751 research outputs found
Global oscillation analysis of solar neutrino data with helioseismically constrained fluxes
A seismic model for the Sun calculated using the accurate helioseismic data
predicts a lower neutrino flux as compared to the standard solar
model (SSM). However, there persists a discrepancy between the predicted and
measured neutrino fluxes and it seems necessary to invoke neutrino oscillations
to explain the measurements. In this work, we have performed a global, unified
oscillation analysis of the latest solar neutrino data (including the results
of SNO charged current rate) using the seismic model fluxes as theoretical
predictions. We determine the best-fit values of the neutrino oscillation
parameters and the for both
and cases and present the allowed parameter
regions in the plane for transition. The results are compared with those obtained using the
latest SSM by Bahcall and his collaborators.Comment: Version to appear in Phys. Rev.
Universality of scanning tunneling microscopy in cuprate superconductors
We consider the problem of local tunneling into cuprate superconductors,
combining model based calculations for the superconducting order parameter with
wavefunction information obtained from first principles electronic structure.
For some time it has been proposed that scanning tunneling microscopy (STM)
spectra do not reflect the properties of the superconducting layer in the
CuO plane directly beneath the STM tip, but rather a weighted sum of
spatially proximate states determined by the details of the tunneling process.
These "filter" ideas have been countered with the argument that similar
conductance patterns have been seen around impurities and charge ordered states
in systems with atomically quite different barrier layers. Here we use a
recently developed Wannier function based method to calculate topographies,
spectra, conductance maps and normalized conductance maps close to impurities.
We find that it is the local planar Cu Wannier function,
qualitatively similar for many systems, that controls the form of the tunneling
spectrum and the spatial patterns near perturbations. We explain how, despite
the fact that STM observables depend on the materials-specific details of the
tunneling process and setup parameters, there is an overall universality in the
qualitative features of conductance spectra. In particular, we discuss why STM
results on BiSrCaCuO and CaNaCuOCl are
essentially identical
Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates
We apply a recently developed method combining first principles based Wannier
functions with solutions to the Bogoliubov-de Gennes equations to the problem
of interpreting STM data in cuprate superconductors. We show that the observed
images of Zn on the surface of BiSrCaCuO can only be understood
by accounting for the tails of the Cu Wannier functions, which include
significant weight on apical O sites in neighboring unit cells. This
calculation thus puts earlier crude "filter" theories on a microscopic
foundation and solves a long standing puzzle. We then study quasiparticle
interference phenomena induced by out-of-plane weak potential scatterers, and
show how patterns long observed in cuprates can be understood in terms of the
interference of Wannier functions above the surface. Our results show excellent
agreement with experiment and enable a better understanding of novel phenomena
in the cuprates via STM imaging.Comment: 5 pages, 5 figures, published version (Supplemental Material: 5
pages, 11 figures) for associated video file, see
http://itp.uni-frankfurt.de/~kreisel/QPI_BSCCO_BdG_p_W.mp
Neutrino parameters from matter effects in at long baselines
We show that the earth matter effects in the
survival probability can be used to cleanly determine the third leptonic mixing
angle and the sign of the atmospheric neutrino mass squared
difference, , using a -beam as a source.Comment: 4 pages, 4 eps figures; comments and references added, to appear in
Phys. Rev.
Confusing Sterile Neutrinos with Deviation from Tribimaximal Mixing at Neutrino Telescopes
We expound the impact of extra sterile species on the ultra high energy
neutrino fluxes in neutrino telescopes. We use three types of well-known flux
ratios and compare the values of these flux ratios in presence of sterile
neutrinos, with those predicted by deviation from the tribimaximal mixing
scheme. We show that in the upcoming neutrino telescopes, its easy to confuse
between the signature of sterile neutrinos with that of the deviation from
tribimaximal mixing. We also show that if the measured flux ratios acquire a
value well outside the range predicted by the standard scenario with three
active neutrinos only, it might be possible to tell the presence of extra
sterile neutrinos by observing ultra high energy neutrinos in future neutrino
telescopes.Comment: 22 pages, version to appear in Phys. Rev.
Turbulent Supernova Shock Waves and the Sterile Neutrino Signature in Megaton Water Detectors
The signatures of sterile neutrinos in the supernova neutrino signal in
megaton water Cerenkov detectors are studied. Time dependent modulation of the
neutrino signal emerging from the sharp changes in the oscillation probability
due to shock waves is shown to be a smoking gun for the existence of sterile
neutrinos. These modulations and indeed the entire neutrino oscillation signal
is found to be different for the case with just three active neutrinos and the
cases where there are additional sterile species mixed with the active
neutrinos. The effect of turbulence is taken into account and it is found that
the effect of the shock waves, while modifed, remain significant and
measurable. Supernova neutrino signals in water detectors can therefore give
unambiguous proof for the existence of sterile neutrinos, the sensitivity
extending beyond that for terrestial neutrino experiments. In addition the time
dependent modulations in the signal due to shock waves can be used to trace the
evolution of the shock wave inside the supernova.Comment: 28 pages, 11 figure
Three Generation Neutrino Oscillation Parameters after SNO
We examine the solar neutrino problem in the context of the realistic three
neutrino mixing scenario including the SNO charged current (CC) rate. The two
independent mass squared differences and are taken to be in the solar and atmospheric ranges
respectively. We incorporate the constraints on m as obtained
by the SuperKamiokande atmospheric neutrino data and determine the allowed
values of , and from a combined
analysis of solar and CHOOZ data. Our aim is to probe the changes in the values
of the mass and mixing parameters with the inclusion of the SNO data as well as
the changes in the two-generation parameter region obtained from the solar
neutrino analysis with the inclusion of the third generation. We find that the
inclusion of the SNO CC rate in the combined solar + CHOOZ analysis puts a more
restrictive bound on . Since the allowed values of
are constrained to very small values by the CHOOZ experiment there is no
qualitative change over the two generation allowed regions in the plane. The best-fit comes in the LMA region and
no allowed area is obtained in the SMA region at 3 level from combined
solar and CHOOZ analysis.Comment: One reference added. Version to apprear in PR
Hadron energy response of the Iron Calorimeter detector at the India-based Neutrino Observatory
The results of a Monte Carlo simulation study of the hadron energy response
for the magnetized Iron CALorimeter detector, ICAL, proposed to be located at
the India-based Neutrino Observatory (INO) is presented. Using a GEANT4
modeling of the detector ICAL, interactions of atmospheric neutrinos with
target nuclei are simulated. The detector response to hadrons propagating
through it is investigated using the hadron hit multiplicity in the active
detector elements. The detector response to charged pions of fixed energy is
studied first, followed by the average response to the hadrons produced in
atmospheric neutrino interactions using events simulated with the NUANCE event
generator. The shape of the hit distribution is observed to fit the Vavilov
distribution, which reduces to a Gaussian at high energies. In terms of the
parameters of this distribution, we present the hadron energy resolution as a
function of hadron energy, and the calibration of hadron energy as a function
of the hit multiplicity. The energy resolution for hadrons is found to be in
the range 85% (for 1GeV) -- 36% (for 15 GeV).Comment: 14 pages, 10 figures (24 eps files
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