Breaking the degeneracy: Optimal use of three-point weak lensing statistics

We study the optimal use of three-point statistics in the analysis of weak lensing by large-scale structure. The three-point statistics have long been advocated as a powerful tool to break measured degeneracies between cosmological parameters. Using ray-tracing simulations. incorporating important survey features such as a realistic depth-dependent redshift distribution, we find that a joint two- and three-point correlation function analysis is a much stronger probe of cosmology than the skewness statistic. We compare different observing strategies, showing that for a limited survey time there is an optimal depth for the measurement of three-point statistics, which balances statistical noise and cosmic variance against signal amplitude. We find that the chosen CFHTIS observing strategy was optimal and forecast that a joint two- and three-point analysis of the completed CFHTLS-Wide will constrain the amplitude of the matter power spectrum sigma(8) to 10% and the matter density parameter Omega(m) to 17%, a factor of 2.5 improvement on the two-point analysis alone. Our error analysis includes all non-Gaussian terms, finding that the coupling between cosmic variance and shot noise is a non-negligible contribution which should be included in any future analytical error calculations. (C) 2009 Elsevier B.V. All rights reserved.