The program is concerned with developing and verifying the validity of observational methods for constraining the properties of dark matter and dark energy in the Universe. This is the final of three annual reports on progress achieved. Excellent progress has been made in comparing observational projects involving weak gravitational lensing using both ground and space-based instruments, in further constraining the nature of dark matter via precise measures of its distribution in clusters of

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... xies using strong gravitational lensing, in demonstrating the possible limitations of using distant supernovae in future dark energy missions, and in investigating the requirement for ground-based surveys of baryonic acoustic oscillations. The grant has been used primarily to provide support for a very productive postdoctoral researcher -Dr Richard Massey. A small amount of funding has covered research done under Caltech's summer undergraduate research program (Mikelsons) and a visitor program (High -Harvard; Refregier & Bergé -CEA, Paris; Leauthaud -Marseille; Sullivan -Toronto; Nugent -LBL). Strong collaborative programs have continued with others at JPL (Seiffert, Rhodes), Caltech (Gal-Yam), Arizona (Sand), UC Santa Barbara (Treu), in Japan (Miyazaki, Suto) and the UK (Lahav, Peacock, Smith). Much of the dark energy studies fall under the umbrella collaboration of the SNAP mission (LBL PIs: Levi, Perlmutter) -a strong contender for the DoE/NASA Joint Dark Energy Mission (JDEM). During this 9 month reporting period, 16 refereed papers have appeared or been accepted, a further 4 submitted for publication. 5 further papers are nearing completion. Gravitational Lensing Weak gravitational lensing utilizes the distorted shapes of thousands of faint background galaxies to infer the foreground distribution of dark matter. Slicing the background population via photometric redshifts enables the growth of structure to be measured and this, in turn, represents a powerful measure of the balance between gravity and dark energy. We have made particularly good progress in this area, both technically through comparative tests of simulations, and scientifically in demonstrating the first timedependent dark matter signal with actual faint data. A major thrust is the technical evaluation of the future prospects for weak lensing as a dark energy probe via the analysis of both simulated and real data. Weak lensing can also be used to locate individual dark matter halos and hence to count their distribution in space and time. With the addition of strong lensing constraints, the dark matter distribution