Determination of binding energy in field theory using a basis wave-functional expansion

We present a basis wave-functional expansion technique for evaluating the spectra of Bose field theories. Using this technique we study scalar field theory in 1+1 dimensions with the interaction potentials ${\lambda }_0$ ${\phi }^4$ and :λ(${\phi }^6$-${\phi }^4$):. We confirm with increased accuracy (∼0.1%) that the former has no two-particle bound state, and that the latter theory does possess such a bound state. For the latter potential we also find three-particle and four-particle bound states. We calculate the two-particle binding energy in the latter potential for large values of the coupling constant for which previous results are unavailable.