Exactly solvable model for tricritical phenomena

An $n$-component continuous-spin model with a tricritical point is solved exactly in the limit $n\to \infty$. Its properties are derived and are compared with the results of experiments and approximate calculations. The model leads to an analytical description of the features of tricritical points and suggests the use of an approximation procedure for discrete spin systems which is a substantial qualitative and quantitative improvement on mean-field theory.