Tricritical points in biaxial liquid crystal phases

We further pursue the analysis of a mean-field model recently proposed by Sonnet [Phys. Rev. E 67, 061701 (2003)] to describe nematic biaxial phases. This model, which is based on a simplified version of Straley's pair potential, is characterized by the prediction of a tricritical point along the transition line between uniaxial and biaxial phases. We show that the same model predicts another tricritical point, but along the line of the direct isotropic-to-biaxial transition. Our prediction is quantitative, as it stems from an analytical criterion for tricriticality.