Defects, Decay, and Dissipated States
  The worldsheet renormalization group approach to tachyon condensation in string theory is reviewed. The open string case is summarized with examples, and closed string tachyon condensation on nonsupersymmetric orbifolds is examined in detail. The idea that the renormalization group dissipates the localized states associated to the defect is explored. 
Emil J. Martinec