, Yukawa Textures and the Size of sin (2 beta)
We emphasize the crucial r\^ ole played by non-factorizable phases in the
analysis of the Yukawa flavour structure performed in weak bases with Hermitian
mass matrices and with vanishing entries. We show that non-factorizable
phases are important in order to generate a sufficiently large .
A method is suggested to reconstruct the flavour structure of Yukawa couplings
from input experimental data both in this Hermitian basis and in a
non-Hermitian basis with a maximal number of texture zeros. The corresponding
Froggatt--Nielsen patterns are presented in both cases.Comment: 15 pages, 3 figure
What if the Masses of the First Two Quark Families are not Generated by the Standard Higgs?
We point out that, in the context of the SM, is
expected to be large, of order one. The fact that motivates the introduction of a symmetry S which
leads to , with only the third generation of
quarks acquiring mass. We consider two scenarios for generating the mass of the
first two quark generations and full quark mixing. One consists of the
introduction of a second Higgs doublet which is neutral under S. The second
scenario consists of assuming New Physics at a high energy scale , contributing
to the masses of light quark generations, in an effective field theory
approach. This last scenario leads to couplings of the Higgs particle to
and which are significantly enhanced with
respect to those of the SM. In both schemes, one has scalar-mediated flavour-
changing neutral currents which are naturally suppressed. Flavour violating top
decays are predicted in the second scenario at the level \mbox{Br} (t
\rightarrow h c ) \geq 5\times 10^{-5}.Comment: 11 pages, 1 figur
Quasidegeneracy of Majorana Neutrinos and the Origin of Large Leptonic Mixing
We propose that the observed large leptonic mixing may just reflect a
quasidegeneracy of three Majorana neutrinos. The limit of exact degeneracy of
Majorana neutrinos is not trivial, as leptonic mixing and even CP violation may
occur. We conjecture that the smallness of , when compared to the
other elements of , may just reflect the fact that, in the limit of
exact mass degeneracy, the leptonic mixing matrix necessarily has a vanishing
element. We show that the lifting of the mass degeneracy can lead to the
measured value of while at the same time accommodating the observed
solar and atmospheric mixing angles. In the scenario we consider for the
breaking of the mass degeneracy there is only one CP violating phase, already
present in the limit of exact degeneracy, which upon the lifting of the
degeneracy generates both Majorana and Dirac-type CP violation in the leptonic
sector. We analyse some of the correlations among physical observables and
point out that in most of the cases considered, the implied strength of
leptonic Dirac-type CP violation is large enough to be detected in the next
round of experiments.Comment: 16 pages, 4 figures. Matches published version, references added,
improved discussion, results unchange
Yukawa Textures, New Physics and Nondecoupling
We point out that New Physics can play an important r\^ ole in rescuing some
of the Yukawa texture zero ans\" atze which would otherwise be eliminated by
the recent, more precise measurements of . As an example, a detailed
analysis of a four texture zero ansatz is presented, showing how the presence
of an isosinglet vector-like quark which mixes with standard quarks, can render
viable this Yukawa texture. The crucial point is the nondecoupling of the
effects of the isosinglet quark, even for arbitrary large values of its mass.Comment: 13 pages, no figure
Vector-like Quarks at the Origin of Light Quark Masses and Mixing
We show how a novel fine-tuning problem present in the Standard Model can be
solved through the introduction of a single flavour symmetry G, together with
three quarks, three quarks, as well as a complex singlet
scalar. The symmetry G is extended to the additional fields and it is an exact
symmetry of the Lagrangian, only spontaneously broken by the vacuum. Specific
examples are given and a phenomenological analysis of the main features of the
model is presented. It is shown that even for vector-like quarks with masses
accessible at the LHC, one can have realistic quark masses and mixing, while
respecting the strict constraints on process arising from flavour changing
neutral currents (FCNC). The vector-like quark decay channels are also
described.Comment: 25 pages, no figure
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