A Way Out of the Disc Angular Momentum Catastrophe in Hirarchical   Hydrodynamical Simulations
  We present results that suggest that disc angular momentum catastrophes (DAMCs) plaguing hierarchical hydrodynamical simulations of galaxy formation, not including star formation processes, are due to the inward gas transport that follows bar disk instabilities triggered by interactions and mergers. They also show that DAMCs can be easily avoided by including star-forming processes, as they lead unavoidably to the formation of compact stellar bulges that stabilize disks against bars. The formation of disks similar to those observed demands, in addition, that not all the gas is depleted into stars at high z, so that they can be formed at lower z. 
R. Dominguez-Tenreiro, P.B. Tissera, A. Saiz