Dark Energy Survey Year 1 results: Cosmological constraints from cosmic shear

We use 26 10 6 galaxies from the Dark Energy Survey (DES) Year 1 shape catalogs over 1321 deg 2 of the sky to produce the most significant measurement of cosmic shear in a galaxy survey to date. We constrain cosmological parameters in both the flat CDM and the wCDM models, while also varying the neutrino mass density. These results are shown to be robust using two independent shape catalogs, two independent photo-z calibration methods, and two independent analysis pipelines in a blind analysis. We find a 3.5% fractional uncertainty on 8 m =0.3 0.5 0.782 0.027 -0.027 at 68% C.L., which is a factor of 2.