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    Verification and Uncertainty Quantification

The level of accuracy required by dark energy experiments represents a major challenge: Predictions and data analysis methods must match -- and preferably exceed -- the observational accuracy. Achieving this goal requires (i) rigorous code verification, and (ii) advanced methods for estimating cosmological and model parameters using observations and simulations. We have recently carried out a comprehensive code comparison project, finding that statistics such as the matter power spectrum only agree at the ~5-10% level in regimes where much better results were expected. (An extended code comparison project is in progress. More soon!) This is an order of magnitude shy of the required accuracy. A major new effort is required to discover the ultimate error limits.

A key challenge for precision cosmology is the accurate determination of parameters from observations and simulations. Commonly-used fitting functions are too crude for precision work. Direct use of simulations is essential for the physics to be correctly captured. Simulations, however, are very expensive, and only a restricted number can be performed; a billion-particle simulation with HOT takes 2*10^17 flops of computation at a cost of 30K processor-hours. A new methodology to combat this problem has been outlined by us recently and will be a major cornerstone of this project.

Publications
  1. Simulations and cosmological inference: A statistical model for power spectra means and covariances
    M.D. Schneider, L. Knox, S. Habib, K. Heitmann, D. Higdon, C. Nakhleh, Phys. Rev. D submitted, arXiv:0806.1487
  2. Constraining Cosmological Parameters by Combining Simulations and Physical Observations D. Higdon, C. Nakhleh, S. Habib, and K. Heitmann, invited book chapter, Publisher: Wiley, submitted.
  3. Cosmic Calibration: Constraints from the Matter Power Spectrum and the Cosmic Microwave Background,
    S. Habib, K. Heitmann, D. Higdon, C. Nakhleh, and B. Williams, Phys. Rev. D76, 083503 (2007), astro-ph/0702348

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