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A goal of forthcoming imaging surveys is to use weak gravitational lensingshear measurements to constrain dark energy. We quantify the importance ofuncalibrated photometric redshift outliers to the dark energy goals offorthcoming imaging surveys in a manner that does not assume any particularphotometric redshift technique or template. In so doing, we provide anapproximate blueprint for computing the influence of specific outlierpopulations on dark energy constraints. We find that outliers whose photo-zdistributions are tightly localized about a significantly biased redshift mustbe controlled to a per-galaxy rate of <~ a few times 10^-3 to insure thatsystematic errors on dark energy parameters are rendered negligible. In thecomplementary limit, a subset of imaged galaxies with uncalibrated photometricredshifts distributed over a broad range must be limited to fewer than aper-galaxy error rate of <~ a few times 10^-4. Additionally, we explore therelative importance of calibrating the photo-z's of a core set of relativelywell-understood galaxies as compared to the need to identify potentialcatastrophic photo-z outliers. We discuss the degradation of the statisticalconstraints on dark energy parameters induced by excising source galaxies athigh- and low-photometric redshifts, concluding that removing galaxies withz_phot >~ 2.4 and z_phot <~ 0.3 may mitigate damaging catastrophic redshiftoutliers at a relatively small (~ 20%) cost in statistical error. In anappendix, we show that forecasts for the degradation in dark energy parameterconstraints due to uncertain photometric redshifts depend sensitively on thetreatment of the nonlinear matter power spectrum. Previous work using PD96 mayhave overestimated the photo-z calibration requirements of future surveys.

A General Study of the Influence of Catastrophic Photometric Redshift Errors on Cosmology with Cosmic Shear Tomography