Tricritical phenomena in constrained systems

Abstract
When constraints are applied to a system that has an ideal second-order phase transition, a tricritical point sometimes appears. The thermodynamic properties near such a point are derived and discussed: tricritical homogeneity is demonstrated and some of the characteristic exponents are derived. Also derived are properties of the first-order transition at H=0, the shape of the wings of the tricritical point, and the critical behaviour at the edges of the wings. The tricritical point is shown to be non-classical.