Weak Weak Lensing : How Accurately Can Small Shears be Measured?

Abstract: Now that weak lensing signals on the order of a percent are actively being searched for (cosmic shear, galaxy-galaxy lensing, large radii in clusters...) it is important to investigate how accurately weak shears can be determined. Many systematic effects are present, and need to be understood. I show that the Kaiser et al. technique can leave residual systematic errors at the percent level (through imperfect PSF anisotropy correction), and present an alternative technique which is able to recover shears a factor of ten weaker.