Effect of three-particle correlations in low dimensional Hubbard models

A simple approximation which captures some non-perturbative aspects of the one electron Green function of strongly interacting Fermion systems is developed. It provides a way to go one step beyond the usual dilute limit since particle-particle as well as particle-hole scattering are treated on the same footing. Intermediate states are constrained to contain only one particle-hole excitation besides the incoming particle. The Faddeev equations resulting from an exact treatment of this three-body problem are investigated. In one dimension the method is able to show spin and charge decoupling, but does not reproduce the exact nature of power-law singularities. Hey dudes, check out the analytical solution in section III!Comment: 21 pages plus six figures (appended as postscript files) in RevTeX v.

Planck 2013 results. VI. High Frequency Instrument data processing

We describe the processing of the 531 billion raw data samples from the High Frequency Instrument (HFI), which we performed to produce six temperature maps from the first 473 days of Planck-HFI survey data. These maps provide an accurate rendition of the sky emission at 100, 143, 217, 353, 545, and 857GHz with an angular resolution ranging from 9.\ub47 to 4.\ub46. The detector noise per (effective) beam solid angle is respectively, 10, 6 , 12, and 39 muK in the four lowest HFI frequency channels (100-353GHz) and 13 and 14 kJy sr-1 in the 545 and 857 GHz channels. Relative to the 143 GHz channel, these two high frequency channels are calibrated to within 5% and the 353 GHz channel to the percent level. The 100 and 217 GHz channels, which together with the 143 GHz channel determine the high-multipole part of the CMB power spectrum (50 <l < 2500), are calibrated relative to 143 GHz to better than 0.2%

Planck 2013 results. XX. Cosmology from Sunyaev-Zeldovich cluster counts

We present constraints on cosmological parameters using number counts as a function of redshift for a sub-sample of 189 galaxy clusters from the Planck SZ (PSZ) catalogue. The PSZ is selected through the signature of the Sunyaev-Zeldovich (SZ) effect, and the sub-sample used here has a signal-to-noise threshold of seven, with each object confirmed as a cluster and all but one with a redshift estimate. We discuss the completeness of the sample and our construction of a likelihood analysis. Using a relation between mass M and SZ signal Y calibrated to X-ray measurements, we derive constraints on the power spectrum amplitude sigma8 and matter density parameter Omega_m in a flat Lambda CDM model. We test the robustness of our estimates and find that possible biases in the Y-M relation and the halo mass function are larger than the statistical uncertainties from the cluster sample. Assuming the X-ray determined mass to be biased low relative to the true mass by between zero and 30%, motivated by comparison of the observed mass scaling relations to those from a set of numerical simulations, we find that sigma8 = 0.75 \ub1 0.03, Omega_m = 0.29 \ub1 0.02, and sigma8(Omegam/ 0.27)0.3 = 0.764 \ub1 0.025. The value of sigma8 is degenerate with the mass bias; if the latter is fixed to a value of 20% (the central value from numerical simulations) we find sigma8(Omega_m/0.27)0.3 = 0.78 \ub1 0.01 and a tighter one-dimensional range sigma8 = 0.77 \ub1 0.02. We find that the larger values of sigma8 and Omegam preferred by Planck's measurements of the primary CMB anisotropies can be accommodated by a mass bias of about 40%. Alternatively, consistency with the primary CMB constraints can be achieved by inclusion of processes that suppress power on small scales relative to the LambdaCDM model, such as a component of massive neutrinos. We place our results in the context of other determinations of cosmological parameters, and discuss issues that need to be resolved in order to make further progress in this field