A Strong-Coupling Analysis of the Lattice $CP^{N-1}$ Models in the   Presence of a $\theta$ Term
  A $\theta$ term, which couples to topological charge, is added to the lattice $CP^{N-1}$ model. The strong-coupling character expansion is developed. The series for the free energy and mass gap are respectively computed to tenth order and fourth order. Several features of the strong-coupling analysis emerge. One is the loss of superconfinement. Another is that in the intermediate coupling constant region, there are indications of a transition to a deconfining phase when $\theta$ is sufficiently large. The transition is like the one which has been observed in Monte Carlo simulations of a similar lattice $CP^{N-1}$ action. 
Jan Plefka and Stuart Samuel (City College of New York)