The effect of low mass substructures on the Cusp lensing relation
  It has been argued that the flux anomalies detected in gravitationally lensed QSOs are evidence for substructures in the foreground lensing haloes. In this paper we investigate this issue in greater detail focusing on the Cusp relation which corresponds to images of a source located to the cusp of the inner caustic curve. We use numerical simulations combined with a Monte Carlo approach to study the effects of the expected power law distribution of substructures within LCDM haloes on the multiple images.   Generally, the high number of anomalous flux ratios in the cusp configurations is unlikely explained by 'simple' perturbers (subhaloes) inside the lensing galaxy, either modeled by point masses or extended NFW subhaloes. We considered in our analysis a mass range of 10^5-10^7 Msun for the subhaloes. We also demonstrate that including the effects of the surrounding mass distribution, such as other galaxies close to the primary lens, does not change the results. We conclude that triple images of lensed QSOs do not show any direct evidence for dark dwarf galaxies such as cold dark matter substructure. 
Andrea V. Maccio', Marco Miranda (University of Zurich)