A Fundamental Test of the Nature of Dark Matter

Dark matter may consist of weakly interacting elementary particles or ofmacroscopic compact objects. We show that the statistics of the gravitationallensing of high redshift supernovae strongly discriminate between these twoclasses of dark matter candidates. We develop a method of calculating themagnification distribution of supernovae, which can be interpreted in terms ofthe properties of the lensing objects. With simulated data we show that >~ 50well measured type Ia supernovae (\Delta m ~ 0.2 mag) at redshifts ~1 canclearly distinguish macroscopic from microscopic dark matter if $\Omega_o\simgt 0.2$ and all dark matter is in one form or the other.Comment: 8 pages, 2 figures, AASTeX, replaced to conform to the version to be published in ApJL. It is now more clearly written and addresses some possible systematic uncertaintie