1,746 research outputs found
Neutrino Large Mixing in Universal Yukawa Coupling Model with Small Violation
We have analyzed the possibility that the universal Yukawa coupling
(democratic mass matrix) with small violations of Dirac and Majorana neutrinos
can induce the large mixing of neutrinos through the seesaw mechanism. The
possibility can be achieved by the condition that the violation parameters of
Majorana neutrinos are sufficiently smaller than the violation parameters of
Dirac neutrinos. Allowed regions of the violation parameters producing the
observed neutrino mass hierarchy and large neutrino mixing are not so
restricted at present in contrast to the violation parameters for quark sector.Comment: 14 pages, 4figure
Mixing among light scalar mesons and L=1 q\bar{q} scalar mesons
Following the re-establishment of the \sigma(600) and the \kappa(900), the
light scalar mesons a_0(980) and f_0(980) together with the \sigma(600) and the
\kappa(900) are considered as the chiral scalar partner of pseudoscalar nonet
in SU(3) chiral symmetry, and the high mass scalar mesons a_0(1450),
K^*_0(1430), f_0(1370) and f_0(1710) turned out to be considered as the L=1
q\bar{q} scalar mesons. We assume that the high mass of the L=1 q\bar{q} scalar
mesons is caused by the mixing with the light scalar mesons. For the structure
of the light scalar mesons, we adopted the qq\bar{q}\bar{q} model in order to
explain the "scalar meson puzzle". The inter-mixing between the light scalar
nonet and the high mass L=1 q\bar{q} nonet and the intra-mixing among each
nonet are analyzed by including the glueball into the high mass scalar nonet.Comment: 16 pages, 5 figure
Measurement of energy muons in EAS at energy region larger thean 10(17) eV
A measurement of low energy muons in extensive air showers (EAS) (threshold energies are 0.25, 0.5, 0.75 and 1.38 GeV) was carried out. The density under the concrete shielding equivalent to 0.25 GeV at core distance less than 500 m and 0.5 GeV less than 150 m suffers contamination of electromagnetic components. Therefore the thickness of concrete shielding for muon detectors for the giant air shower array is determined to be 0.5 GeV equivalence. Effects of photoproduced muons are found to be negligible in the examined ranges of shower sizes and core distances. The fluctuation of the muon density in 90 sq m is at most 25% between 200 m and 600 m from the core around 10 to the 17th power eV
Study of the performance and capability of the new ultra-fast 2 GSample/s FADC data acquisition system of the MAGIC telescope
In February 2007 the MAGIC Air Cherenkov Telescope for gamma-ray astronomy
was fully upgraded with an ultra fast 2 GSamples/s digitization system. Since
the Cherenkov light flashes are very short, a fast readout can minimize the
influence of the background from the light of the night sky. Also, the time
structure of the event is an additional parameter to reduce the background from
unwanted hadronic showers. An overview of the performance of the new system and
its impact on the sensitivity of the MAGIC instrument will be presented.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of
the MAGIC Collaboratio
Wide-Area Mapping of 155 Micron Continuum Emission from the Orion Molecular Cloud Complex
We present the results of a wide-area mapping of the far-infrared continuum
emission toward the Orion complex by using a Japanese balloon-borne telescope.
The 155-um continuum emission was detected over a region of 1.5 deg^2 around
the KL nebula with 3' resolution similar to that of the IRAS 100-um map.
Assuming a single-temperature model of the thermal equilibrium dust, maps of
the temperature and the optical depth were derived from the 155 um intensity
and the IRAS 100 um intensity. The derived dust temperature is 5 - 15 K lower
and the derived dust optical thickness were derived from the 155-um intensity
and the IRAS 100-um intensity. The derived dust temperature is 5 - 15 K lower
and the derived dust optical depth is 5 - 300 times larger than those derived
from the IRAS 60 and 100-um intensities due to the significant contribution of
the statistically heated very small grains to the IRAS 60-um intensity. The
optical-thickness distribution shows a filamentary dust ridge that has a 1.5
degrees extent in the north - south direction and well resembles the
Integral-Shaped Filament (ISF) molecular gas distribution. The gas-to-dust
ratio derived from the CO molecular gas distribution along the ISF is in the
range 30 - 200, which may be interpreted as being an effect of CO depletion due
to the photodissociation and/or the freezing on dust grains.Comment: 23 pages, 7 figures, 1 table, to appear in PASJ, Vol. 56, No.
Akeno 20 km (2) air shower array (Akeno Branch)
As the first stage of the future huge array, the Akeno air shower array was expanded to about 20 sq. km. by adding 19 scintillation detectors of 2.25 sq m area outside the present 1 sq. km. Akeno array with a new data collection system. These detectors are spaced about 1km from each other and connected by two optical fiber cables. This array has been in partial operation from 8th, Sep. 1984 and full operation from 20th, Dec. 1984. 20 sq m muon stations are planned to be set with 2km separation and one of them is now under construction. The origin of the highest energy cosmic rays is studied
Bi-large Neutrino Mixing and Mass of the Lightest Neutrino from Third Generation Dominance in a Democratic Approach
We show that both small mixing in the quark sector and large mixing in the
lepton sector can be obtained from a simple assumption of universality of
Yukawa couplings and the right-handed neutrino Majorana mass matrix in leading
order. We discuss conditions under which bi-large mixing in the lepton sector
is achieved with a minimal amount of fine-tuning requirements for possible
models. From knowledge of the solar and atmospheric mixing angles we determine
the allowed values of sin \theta_{13}. If embedded into grand unified theories,
the third generation Yukawa coupling unification is a generic feature while
masses of the first two generations of charged fermions depend on small
perturbations. In the neutrino sector, the heavier two neutrinos are model
dependent, while the mass of the lightest neutrino in this approach does not
depend on perturbations in the leading order. The right-handed neutrino mass
scale can be identified with the GUT scale in which case the mass of the
lightest neutrino is given as (m_{top}^2/M_{GUT}) sin^2 \theta_{23} sin^2
\theta_{12} in the limit sin \theta_{13} = 0. Discussing symmetries we make a
connection with hierarchical models and show that the basis independent
characteristic of this scenario is a strong dominance of the third generation
right-handed neutrino, M_1, M_2 < 10^{-4} M_3, M_3 = M_{GUT}.Comment: typos correcte
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