2,059 research outputs found
Classical XY Model in 1.99 Dimensions
We consider the classical XY model (O(2) nonlinear sigma-model) on a class of
lattices with the (fractal) dimensions 1<D<2. The Berezinskii's harmonic
approximation suggests that the model undergoes a phase transition in which the
low temperature phase is characterized by stretched exponential decay of
correlations. We prove an exponentially decaying upper bound for the two-point
correlation functions at non-zero temperatures, thus excluding the possibility
of such a phase transition.Comment: LaTeX 8 pages, no figure
First Experimental Characterization of Microwave Emission from Cosmic Ray Air Showers
We report the first direct measurement of the overall characteristics of
microwave radio emission from extensive air showers. Using a trigger provided
by the KASCADE-Grande air shower array, the signals of the microwave antennas
of the CROME (Cosmic-Ray Observation via Microwave Emission) experiment have
been read out and searched for signatures of radio emission by high-energy air
showers in the GHz frequency range. Microwave signals have been detected for
more than 30 showers with energies above 3*10^16 eV. The observations presented
in this Letter are consistent with a mainly forward-directed and polarised
emission process in the GHz frequency range. The measurements show that
microwave radiation offers a new means of studying air showers at energies
above 10^17 eV.Comment: Accepted for publication in PR
POET: POlarimeters for Energetic Transients
POET (Polarimeters for Energetic Transients) is a Small Explorer mission
concept proposed to NASA in January 2008. The principal scientific goal of POET
is to measure GRB polarization between 2 and 500 keV. The payload consists of
two wide FoV instruments: a Low Energy Polarimeter (LEP) capable of
polarization measurements in the energy range from 2-15 keV and a high energy
polarimeter (Gamma-Ray Polarimeter Experiment -- GRAPE) that will measure
polarization in the 60-500 keV energy range. Spectra will be measured from 2
keV up to 1 MeV. The POET spacecraft provides a zenith-pointed platform for
maximizing the exposure to deep space. Spacecraft rotation will provide a means
of effectively dealing with systematics in the polarization response. POET will
provide sufficient sensitivity and sky coverage to measure statistically
significant polarization for up to 100 GRBs in a two-year mission. Polarization
data will also be obtained for solar flares, pulsars and other sources of
astronomical interest
Energy Spectra of Elemental Groups of Cosmic Rays: Update on the KASCADE Unfolding Analysis
The KASCADE experiment measures extensive air showers induced by cosmic rays
in the energy range around the so-called knee. The data of KASCADE have been
used in a composition analysis showing the knee at 3-5 PeV to be caused by a
steepening in the light-element spectra. Since the applied unfolding analysis
depends crucially on simulations of air showers, different high energy hadronic
interaction models (QGSJet and SIBYLL) were used. The results have shown a
strong dependence of the relative abundance of the individual mass groups on
the underlying model. In this update of the analysis we apply the unfolding
method with a different low energy interaction model (FLUKA instead of GHEISHA)
in the simulations. While the resulting individual mass group spectra do not
change significantly, the overall description of the measured data improves by
using the FLUKA model. In addition data in a larger range of zenith angle are
analysed. The new results are completely consistent, i.e. there is no hint to
any severe problem in applying the unfolding analysis method to KASCADE data.Comment: accepted for publication in Astroparticle Physic
KCDC - The KASCADE Cosmic-ray Data Centre
KCDC, the KASCADE Cosmic-ray Data Centre, is a web portal, where data of
astroparticle physics experiments will be made available for the interested
public. The KASCADE experiment, financed by public money, was a large-area
detector for the measurement of high-energy cosmic rays via the detection of
air showers. KASCADE and its extension KASCADE-Grande stopped finally the
active data acquisition of all its components including the radio EAS
experiment LOPES end of 2012 after more than 20 years of data taking. In a
first release, with KCDC we provide to the public the measured and
reconstructed parameters of more than 160 million air showers. In addition,
KCDC provides the conceptional design, how the data can be treated and
processed so that they are also usable outside the community of experts in the
research field. Detailed educational examples make a use also possible for
high-school students and early stage researchers.Comment: 8 pages, accepted proceeding of the ECRS-symposium, Kiel, 201
- …