393 research outputs found
Production of doubly charged scalars from the decay of singly charged scalars in the Higgs Triplet Model
The existence of doubly charged Higgs bosons (H^{\pm\pm}) is a distinctive
feature of the Higgs Triplet Model (HTM), in which neutrinos obtain tree-level
masses from the vacuum expectation value of a neutral scalar in a triplet
representation of SU(2)_L. We point out that a large branching ratio for the
decay of a singly charged Higgs boson to a doubly charged Higgs boson via
H^\pm\to H^{\pm\pm}W^* is possible in a sizeable parameter space of the HTM.
From the production mechanism q'qbar\to W^* \to H^{\pm\pm}H^\mp the above decay
mode would give rise to pair production of H^{\pm\pm}, with a cross section
which can be comparable to that of the standard pair-production mechanism
qqbar\to \gamma^*,Z^* \to H^{++}H^{--}. We suggest that the presence of a
sizeable branching ratio for H^\pm\to H^{\pm\pm}W^* could significantly enhance
the detection prospects of H^{\pm\pm} in the four-lepton channel. Moreover, the
decays H^0\to H^\pm W^* and A^0\to H^\pm W^* from production of the neutral
triplet scalars H^0 and A^0 would also provide an additional source of H^\pm,
which can subsequently decay to H^{\pm\pm}.Comment: 13 pages, 3 figures, two figures added in v2, to appear in Physical
Review
On Probing theta_{23} in Neutrino Telescopes
Among all neutrino mixing parameters, the atmospheric neutrino mixing angle
theta_{23} introduces the strongest variation on the flux ratios of ultra high
energy neutrinos. We investigate the potential of these flux ratio measurements
at neutrino telescopes to constrain theta_{23}. We consider astrophysical
neutrinos originating from pion, muon-damped and neutron sources and make a
comparative study of their sensitivity reach to theta_{23}. It is found that
neutron sources are most favorable for testing deviations from maximal
theta_{23}. Using a chi^2 analysis, we show in particular the power of
combining (i) different flux ratios from the same type of source, and also (ii)
combining flux ratios from different astrophysical sources. We include in our
analysis ``impure'' sources, i.e., deviations from the usually assumed initial
(1 : 2 : 0), (0 : 1 : 0) or (1 : 0 : 0) flux compositions.Comment: 17 pages, 5 figures. Added discussion on experimental errors. To
appear in PR
Leptonic CP Violation Search and the Ambiguity of dm^2_31
We consider a search for the CP-violating angle deltaCP in long baseline
neutrino oscillation experiments. We show that the subleading deltaCP-dependent
terms in the nu_mu -> nu_e oscillation probability can be easily obscured by
the ambiguity of the leading term which depends on |dm^2_31|. It is thus
necessary to determine the value of dm^2_31 with a sufficient accuracy. The
nu_mu survival events, which can be accumulated simultaneously with the nu_e
appearance events, can serve for this purpose owing to its large statistics.
Therefore, the combined analysis of nu_e appearance and nu_mu survival events
is crucial to provide a restrictive constraint on deltaCP. Taking a test
experimental setup, we demonstrate in the deltaCP-dm^2_31 plane that the
analysis of nu_e appearance events leads to less restrictive constraints on the
value of deltaCP due to the ambiguity of dm^2_31 and that the combined analysis
efficiently improves the constraints.Comment: ReVTeX file, 9 pages, 7 figures. Discussions added in Sections 1, 2,
and 4; Reference expande
Probing Majorana neutrinos in rare K and D, D_s, B, B_c meson decays
We study lepton number violating decays of charged K, D, D_s, B and B_c
mesons of the form M^+\to {M'}^-\ell^+\ell^+, induced by the existence of
Majorana neutrinos. These processes provide information complementary to
neutrinoless double nuclear beta decays, and are sensitive to neutrino masses
and lepton mixing. We explore neutrino mass ranges m_N from below 1 eV to
several hundred GeV. We find that in many cases the branching ratios are
prohibitively small, however in the intermediate range m_\pi < m_N < m_{B_c},
in specific channels and for specific neutrino masses, the branching ratios can
be at the reach of high luminosity experiments like those at the LHC-b and
future Super flavor-factories, and can provide bounds on the lepton mixing
parameters.Comment: 25 page
Berry Phase in Neutrino Oscillations
We study the Berry phase in neutrino oscillations for both Dirac and Majorana
neutrinos. In order to have a Berry phase, the neutrino oscillations must occur
in a varying medium, the neutrino-background interactions must depend on at
least two independent densities, and also there must be CP violation if the
neutrino interactions with matter are mediated only by the standard model W and
Z boson exchanges which implies that there must be at least three generations
of neutrinos. The CP violating Majorana phases do not play a role in generating
a Berry phase. We show that a natural way to satisfy the conditions for the
generation of a Berry phase is to have sterile neutrinos with active-sterile
neutrino mixing, in which case at least two active and one sterile neutrinos
are required. If there are additional new CP violating flavor changing
interactions, it is also possible to have a non-zero Berry phase with just two
generations.Comment: RevTex 16 pages, no figures, new discussions about sterile neutrino
added,typos corrected and errors in references correcte
Reanalysis of the GALLEX solar neutrino flux and source experiments
After the completion of the gallium solar neutrino experiments at the
Laboratori Nazionali del Gran Sasso (GALLEX}: 1991-1997; GNO: 1998-2003) we
have retrospectively updated the GALLEX results with the help of new technical
data that were impossible to acquire for principle reasons before the
completion of the low rate measurement phase (that is, before the end of the
GNO solar runs). Subsequent high rate experiments have allowed the calibration
of absolute internal counter efficiencies and of an advanced pulse shape
analysis for counter background discrimination. The updated overall result for
GALLEX (only) is (73.4 +7.1 -7.3) SNU. This is 5.3% below the old value of
(77.5 + 7.5 -7.8) SNU (PLB 447 (1999) 127-133) with a substantially reduced
error. A similar reduction is obtained from the reanalysis of the 51Cr neutrino
source experiments of 1994/1995.Comment: Accepted by Physics Letters B January 13, 201
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