Relativistically Invariant Description of Fluctuations Against the   Background of Classical Kink Solutions
  A relativistically invariant scheme for the description of excited states in a one-kink sector is formulated. The normal oscillations of fluctuations against the background of a moving kink are determined. Zero mode of these oscillations is excluded automatically due to the properties of the integral equation describing normal oscillations. A Hamiltonian for elementary excitations is obtained reflecting the relativistic nature of the problem considered. (35 kb) 
V. D. Tsukanov