7,460 research outputs found
Tripartite Neutrino Mass Matrix
The 3 X 3 Majorana neutrino mass matrix is written as a sum of 3 terms, i.e.
M_nu = M_A + M_B + M_C, where M_A is proportional to the identity matrix and
M_B and M_C are invariant under different Z_3 transformations. This M_nu is
very suitable for understanding atmospheric and solar neutrino oscillations,
with sin^2 (2 theta_atm) and tan^2 (theta_sol) fixed at 1 and 0.5 respectively,
in excellent agreement with present data. It has in fact been proposed before,
but only as an ansatz. This paper uncovers its underlying symmetry, thus
allowing a complete theory of leptons and quarks to be constructed.Comment: 9 pages, no figur
Dirac Neutrinos and Dark Matter Stability from Lepton Quarticity
We propose to relate dark matter stability to the possible Dirac nature of
neutrinos. The idea is illustrated in a simple scheme where small Dirac
neutrino masses arise from a type--I seesaw mechanism as a result of a
discrete lepton number symmetry. The latter implies the existence of a viable
WIMP dark matter candidate, whose stability arises from the same symmetry which
ensures the Diracness of neutrinos.Comment: 12 pages, 6 figures, Report N IFIC/16-4
Minimal supergravity radiative effects on the tri-bimaximal neutrino mixing pattern
We study the stability of the Harrison-Perkins-Scott (HPS) mixing pattern,
assumed to hold at some high energy scale, against supersymmetric radiative
corrections. We work in the framework of a reference minimal supergravity model
(mSUGRA) where supersymmetry breaking is universal and flavor-blind at
unification. The radiative corrections considered include both RGE running as
well as threshold effects. We find that in this case the solar mixing angle can
only increase with respect to the HPS reference value, while the atmospheric
and reactor mixing angles remain essentially stable. Deviations from the solar
angle HPS prediction towards lower values would signal novel contributions from
physics beyond the simplest mSUGRA model.Comment: 13 pages, 3 figures; added reference; final version for publicatio
Predicting Neutrinoless Double Beta Decay
We give predictions for the neutrinoless double beta decay rate in a simple
variant of the A_4 family symmetry model. We show that there is a lower bound
for the neutrinoless double beta decay amplitude even in the case of normal
hierarchical neutrino masses, corresponding to an effective mass parameter
|m_{ee}| >= 0.17 \sqrt{\Delta m^2_{ATM}}. This result holds both for the CP
conserving and CP violating cases. In the latter case we show explicitly that
the lower bound on |m_{ee}| is sensitive to the value of the Majorana phase. We
conclude therefore that in our scheme, neutrinoless double beta decay may be
accessible to the next generation of high sensitivity experiments.Comment: 4 pages, 5 figures, 1 tabl
The local stellar population of nova regions in the Large Magellanic Cloud
This study aims at identifying and understanding the parent population of
novae in the Large Magellanic Cloud (LMC) by studying the local, projected,
stellar population. The star formation history of the local environment around
novae is studied based on photometric data of stars and star clusters in the
nova neighbourhood, available in the OGLE II survey and star cluster
catalogues. The ages of stellar population within a few arcmin around novae
regions are estimated using isochrone fits to the V vs (V-I) colour-magnitude
diagrams. The fraction of stars in various evolutionary states are compared
using luminosity functions of the main-sequence stars and the red giant stars.
The age, density and luminosity function of the stellar population are
estimated around 15 novae. The upper limit of the age of the intermediate
stellar population is found to be 4 Gyr in all the regions, excepting the
region around the slow nova LMC 1948. Star formation in these regions is found
to have started between 4 - 2.0 Gyr, with a majority of the regions starting
the star formation at 3.2 Gyr. This star formation event lasted until 1.6 - 0.8
Gyr The star formation history of the underlying population of both the fast
and moderately fast novae indicate their parent population to be similar and
likely to be in the age range 3.2 - 1.0 Gyr. This is in good agreement with the
theoretical age estimates for Galactic cataclysmic variables. The region around
the slow nova shows a stellar population in the age range 1 - 10 Gyr, with a
good fraction belonging to an older population, consistent with the idea that
the progenitors of slow novae belong to older population.Comment: to appear in A&A (final version - error analysis included, typos
corrected, figures 17 and 18 changed
Underlying A(4) symmetry for the neutrino mass matrix and the quark mixing matrix
The discrete non-Abelian symmetry A4, valid at some high-energy scale, naturally leads to degenerate neutrino masses, without spoiling the hierarchy of charged-lepton masses. Realistic neutrino mass splittings and mixing angles (one of which is necessarily maximal and the other large) are then induced radiatively in the context of softly broken supersymmetry. The quark mixing matrix is also calculable in a similar way. The mixing parameter Ue3 is predicted to be imaginary, leading to maximal CP violation in neutrino oscillations. Neutrinoless double beta decay and τ→μγ should be in the experimentally accessible range
R--Parity Violating Signals for Chargino Production at LEP II
We study chargino pair production at LEP II in supersymmetric models with
spontaneously broken R-parity. We perform signal and background analyses,
showing that a large region of the parameter space of these models can be
probed through chargino searches at LEP II. In particular, we determine the
attainable limits on the chargino mass as a function of the magnitude of the
effective bilinear R-parity violation parameter , demonstrating that
LEP II is able to unravel the existence of charginos with masses almost up to
its kinematical limit even in the case of R-parity violation. This requires the
study of several final state topologies since the usual MSSM chargino signature
is recovered as . Moreover, for sufficiently large
values, for which the chargino decay mode dominates,
we find through a dedicated Monte Carlo analysis that the mass
bounds are again very close to the kinematic limit. Our results establish the
robustness of the chargino mass limit, in the sense that it is basically
model-independent. They also show that LEP II can establish the existence of
spontaneous R-parity violation in a large region of parameter space should
charginos be produced.Comment: improved analyses; 31 pages and 9 figures (included
Non-Abelian Discrete Symmetries and Neutrino Masses: Two Examples
Two recent examples of non-Abelian discrete symmetries (S_3 and A_4) in
understanding neutrino masses and mixing are discussed.Comment: 16 pages, no figure, invited contribution to NJP focus issue on
neutrino
A4-based tri-bimaximal mixing within inverse and linear seesaw schemes
We consider tri-bimaximal lepton mixing within low-scale seesaw schemes where
light neutrino masses arise from TeV scale physics, potentially accessible at
the Large Hadron Collider (LHC). Two examples are considered, based on the A4
flavor symmetry realized within the inverse or the linear seesaw mechanisms.
Both are highly predictive so that in both the light neutrino sector
effectively depends only on three mass parameters and one Majorana phase, with
no CP violation in neutrino oscillations. We find that the linear seesaw leads
to a lower bound for neutrinoless double beta decay while the inverse seesaw
does not. The models also lead to potentially sizeable decay rates for lepton
flavor violating processes, tightly related by the assumed flavor symmetry.Comment: 8 pages, 3 figures. Experimental references added and figure 1
update
New Signatures for a Light Stop at LEP2 in SUSY Models with Spontaneously Broken R-Parity
In a class of supersymmetric models with R-parity breaking the lightest stop
can have new decay modes into third generation fermions, . We show that this decay may be dominant or at least
comparable to the ordinary R-parity conserving mode , where denotes the lightest neutralino.
The new R-parity violating decay mode could provide new signatures for stop
production at LEP.Comment: uudecoded latex file, 12 pages with 3 figures included. The complete
uudecoded ps paper is also available via anonymous ftp at
ftp://neutrinos.uv.es/pub/papers/ps/stop1.u
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