19 research outputs found
Charged Dust Particles in Interplanetary Space
Charged dust particles in interplanetary spac
Optical Properties of atmospheric dust from twilight observations
Three methods of approximation are described and used to separate the primary twilight brightness from the observed brightness. Photoelectric observations obtained are combined with observations from a balloon and from the observatory to derive the atmospheric scattering phase functions of 0.37 micron and 0.58 micron as a function of height. Comparison of these data with data for a Rayleigh atmosphere provide information on the optical properties of dust in the upper atmosphere
Isophots of Zodiacal Light and Its Terrestrial Component
Isophotes of zodiacal light and its terrestrial component due to interplanetary dust in vicinity of earth-moon syste
Localized Wavefunctions and Magnetic Band Structure for Lateral Semiconductor Superlattices
In this paper we present calculations on the electronic band structure of a
two-dimensional lateral superlattice subject to a perpendicular magnetic field
by employing a projection operator technique based on the ray-group of
magnetotranslation operators. We construct a new basis of appropriately
symmetrized Bloch-like wavefunctions as linear combination of well-localized
magnetic-Wannier functions. The magnetic field was consistently included in the
Wannier functions defined in terms of free-electron eigenfunctions in the
presence of external magnetic field in the symmetric gauge. Using the above
basis, we calculate the magnetic energy spectrum of electrons in a lateral
superlattice with bi-directional weak electrostatic modulation. Both a square
lattice and a triangular one are considered as special cases. Our approach
based on group theory handles the cases of integer and rational magnetic fluxes
in a uniform way and the provided basis could be convenient for further both
analytic and numerical calculations.Comment: 19 pages, 5 figures. accepted to Int. J. Mod. Phys. B (April 2006
Dark Matter Spin-Dependent Limits for WIMP Interactions on 19-F by PICASSO
The PICASSO experiment at SNOLAB reports new results for spin-dependent WIMP
interactions on F using the superheated droplet technique. A new
generation of detectors and new features which enable background discrimination
via the rejection of non-particle induced events are described. First results
are presented for a subset of two detectors with target masses of F of
65 g and 69 g respectively and a total exposure of 13.75 0.48 kgd. No
dark matter signal was found and for WIMP masses around 24 GeV/c new limits
have been obtained on the spin-dependent cross section on F of
= 13.9 pb (90% C.L.) which can be converted into cross section
limits on protons and neutrons of = 0.16 pb and = 2.60 pb
respectively (90% C.L). The obtained limits on protons restrict recent
interpretations of the DAMA/LIBRA annual modulations in terms of spin-dependent
interactions.Comment: Revised version, accepted for publication in Phys. Lett. B, 20 pages,
7 figure
Theoretical Directional and Modulated Rates for Direct SUSY Dark Matter Detection
Exotic dark matter together with the vacuum energy (cosmological constant)
seem to dominate in the flat Universe. Thus direct dark matter detection is
central to particle physics and cosmology. Supersymmetry provides a natural
dark matter candidate, the lightest supersymmetric particle (LSP). Furthermore
from the knowledge of the density and velocity distribution of the LSP, the
quark substructure of the nucleon and the nuclear structure (form factor and/or
spin response function), one is able to evaluate the event rate for LSP-nucleus
elastic scattering. The thus obtained event rates are, however, very low. So it
is imperative to exploit the two signatures of the reaction, namely the
modulation effect, i.e. the dependence of the event rate on the Earth's motion,
and the directional asymmetry, i.e. the dependence of the rate on the the
relative angle between the direction of the recoiling nucleus and the sun's
velocity. These two signatures are studied in this paper employing various
velocity distributions and a supersymmetric model with universal boundary
conditions at large tan(beta).Comment: 11 LATEX pages, 1 table and 4 ps figures included. Paper presented in
DARK2002, Fourth Heidelberg International Conference on Dark Matter in Astro-
and Particle Physics, Cape Town, South Africa, 4-9 February, 2002, to appear
in the proceedings (to be published by Springer Verlag