Developments in field theory

We develop techniques for computing S-matrix elements for non-polynomial Lagrangians with derivative interactions. The problem of ambiguity present in such an approach is discussed. The ultra-violet properties of the amplitudes are considered in configuration and momentum spaces. A self-consistent approach is suggested for dealing with the Chiral Lagrangians. The above techniques are then applied to compute the pion mass and ππ scattering lengths. The problem of equivalence of S-matrix elements for Chiral Lagrangians related to one another by non-linear field transformations is discussed. Finally the techniques are applied to discuss the renormalizability of neutral massive spin one theory with pseudo-vector coupling to nucleons.