Dark energy constraints from the CTIO lensing survey

We perform a cosmological parameter analysis of the 75 deg(2) CTIO lensing survey in conjunction with cosmic microwave background (CMB) and Type Ia supernovae data. For Lambda CDM cosmologies, we find that the amplitude of the power spectrum at low redshift is given by sigma(8) =0.81(-0.15)(+0.15) (95% confidence level), where the error bound includes both statistical and systematic errors. The total of all systematic errors is smaller than the statistical errors, but they do make up a significant fraction of the error budget. We find that weak lensing improves the constraints on dark energy as well. The (constant) dark energy equation of state parameter, w, is measured to be -0.89(-0.21)(+0.16) (95% c. l.). Marginalizing over a constant w slightly changes the estimate of sigma(8) to 0.79(-0.14)(+0.17) (95% c. l.). We also investigate variable w cosmologies but find that the constraints weaken considerably; next-generation surveys are needed to obtain meaningful constraints on the possible time evolution of dark energy.