Accurate calculations of the WIMP halo around the Sun and prospects for its gamma-ray detection

Galactic weakly interacting massive particles (WIMPs) may scatter off solar nuclei to orbits gravitationally bound to the Sun. Once bound, the WIMPs continue to lose energy by repeated scatters in the Sun, eventually leading to complete entrapment in the solar interior. While the density of the bound population is highest at the center of the Sun, the only observable signature of WIMP annihilations inside the Sun is neutrinos. It has been previously suggested that although the density of WIMPs just outside the Sun is lower than deep inside, gamma rays from WIMP annihilation just outside the surface of the Sun, in the so called WIMP halo around the Sun, may be more easily detected. We here revisit this problem using detailed Monte Carlo simulations and detailed composition and structure information about the Sun to estimate the size of the gamma-ray flux. Compared to earlier simpler estimates, we find that the gamma-ray flux from WIMP annihilations in the solar WIMP halo would be negligible; no current or planned detectors would be able to detect this flux.Comment: 18 pages, 7 figures, latex, updated to match published version

Doping dependent quasiparticle band structure in cuprate superconductors

We present an exact diagonalization study of the single particle spectral function in the so-called t-t'-t''-J model in 2D. As a key result, we find that unlike the `pure' t-J model, hole doping leads to a major reconstruction of the quasiparticle band structure near (pi,0): whereas for the undoped system the quasiparticle states near (pi,0) are deep below the top of the band at (pi/2,pi/2), hole doping shifts these states up to E_F, resulting in extended flat band regions close to E_F and around (pi,0). This strong doping-induced deformation can be directly compared to angle resolved photoemission results on Sr_2 Cu Cl_2 O_2, underdoped Bi2212 and optimally doped Bi2212. We propose the interplay of long range hopping and decreasing spin correlations as the mechanism of this deformation.Comment: 4 pages, Revtex, with 4 embedded eps figures. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to [email protected]

Landau mapping and Fermi liquid parameters of the 2D t-J model

We study the momentum distribution function n(k) in the 2D t-J model on small clusters by exact diagonalization. We show that n(k) can be decomposed systematically into two components with Bosonic and Fermionic doping dependence. The Bosonic component originates from the incoherent motion of holes and has no significance for the low energy physics. For the Fermionic component we exlicitely perform the one-to-one Landau mapping between the low lying eigenstates of the t-J model clusters and those of an equivalent system of spin-1/2 quasiparticles. This mapping allows to extract the quasiparticle dispersion, statistics, and Landau parameters. The results show conclusively that the 2D t-J model for small doping is a Fermi liquid with a `small' Fermi surface and a moderately strong attractive interaction between the quasiparticles.Comment: Revtex file, 5 pages with 5 embedded eps-files, hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to: [email protected]

Marker für die Zulassung von Maispopulationssorten

The genetic resource of adapted German maize landraces is threatened to get lost. Unsolved admission standards at the Federal Office for Plant Varieties are a main obstacle for breeders to use such material. Until now each application for admission has been rejected due to missing homogeneity. Therefore, population specific marker alleles should be developed and deposited at the Federal Office for Plant Varieties as further selection criteria. A first step is the development of markers for phenotypic apparent traits. We developed three markers for red and white cob glume color and used them for selection of two maize populations. The next step would be the development of non-genic markers. Although these markers have no phenotypic effects they also do not influence yield or other physiological important traits

Temperature dependent band structure of the Kondo insulator

We present a Qantum Monte Carlo (QMC) study of the temperature dependent dynamics of the Kondo insulator. Working at the so-called symmetrical point allows to perform minus-sign free QMC simulations and thus reach temperatures of less than 1% of the conduction electron bandwidth. Study of the temperature dependence of the single particle Green's function and dynamical spin correlation function shows a surprisingly intricate low temperature band structure and gives evidence for two characteristic temperatures, which we identify with the Kondo and coherence temperature, respectively. In particular, the data show a temperature induced metal-insulator transition at the coherence temperature.Comment: RevTex-file, 4 PRB pages with 4 eps figures. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to: [email protected]