  The phase spaces of the two- and three-frequency sine-Gordon models are
examined in the framework of truncated conformal space approach. The focus is
mainly on a tricritical point in the phase space of the three-frequency model.
We give substantial evidence that this point exists. We also find the critical
line in the phase space and present TCSA data showing the change of the
spectrum on the critical line as the tricritical endpoint is approached. We
find a few points of the line of first order transition as well.

High Energy Physics - Theory;Other Condensed Matter