3,958 research outputs found
Low scale B-L extension of the Standard Model at the LHC
The fact that neutrinos are massive indicates that the Standard Model (SM)
requires extension. We propose a low energy (<TeV) B-L extension of the SM,
which is based on the gauge group SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}. We
show that this model provides a natural explanation for the presence of three
right-handed neutrinos in addition to an extra gauge boson and a new scalar
Higgs. Therefore, it can lead to very interesting phenomenological implications
different from the SM results which can be tested at the LHC. Also we analyze
the muon anomalous magnetic moment in this class of models. We show that
one-loop with exchange Z' may give dominant new contribution ~ few x 10^{-11}.Comment: 12 page
Neutrino mixing and CP violation from Dirac-Majorana bimaximal mixture and quark-lepton unification
We demonstrate that only two ansatz can produce the features of the neutrino
mixing angles. The first ansatz comes from the quark-lepton grand unification;
is satisfied for left-handed neutrinos, where
are the Dirac mass eigenstates and are the flavour
eigenstates. The second ansatz comes from the assumption; is satisfied between the Dirac mass eigenstates
and the light Majorana neutrino mass eigenstates , where
is the bimaximal mixing matrix. By these two ansatz, the
Maki-Nakagawa-Sakata matrix is given by . We find that in this model the novel relation is satisfied, where and are
solar and CHOOZ angle respectively. This "Solar-CHOOZ Complementarity" relation
indicates that only if the CHOOZ angle is sizable, the solar
angle can deviate from the maximal mixing. We also infer the CP
violation in neutrino oscillations. The leptonic Dirac CP phase
is predicted as , where are the CKM parameters in Wolfenstein parametrization. Furthermore, we
remark that the ratio of the Jarlskog CP violation factor for quarks and
leptons is important, because the large uncertainty on is cancelled out
in the ratio, .Comment: 9 pages, no figures; v2 references added, v3 references adde
Off-diagonal structure of neutrino mass matrix in see-saw mechanism and electron-muon-tau lepton universality
By a simple extension of the standard model in which ()
universality is not conserved, we present a scenario within the framework of
see-saw mechanism in which the neutrino mass matrix is strictly off-diagonal in
the flavor basis. We show that a version of this scenario can accomodate the
atmospheric neutrino oscillations and
oscillations claimed by the LSND collaboration.
PACS: 14.60.Pq; 14.60.St;13.15.+gComment: 5 pages, Revtex, 1 figure: The model accomodate another version which
explains atmospheric neutrino data and the observed solar neutrino
oscillations (large angle solution). In the previous version the value of
\lambda parameter is changed to the expected one. This version now
accomodates LSND result and solar neutrino oscillations (small angle MSW
solution
Neutrino Mass and Grand Unification
Seesaw mechanism appears to be the simplest and most appealing way to
understand small neutrino masses observed in recent experiments. It introduces
three right handed neutrinos with heavy masses to the standard model, with at
least one mass required by data to be close to the scale of conventional grand
unified theories. This may be a hint that the new physics scale implied by
neutrino masses and grand unification of forces are one and the same. Taking
this point of view seriously, I explore different ways to resolve the puzzle of
large neutrino mixings in grand unified theories such as SO(10) and models
based on its subgroup .Comment: 17 pages, 5 figures; Invited talk at the Nobel Symposium 129 on
Neutrinos at Haga Slott, Sweden, August, 200
Neutrino Mixing and Neutrino Telescopes
Measuring flux ratios of ultra-high energy neutrinos is an alternative method
to determine the neutrino mixing angles and the CP phase delta. We conduct a
systematic analysis of the neutrino mixing probabilities and of various flux
ratios measurable at neutrino telescopes. The considered cases are neutrinos
from pion, neutron and muon-damped sources. Explicit formulae in case of mu-tau
symmetry and its special case tri-bimaximal mixing are obtained, and the
leading corrections due to non-zero theta_{13} and non-maximal theta_{23} are
given. The first order correction is universal as it appears in basically all
ratios. We study in detail its dependence on theta_{13}, theta_{23} and the CP
phase, finding that the dependence on theta_{23} is strongest. The flavor
compositions for the considered neutrino sources are evaluated in terms of this
correction. A measurement of a flux ratio is a clean measurement of the
universal correction (and therefore of theta_{13}, theta_{23} and delta) if the
zeroth order ratio does not depend on theta_{12}. This favors pion sources over
the other cases, which in turn are good candidates to probe theta_{12}. The
only situations in which the universal correction does not appear are certain
ratios in case of a neutron and muon-damped source, which depend mainly on
theta_{12} and receive only quadratic corrections from the other parameters. We
further show that there are only two independent neutrino oscillation
probabilities, give the allowed ranges of the considered flux ratios and of all
probabilities, and show that none of the latter can be zero or one.Comment: 29 pages, 8 figures. Minor changes, to appear in JCA
Lepton Flavor Violating Z Decays in the Zee Model
We calculate lepton flavor violating (LFV) Z decays Z \to {{e_i^\pm}}e_j^\mp
(i, j = e, \mu, \tau ; i\neq j) in the Zee model keeping in view the radiative
leptonic decays e_i\to e_j\gamma (i = \mu, \tau ; j = e, \mu ; i\neq j), \mu
decay and anomalous muon magnetic moment (\mu AMM). We investigate three
different cases of Zee f_{ij} coupling (A) f_{e\mu}^2 = f_{\mu\tau}^2= f_{\tau
e}^2, (B) f_{e\mu}^2 \gg f_{\tau e}^2 \gg f_{\mu\tau}^2, and (C) f_{\mu\tau}^2
\gg f_{e\mu}^2 \gg f_{\tau e}^2 subject to the neutrino phenomenology.
