17 research outputs found
Majorana Neutrinos, Neutrino Mass Spectrum and the |<m>| ~ 0.001 eV Frontier in Neutrinoless Double Beta Decay
If future neutrino oscillation experiments show that the neutrino mass
spectrum is with normal ordering, m1 < m2 < m3, and the searches for
neutrinoless double beta-decay with sensitivity to values of the effective
Majorana mass || > 0.01 eV give negative results, the next frontier in the
quest for neutrinoless double beta-decay will correspond to || ~ 0.001 eV.
Assuming that massive neutrinos are Majorana particles and their exchange is
the dominant mechanism generating neutrinoless double beta-decay, we analise
the conditions under which ||, in the case of three neutrino mixing and
neutrino mass spectrum with normal ordering, would satisfy || > 0.001 eV. We
consider the specific cases of i) normal hierarchical neutrino mass spectrum,
ii) of relatively small value of the CHOOZ angle theta13 as well as iii) the
general case of spectrum with normal ordering, partial hierarchy and a value of
theta13 close to the existing upper limit. We study the ranges of the lightest
neutrino mass m1 and/or of sin^2 theta13, for which ||> 0.001 eV and discuss
the phenomenological implications of such scenarios. We provide also an
estimate of || when the three neutrino masses and the neutrino mixing
originate from neutrino mass term of Majorana type for the (left-handed)
flavour neutrinos and m1 Ue1^2 + m2 U_e2^2 + m3 Ue3^2 =0, but there does not
exist a symmetry which forbids the neutrinoless double beta-decay.Comment: 29 pages, 6 eps figure
The Interplay Between the "Low" and "High" Energy CP-Violation in Leptogenesis
We analyse within the "flavoured" leptogenesis scenario of baryon asymmetry
generation, the interplay of the "low energy" CP-violation, originating from
the PMNS neutrino mixing matrix , and the "high energy" CP-violation which
can be present in the matrix of neutrino Yukawa couplings, , and can
manifest itself only in "high" energy scale processes. The type I see-saw model
with three heavy right-handed Majorana neutrinos having hierarchical spectrum
is considered. The "orthogonal" parametrisation of the matrix of neutrino
Yukawa couplings, which involves a complex orthogonal matrix , is employed.
In this approach the matrix is the source of "high energy" CP-violation.
Results for normal hierarchical (NH) and inverted hierarchical (IH) light
neutrino mass spectrum are derived in the case of decoupling of the heaviest RH
Majorana neutrino. It is shown that taking into account the contribution to
due to the CP-violating phases in the neutrino mixing matrix can
change drastically the predictions for , obtained assuming only "high
energy" CP-violation from the -matrix is operative in leptogenesis. In the
case of IH spectrum, in particular, there exist significant regions in the
corresponding parameter space where the purely "high energy" contribution in
plays a subdominant role in the production of baryon asymmetry compatible
with the observations.Comment: Results unchanged; comments and references added; version to be
puplished in Eur.Phys.J.
The mu - e Conversion in Nuclei, mu --> e gamma, mu --> 3e Decays and TeV Scale See-Saw Scenarios of Neutrino Mass Generation
We perform a detailed analysis of lepton flavour violation (LFV) within
minimal see-saw type extensions of the Standard Model (SM), which give a viable
mechanism of neutrino mass generation and provide new particle content at the
electroweak scale. We focus, mainly, on predictions and constraints set on each
scenario from mu --> e gamma, mu --> 3e and mu - e conversion in the nuclei. In
this class of models, the flavour structure of the Yukawa couplings between the
additional scalar and fermion representations and the SM leptons is highly
constrained by neutrino oscillation measurements. In particular, we show that
in some regions of the parameters space of type I and type II see-saw models,
the Dirac and Majorana phases of the neutrino mixing matrix, the ordering and
hierarchy of the active neutrino mass spectrum as well as the value of the
reactor mixing angle theta_{13} may considerably affect the size of the LFV
observables. The interplay of the latter clearly allows to discriminate among
the different low energy see-saw possibilities.Comment: Expressions for the factors |C_{me}|^2 and |C_{mu3e}|^2 in the mu-e
conversion and mu-->3e decay rates, eqs. (36) and (49), respectively,
corrected; results in subsections 2.2 and 2.3 quantitatively changed,
qualitatively remain the same; figures 2, 3, 4 and 5 replace
The Absolute Neutrino Mass Scale, Neutrino Mass Spectrum, Majorana CP-Violation and Neutrinoless Double-Beta Decay
Assuming 3- mixing, massive Majorana neutrinos and neutrinoless
double-beta (\betabeta-) decay generated only by the (V-A) charged current weak
interaction via the exchange of the three Majorana neutrinos, we briefly review
the predictions for the effective Majorana mass \meff in \betabeta-decay and
reanalyse the physics potential of future \betabeta-decay experiments to
provide information on the type of neutrino mass spectrum, the absolute scale
of neutrino masses, and Majorana CP-violation in the lepton sector. Using as
input the most recent experimental results on neutrino oscillation parameters
and the prospective precision that can be achieved in future measurements of
the latter, we perform a statistical analysis of a \betabeta-decay half-life
measurement taking into account experimental and theoretical errors, as well as
the uncertainty implied by the imprecise knowledge of the corresponding nuclear
matrix element (NME). We show, in particular, how the possibility to
discriminate between the different types of neutrino mass spectra and the
constraints on the absolute neutrino mass scale depend on the mean value and
the experimental error of \meff and on the NME uncertainty. The constraints
on Majorana CP-violation phases in the neutrino mixing matrix, which can be
obtained from a measurement of \meff and additional data on the sum of
neutrino masses, are also investigated in detail. We estimate the required
experimental accuracies on both types of measurements, and the required
precision in the NME permitting to address the issue of Majorana CP-violation
in the lepton sector.Comment: 29 pages, 7 figures, minor improvements on the text, fig. 4 improved
graphically, version to appear in Nucl. Phys.
