The Casimir effect and mass renormalization for a massive Bosonic string   in background B-field
  We study the Casimir effect for a massive bosonic string terminating on D-brains, and living in a flat space with an antisymmetric background B-field. We find the Casimir energy and Casimir force as functions of the mass and length of the string and show the force does not depend on B-field. We also find the divergent part of the vacuum state energy, as a function of the mass and length of the string and offer an idea for renormalization of the mass of the string. 
Y. Koohsarian and A. Shirzad
hep-th