Cosmological constraints from the masses and abundances of L* galaxies
  We place limits on the mean density of the universe and the slope of the linear power spectrum around a megaparsec scale by comparing the universal mass function to the observed luminosity function. Numerical simulations suggest that the dark matter halo mass function at small scales depends only on Omega_m(n_eff+3) independent of the overall power spectrum normalization. Matching the halo abundance to the observed luminosity function requires knowing the relation between the virial mass and luminosity (separately for early and late type galaxies) and the fraction of galaxies that reside in larger halos such as groups and clusters, all of which can be extracted from the galaxy-galaxy lensing. We apply the recently derived values from SDSS and find Omega_m(n_eff+3)= (0.15 \pm 0.05)/(1-f_dh), where f_dh accounts for the possibility that some fraction of halos may be dark or without a bright central galaxy. A model with Omega_m=0.25 and primordial n=0.8 or with Omega_m=0.2 and n=1 agrees well with these constraints even in the absence of dark halos, although with the current data somewhat higher values for Omega_m and n are also acceptable. 
Uros Seljak (Princeton University)