Supersymmetric mass spectra and the seesaw type-I scale
We calculate supersymmetric mass spectra with cMSSM boundary conditions and a
type-I seesaw mechanism added to explain current neutrino data. Using
published, estimated errors on SUSY mass observables for a combined LHC+ILC
analysis, we perform a theoretical analysis to identify parameter
regions where pure cMSSM and cMSSM plus seesaw type-I might be distinguishable
with LHC+ILC data. The most important observables are determined to be the
(left) smuon and selectron masses and the splitting between them, respectively.
Splitting in the (left) smuon and selectrons is tiny in most of cMSSM parameter
space, but can be quite sizeable for large values of the seesaw scale,
. Thus, for very roughly GeV hints for type-I
seesaw might appear in SUSY mass measurements. Since our numerical results
depend sensitively on forecasted error bars, we discuss in some detail the
accuracies, which need to be achieved, before a realistic analysis searching
for signs of type-I seesaw in SUSY spectra can be carried out.Comment: 17 pages, 7 figure
Majorana Neutrino Mixing
The most plausible see-saw explanation of the smallness of the neutrino
masses is based on the assumption that total lepton number is violated at a
large scale and neutrinos with definite masses are Majorana particles. In this
review we consider in details difference between Dirac and Majorana neutrino
mixing and possibilities of revealing Majorana nature of neutrinos with
definite masses
Charged Lepton Flavour Violating Radiative Decays in See-Saw Models with Symmetry
The charged lepton flavour violating (LFV) radiative decays, , and are investigated in a
class of supersymmetric models with three heavy right-handed (RH)
Majorana neutrinos, in which the lepton (neutrino) mixing is predicted to
leading order (LO) to be tri-bimaximal. The light neutrino masses are generated
via the type I see-saw mechanism. The analysis is done within the framework of
the minimal supergravity (mSUGRA) scenario, which provides flavour universal
boundary conditions at the scale of grand unification GeV. Detailed predictions for the rates of the three LFV decays are
obtained in two explicit realisations of the models due to Altarelli and
Feruglio and Altarelli and Meloni, respectively.Comment: Results unchanged, minor improvements made; version accepted for
publication in JHE
Models of Neutrino Masses and Mixings
We review theoretical ideas, problems and implications of neutrino masses and
mixing angles. We give a general discussion of schemes with three light
neutrinos. Several specific examples are analyzed in some detail, particularly
those that can be embedded into grand unified theories.Comment: 44 pages, 2 figures, version accepted for publication on the Focus
Issue on 'Neutrino Physics' edited by F.Halzen, M.Lindner and A. Suzuki, to
be published in New Journal of Physics
A combined beta-beam and electron capture neutrino experiment
The next generation of long baseline neutrino experiments will aim at
determining the value of the unknown mixing angle, theta_{13}, the type of
neutrino mass hierarchy and the presence of CP-violation in the lepton sector.
Beta-beams and electron capture experiments have been studied as viable
candidates for long baseline experiments. They use a very clean electron
neutrino beam from the beta-decays or electron capture decays of boosted ions.
In the present article we consider an hybrid setup which combines a beta-beam
with an electron capture beam by using boosted Ytterbium ions. We study the
sensitivity to the CP-violating phase delta and the theta_{13} angle, the
CP-discovery potential and the reach to determine the type of neutrino mass
hierarchy for this type of long baseline experiment. The analysis is performed
for different neutrino beam energies and baselines. Finally, we also discuss
how the results would change if a better knowledge of some of the assumed
parameters was achieved by the time this experiment could take place.Comment: 35 pp, 11 fig