Chiral perturbation in dense matter and meson condensation controversy
  An outstanding problem in the study of possible kaon condensation is the striking discrepancy between the results of chiral perturbation theory and those of the PCAC-plus-current-algebra approach. I discuss here what causes this discrepancy and what needs to be done to solve the problem. In addition, I point out the importance of examining the validity of the non-relativistic approximation universally employed in the existing treatments of kaon condensation. 
Kuniharu Kubodera