4,432 research outputs found
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]
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