Direct SUSY dark matter detection-Theoretical rates due to the spin

The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate in the flat Universe. Thus the direct dark matter detection, consisting of detecting the recoiling nucleus, is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). The relevant cross sections arise out of two mechanisms: i) The coherent mode, due to the scalar interaction and ii) The spin contribution arising from the axial current. In this paper we will focus on the spin contribution, which is expected to dominate for light targets. For both modes it is possible to obtain detectable rates, but in most models the expected rates are much lower than the present experimental goals. So one should exploit two characteristic signatures of the reaction, namely the modulation effect and, in directional experiments, the correlation of the event rates with the sun's motion. In standard non directional experiments the modulation is small, less than two per cent. In the case of the directional event rates we like to suggest that the experiments exploit two features, of the process, which are essentially independent of the SUSY model employed, namely: 1) The forward-backward asymmetry, with respect to the sun's direction of motion, is very large and 2) The modulation is much larger, especially if the observation is made in a plane perpendicular to the sun's velocity. In this case the difference between maximum and minimum can be larger than 40 per cent and the phase of the Earth at the maximum is direction dependent.Comment: 16 Latex pages, 15 figures, 3 table

Explicit pionic degrees of freedom in deuteron photodisintegration in the Delta-resonance region

Photodisintegration of the deuteron above pi-threshold is studied in a coupled channel approach including N-Delta- and pi-d-channels with pion retardation in potentials and exchange currents.Comment: 5 pages latex including 6 postscript figures, talk at the 15th Int. Conf. on Few-Body Problems in Physics, Groningen, Netherlands, 22-26 July 1997. To be published in Nucl. Phys.

Absorption mechanisms in photon induced two-body knockout

Calculations have been performed for the $^{16}$O($\gamma$,pn) and the $^{16}$O($\gamma$,pp) reaction in the photon-energy range $E_{\gamma}$ = 60-300 MeV. Besides the contribution from the more common photoabsorption on the pionic degrees of freedom, we have investigated the influence of heavier meson exchange ($\rho, \sigma, \omega$) and intermediate $\Delta$ creation with $\pi$ and $\rho$ exchange. Whereas the $\pi$ meson is found to set the main trends, the $\rho$ meson is found not to be discardable in a theoretical description of the ($\gamma$,pn) reaction. The incorporation of an energy dependence and a decay width in the $\Delta$ propagator is observed to be essential in order to arrive at a more realistic description of ($\gamma$,NN) reactions at higher photon energies.Comment: 10 pages, 5 figures in seperate postscript file, Submitted to Phys. Lett. B. - INW9306I

Analysis of Δ+(1232)\Delta^{+}(1232) Isobar Observables, with Improved Quark Distribution Amplitudes

A model distribution amplitude for the $\Delta^{+}(1232)$ isobar is proposed, derived on the basis of the QCD sum-rule calculations of Farrar et al. combined with those of Carlson and Poor. The transition form factor $\gamma p\Delta^{+}$ is calculated modeling the proton by selected distribution amplitudes. Furthermore, predictions are made for some exclusive charmonium decays into $\Delta\bar{\Delta}$. The obtained results are compared with other theoretical models and with the available data.Comment: 15 pages, RUB-TPII-22/92 Preprin