Probing the Structure of Dark Matter in Galaxy Halos and Clusters using   Supernovae
  A new method for measuring gravitational lensing with high redshift type Ia supernovae is investigated. The method utilizes correlations between foreground galaxies and supernova brightnesses to substantially reduce possible systematic errors and increase the signal to noise ratio. It is shown that this lensing signal can be related to the mass, size and substructure of galaxy halos and galaxy clusters if dark matter consists of microscopic particles. This technique may be particularly useful for measuring the size of dark matter halos, a measurement to which the lensing of galaxies is not well suited, and for measuring the level of substructure in galaxy halos, a problematic prediction of the cold dark matter model. The contributions to the signal from galaxy halos and galaxy clusters are modeled and contributions to the noise from fluctuations in the galaxy number counts, galaxy redshift error, dispersion in SN luminosities and sample variance are estimated. The intrinsic distribution of supernova luminosities and its redshift evolution are removed as major sources of uncertainty. The method is found to be complimentary to galaxy--galaxy lensing. The required observations of $\simgt 100$ supernovae have already been proposed for the purposes of cosmological parameter estimation. 
R. Benton Metcalf (IoA, Cambridge)