On the Jeans Instability During the QCD Phase Transition
  The Jeans scale is estimated during the coexistence epoch of quark-gluon and hadron phases in the first-order QCD phase transition. It is shown that, contrary to the previous claims, reduction of the sound speed is so little that the phase transition does not affect evolution of cosmological density fluctuations appreciably. 
Michiyasu Nagasawa and Jun'ichi Yokoyama (YITP, Kyoto University)