  We develop an alternative formulation of the theory of solitons, polarons and
multipolarons in quasi-one-dimensional degenerate and non-degenerate conducting
polymers, starting from the continuum Hamiltonian introduced by Brazovskii and
Kirova. Based on a convenient real-space representation of the electron Green
function in one dimension, we present a simple method of calculating the Green
function and the density of states in the presence of a single soliton or
polaron defect, using which we derive exact expressions for the soliton,
polaron and multipolaron excitation energies and the self-consistent gap
functions for an arbitrary value of the electron-phonon coupling constant. We
apply our results to $cis$-polyacetylene.
