Systematic study of projection biases in weak lensing analysis

We present a systematic study of projection biases in the weak lensing analysis of the first year of data from the Dark Energy Survey (DES) experiment. In the analysis, we used a Lambda CDM model and three two-point correlation functions. We show that these biases are a consequence of projecting, or marginalizing, over parameters like h, Omega(b), n(s), and Omega(nu)h(2) that are both poorly constrained and correlated with the parameters of interest like Omega(m), sigma(8), and S-8. Covering the relevant parameter space, we show that the projection biases are a function of where the true values of the poorly constrained parameters lie with respect to the parameter priors. For example, biases in the position of the posteriors can exceed the 1.5 sigma level if the true values of h and n(s) are close to the top of the prior's range, and the true values of Omega(b) and Omega(nu)h(2) are close to the bottom of the range of their priors. We also show that in some cases the 1D credible intervals can be overspecified by as much as 30% and coverage can be as low as 27%. Finally, we estimate these projection biases for the analysis of three and six years worth of DES data.