  We investigate from first principles the introduction of isospin-1 vector and
axial-vector fields into the nonlinear sigma model. Chiral symmetry is
nonlinearly realised and spin-1 fields are assumed to transform homogeneously
under chiral rotations. By requiring the Hamiltonian of the theory to be
bounded from below we find inequalities relating three- and four-point meson
couplings. This leads to a low-energy phenomenological Lagrangian for the
nonanomalous sector of $\pi\rho a_1$ strong interactions.
