Closed time-like curves and weak energy condition

We examine in detail the relation between the weak energy condition and the condition for the absence of closed time-like curves. Using a new and other exact solutions we show that, in the absence of torsion, the weak energy condition (with a proper boundary condition) always implies the absence of the closed time-like curves, but the converse does not always hold true. Furthermore we show that when the torsion becomes dynamical, the weak energy condition may have nothing to do with the closed time-like curves. (C) 1997 Published by Elsevier Science B.V.