36 research outputs found
Flavor Ratios of Astrophysical Neutrinos: Implications for Precision Measurements
We discuss flavor-mixing probabilities and flavor ratios of high energy
astrophysical neutrinos. In the first part of this paper, we expand the
neutrino flavor-fluxes in terms of the small parameters U_{e3} and pi/4 -
theta_{23}, and show that there are universal first and second order
corrections. The second order term can exceed the first order term, and so
should be included in any analytic study. We also investigate the probabilities
and ratios after a further expansion around the tribimaximal value of sin^2
theta_{12} = 1/3. In the second part of the paper, we discuss implications of
deviations of initial flavor ratios from the usually assumed, idealized flavor
compositions for pion, muon-damped, and neutron beam sources, viz., (1 : 2 :
0), (0 : 1 : 0), and (1 : 0 : 0), respectively. We show that even small
deviations have significant consequences for the observed flavor ratios at
Earth. If initial flavor deviations are not taken into account in analyses,
then false inferences for the values in the PMNS matrix elements (angles and
phase) may result.Comment: 32 pages, 15 figures. Minor changes, matches version in JHE
Signature of sterile species in atmospheric neutrino data at neutrino telescopes
The MiniBooNE results have still not been able to comprehensively rule out
the oscillation interpretation of the LSND experiment. So far the so-called
short baseline experiments with energy in the MeV range and baseline of few
meters have been probing the existence of sterile neutrinos. We show how
signatures of these extra sterile states could be obtained in TeV energy range
atmospheric neutrinos travelling distances of thousands of kilometers.
Atmospheric neutrinos in the TeV range would be detected by the upcoming
neutrino telescopes. Of course vacuum oscillations of these neutrinos would be
very small. However, we show that resonant matter effects inside the Earth
could enhance these very tiny oscillations into near-maximal transitions, which
should be hard to miss. We show that imprint of sterile neutrinos could be
unambiguously obtained in this high energy atmospheric neutrino event sample.
Not only would neutrino telescopes tell the presence of sterile neutrinos, it
should also be possible for them to distinguish between the different possible
mass and mixing scenarios with additional sterile states.Comment: 26 pages, 11 figures, Version to appear in JHE
MiniBooNE Results and Neutrino Schemes with 2 sterile Neutrinos: Possible Mass Orderings and Observables related to Neutrino Masses
The MiniBooNE and LSND experiments are compatible with each other when two
sterile neutrinos are added to the three active ones. In this case there are
eight possible mass orderings. In two of them both sterile neutrinos are
heavier than the three active ones. In the next two scenarios both sterile
neutrinos are lighter than the three active ones. The remaining four scenarios
have one sterile neutrino heavier and another lighter than the three active
ones. We analyze all scenarios with respect to their predictions for
mass-related observables. These are the sum of neutrino masses as constrained
by cosmological observations, the kinematic mass parameter as measurable in the
KATRIN experiment, and the effective mass governing neutrinoless double beta
decay. It is investigated how these non-oscillation probes can distinguish
between the eight scenarios. Six of the eight possible mass orderings predict
positive signals in the KATRIN and future neutrinoless double beta decay
experiments. We also remark on scenarios with three sterile neutrinos. In
addition we make some comments on the possibility of using decays of high
energy astrophysical neutrinos to discriminate between the mass orderings in
presence of two sterile neutrinos.Comment: 33 pages, 8 figures. Comments added, to appear in JHE
Probing the Role of Magnetic-Field Variations in NOAA AR 8038 in Producing Solar Flare and CME on 12 May 1997
We carried out a multi-wavelength study of a CME and a medium-size 1B/C1.3
flare occurring on 12 May 1997. We present the investigation of magnetic-field
variations in the NOAA Active Region 8038 which was observed on the Sun during
7--16 May 1997. Analyses of H{\alpha} filtergrams and MDI/SOHO magnetograms
revealed continual but discrete surge activity, and emergence and cancellation
of flux in this active region. The movie of these magnetograms revealed two
important results that the major opposite polarities of pre-existing region as
well as in the emerging flux region (EFR) were approaching towards each other
and moving magnetic features (MMF) were ejecting out from the major north
polarity at a quasi-periodicity of about ten hrs during 10--13 May 1997. These
activities were probably caused by the magnetic reconnection in the lower
atmosphere driven by photospheric convergence motions, which were evident in
magnetograms. The magnetic field variations such as flux, gradient, and sunspot
rotation revealed that free energy was slowly being stored in the corona. The
slow low-layer magnetic reconnection may be responsible for this storage and
the formation of a sigmoidal core field or a flux rope leading to the eventual
eruption. The occurrence of EUV brightenings in the sigmoidal core field prior
to the rise of a flux rope suggests that the eruption was triggered by the
inner tether-cutting reconnection, but not the external breakout reconnection.
An impulsive acceleration revealed from fast separation of the H{\alpha}
ribbons of the first 150 seconds suggests the CME accelerated in the inner
corona, which is consistent with the temporal profile of the reconnection
electric field. In conclusion, we propose a qualitative model in view of
framework of a solar eruption involving, mass ejections, filament eruption,
CME, and subsequent flare.Comment: 8 figures, accepted for publication in Solar Physic
ICRAM (the international campaign to revitalise academic medicine): agenda setting
Following die launch by the BMJ and others of the campaign to promote academic medicine, a working party of 20 medical academics from all over the world was convened to develop a plan of action
Academic medicine: the evidence base
The International Campaign to Revitalise Academic Medicine recognises that an evidence based approach is important in discussing the problems of academic medicine. A preliminary exploration of the evidence on academic medicine has led to a research agenda for examining and proposing realistic solution