Excited States of the Double sine-Gordon Model

Using the Gaussian wave functional as variational ground state, we study the excited states of the double sine-Gordon model in (D+1) dimensions. We find, i) for D < 3 there exist twoparticle bound states, their energy decreases with increasing coupling; ii) also for D < 3, the phase shift of the two-particle scattering state is always positive; iii) for D ≥ 3 the investigation on the interaction between the particles shows that the theory is trivial.