On static and hydrodynamic biaxial nematic liquid crystals

In the first part of this paper, we will consider minimizing configurations of the Oseen-Frank energy functional $E(n,m)$ for a biaxial nematics $(n, m):\Omega\to \mathbb S^2\times \mathbb S^2$with$n\cdot m=0$ in dimension three, and establish that it is smooth off a closed set of $1$-dimension Hausdorff measure zero. In the second part, we will consider a simplified Ericksen-Leslie system for biaxial nematics $(n,m)$ in a two dimensional domain and establish the existence of a unique global weak solution $(u,n,m)$ that is smooth off at most finitely many singular times for any initial and boundary data of finite energy. They extend to biaxial nematics of earlier results corresponding to minimizing uniaxial nematics by Hardt-Kindelerherer-Lin \cite{HKL} and a simplified hydrodynamics of uniaxial liquid crystal by Lin-Lin-Wang \cite{LLW10} respectively.