BPS Domain Walls in Massive Hyper-Kahler Sigma Models
  We discuss hypermultiplets admitting degenerate discrete vacua and BPS domain walls interpolating them. This talk is based on the original papers, hep-th/0307274, hep-th/0211103 and hep-th/0302028. 
Masato Arai, Muneto Nitta and Norisuke Sakai