QCD Strings as Constrained Grassmannian Sigma Model:

We present calculations for the effective action of string world sheet in R 3 and R 4 utilizing its correspondence with the constrained Grassmannian σ -model. Minimal surfaces describe the dynamics of open strings while harmonic surfaces describe that of closed strings. The one-loop effective action for these are calculated with instanton and anti-instanton background, representing N-string interactions at the tree level. The effective action is found to be the partition function of a classical modified Coulomb gas in the confining phase, with a dynamically generated mass gap.