9,511 research outputs found
Formalism and quality of a proper motion link with extragalactic objects for astrometric satellite missions
The accuracy of the link of the proper motion system of astrometric satellite
missions like AMEX and GAIA is discussed. Monte-Carlo methods were used to
simulate catalogues of positions and proper motions of quasars and galaxies to
test the link. The main conclusion is, that future satellite missions like GAIA
may be ``self-calibrated'' by their measurements of QSOs, while additional
measurements from radio stars or HST-data are needed to calibrate the less deep
reaching astrometric satellite missions of AMEX type.Comment: Accepted for publication in A&A, LaTeX A&A style, 7 pages, 4 figure
Single-spin asymmetries in the leptoproduction of transversely polarized hyperons
We analyze single-spin asymmetries (SSAs) in the leptoproduction of
transversely polarized hyperons within the collinear twist-3
formalism. We calculate both the distribution and fragmentation terms in two
different gauges (lightcone and Feynman) and show that the results are
identical. This is the first time that the fragmentation piece has been
analyzed for transversely polarized hadron production within the collinear
twist-3 framework. In lightcone gauge we use the same techniques that were
employed in computing the analogous piece in , which
has become an important part to that reaction. With this in mind, we also
verify the gauge invariance of the formulas for the transverse SSA in the
leptoproduction of pions.Comment: 12 pages, 1 figure, reference added, version to appear in Phys. Lett.
Dispersion relation formalism for virtual Compton scattering off the proton
We present in detail a dispersion relation formalism for virtual Compton
scattering (VCS) off the proton from threshold into the
-resonance region. Such a formalism can be used as a tool to
extract the generalized polarizabilities of the proton from both unpolarized
and polarized VCS observables over a larger energy range. We present
calculations for existing and forthcoming VCS experiments and demonstrate that
the VCS observables in the energy region between pion production threshold and
the -resonance show an enhanced sensitivity to the generalized
polarizabilities.Comment: 51 pages, 15 figure
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