Interestingly, we find that, although the case (C) satisfies the large excess
value of \mu AMM, however, it is unable to explain the solar neutrino
experimental result, whereas the case (B) satisfies the bi-maximal neutrino
mixing scenario, but confronts with the result of \mu AMM experiment. We also
find that among all the three cases, only the case (C) gives rise to largest
contribution to the ratio B(Z\to e^\pm\tau^\mp)/B(Z\to \mu^\pm \mu^\mp) \simeq
{10}^{-8} which is still two order less than the accessible value to be probed
by the future linear colliders, whereas for the other two cases, this ratio is
too low to be observed even in the near future for all possible LFV Z decay
modes.Comment: 12 pages, RevTex, 2 figures, 3 Tables, typos corrected, reference
added, version to appear in Phys. Rev.
Theta-13 as a Probe of Mu-Tau symmetry for Leptons
Many experiments are being planned to measure the neutrino mixing parameter
using reactor as well as accelerator neutrino beams. In this
note, the theoretical significance of a high precision measurement of this
parameter is discussed. It is emphasized that it will provide crucial
information about different ways to understand the origin of large atmospheric
neutrino mixing and move us closer towards determining the neutrino mass
matrix. For instance if exact symmetry in the
neutrino mass matrix is assumed to be the reason for maximal
mixing, one gets . Whether or can provide information about the way the
symmetry breaking manifests in the case of normal hierarchy. We also discuss
the same question for inverted hierarchy as well as possible gauge theories
with this symmetry.Comment: 12 pages; no figures; latex; more exact expressions given for some
parameters and minor typos corrected; paper accepted for publication in JHE
Neutrino anomalies and large extra dimensions
Theories with large extra dimensions can generate small neutrino masses when
the standard model neutrinos are coupled to singlet fermions propagating in
higher dimensions. The couplings can also generate mass splittings and mixings
among the flavour neutrinos in the brane. We systematically study the minimal
scenario involving only one singlet bulk fermion coupling weakly to the flavour
neutrinos. We explore the neutrino mass structures in the brane that can
potentially account for the atmospheric, solar and LSND anomalies
simultaneously in a natural way. We demonstrate that in the absence of a priori
mixings among the SM neutrinos, it is not possible to reconcile all these
anomalies. The presence of some structure in the mass matrix of the SM
neutrinos can solve this problem. This is exemplified by the Zee model, which
when embedded in extra dimensions in a minimal way can account for all the
neutrino anomalies.Comment: 23 Revtex pages with 2 eps figure
Mass Hierarchies and the Seesaw Neutrino Mixing
We give a general analysis of neutrino mixing in the seesaw mechanism with
three flavors. Assuming that the Dirac and u-quark mass matrices are similar,
we establish simple relations between the neutrino parameters and individual
Majorana masses. They are shown to depend rather strongly on the physical
neutrino mixing angles. We calculate explicitly the implied Majorana mass
hierarchies for parameter sets corresponding to different solutions to the
solar neutrino problem.Comment: 11 pages, no figures, replaced with final version. Minor corrections
and one typo corrected. Added one referenc
Minimal SUSY SO(10) model and predictions for neutrino mixings and leptonic CP violation
We discuss a minimal Supersymmetric SO(10) model where B-L symmetry is broken
by a {\bf 126} dimensional Higgs multiplet which also contributes to fermion
masses in conjunction with a {\bf 10} dimensional superfield. This minimal
Higgs choice provides a partial unification of neutrino flavor structure with
that of quarks and has been shown to predict all three neutrino mixing angles
and the solar mass splitting in agreement with observations, provided one uses
the type II seesaw formula for neutrino masses. In this paper we generalize
this analysis to include arbitrary CP phases in couplings and vevs. We find
that (i) the predictions for neutrino mixings are similar with as before and other parameters in a somewhat bigger range and (ii) that
to first order in the quark mixing parameter (the Cabibbo angle), the
leptonic mixing matrix is CP conserving. We also find that in the absence of
any higher dimensional contributions to fermion masses, the CKM phase is
different from that of the standard model implying that there must be new
contributions to quark CP violation from the supersymmetry breaking sector.
Inclusion of higher dimensional terms however allows the standard model CKM
phase to be maintained.Comment: 22 pages, 6 figure
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