  A mixed graph is obtained by orienting some edges of a simple graph. The
positive inertia index of a mixed graph is defined as the number of positive
eigenvalues of its Hermitian adjacency matrix, including multiplicities. This
matrix was introduced by Liu and Li, independently by Guo and Mohar, in the
study of graph energy. Recently, Yuan et al. characterized the mixed graphs
with exactly one positive eigenvalue. In this paper, we study the positive
inertia indices of mixed graphs and characterize the mixed graphs with cut
vertices having positive inertia index 2.
