1,263 research outputs found
Cherenkov Telescope Array: The next-generation ground-based gamma-ray observatory
High energy gamma-ray astronomy is a newly emerging and very successful
branch of astronomy and astrophysics. Exciting results have been obtained by
the current generation Cherenkov telescope systems such as H.E.S.S., MAGIC,
VERITAS and CANGAROO. The H.E.S.S. survey of the galactic plane has revealed a
large number of sources and addresses issues such as the question about the
origin of cosmic rays. The detection of very high energy emission from
extragalactic sources at large distances has provided insights in the star
formation during the history of the universe and in the understanding of active
galactic nuclei. The development of the very large Cherenkov telescope array
system (CTA) with a sensitivity about an order of magnitude better than current
instruments and significantly improved sensitivity is under intense discussion.
This observatory will reveal an order of magnitude more sources and due to its
higher sensitivity and angular resolution it will be able to detect new classes
of objects and phenomena that have not been visible until now. A combination of
different telescope types will provide the sensitivity needed in different
energy ranges.Comment: 4 pages, 3 figures, to appear in the proceedings of the 30th
International Cosmic Ray Conference, Merida, July 200
How many electrons are needed to flip a local spin?
Considering the spin of a local magnetic atom as a quantum mechanical
operator, we illustrate the dynamics of a local spin interacting with a
ballistic electron represented by a wave packet. This approach improves the
semi-classical approximation and provides a complete quantum mechanical
understanding for spin transfer phenomena. Sending spin-polarized electrons
towards a local magnetic atom one after another, we estimate the minimum number
of electrons needed to flip a local spin.Comment: 3 figure
Complete Genome Sequence of Clostridium clariflavum DSM 19732
Clostridium clariflavum is a Cluster III Clostridium within the family Clostridiaceae isolated from thermophilic anaerobic sludge (Shiratori et al, 2009). This species is of interest because of its similarity to the model cellulolytic organism Clostridium thermocellum and for the ability of environmental isolates to break down cellulose and hemicellulose. Here we describe features of the 4,897,678 bp long genome and its annotation, consisting of 4,131 protein-coding and 98 RNA genes, for the type strain DSM 19732
Long term monitoring of bright TeV Blazars with the MAGIC telescope
The MAGIC telescope has performed long term monitoring observations of the
bright TeV Blazars Mrk421, Mrk501 and 1ES1959+650. Up to 40 observations, 30 to
60 minutes each have been performed for each source evenly distributed over the
observable period of the year. The sensitivity of MAGIC is sufficient to
establish a flux level of 25% of the Crab flux for each measurement. These
observations are well suited to trigger multiwavelength ToO observations and
the overall collected data allow an unbiased study of the flaring statistics of
the observed AGNs.Comment: 4 pages, 4 figures, to appear in the proceedings of the 30th
International Cosmic Ray Conference, Merida, July 200
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
Neutrino Mass and Oscillation
The question of neutrino mass is one of the major riddles in particle
physics. Recently, strong evidence that neutrinos have nonzero masses has been
found. While tiny, these masses could be large enough to contribute
significantly to the mass density of the universe. The evidence for
nonvanishing neutrino masses is based on the apparent observation of neutrino
oscillation -- the transformation of a neutrino of one type or "flavor" into
one of another. We explain the physics of neutrino oscillation, and review and
weigh the evidence that it actually occurs in nature. We also discuss the
constraints on neutrino mass from cosmology and from experiments with negative
results. After presenting illustrative neutrino mass spectra suggested by the
present data, we consider how near- and far-future experiments can further
illuminate the nature of neutrinos and their masses.Comment: 43 pages, 8 figures, to appear in the Annual Review of Nuclear and
Particle Science, Vol. 49 (1999
Small Scale Anisotropy Predictions for the Auger Observatory
We study the small scale anisotropy signal expected at the Pierre Auger
Observatory in the next 1, 5, 10, and 15 years of operation, from sources of
ultra-high energy (UHE) protons. We numerically propagate UHE protons over
cosmological distances using an injection spectrum and normalization that fits
current data up to \sim 10^{20}\eV. We characterize possible sources of
ultra-high energy cosmic rays (UHECRs) by their mean density in the local
Universe, Mpc, with between 3 and 6.
These densities span a wide range of extragalactic sites for UHECR sources,
from common to rare galaxies or even clusters of galaxies. We simulate 100
realizations for each model and calculate the two point correlation function
for events with energies above 4 \times 10^{19}\eV and above 10^{20}\eV, as
specialized to the case of the Auger telescope. We find that for r\ga 4,
Auger should be able to detect small scale anisotropies in the near future.
Distinguishing between different source densities based on cosmic ray data
alone will be more challenging than detecting a departure from isotropy and is
likely to require larger statistics of events. Combining the angular
distribution studies with the spectral shape around the GZK feature will also
help distinguish between different source scenarios.Comment: 15 pages, 6 figures, 6 tables, submitted to JCA
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