Pogorelov interior estimates for general sum-type Hessian equations

In this paper, we exploit the concavity of sums of Hessian operators to derive Pogorelov estimates for corresponding equations under the dynamic semi-convexity assumption, and we further obtain several Liouville-type results. Moreover, when k=n-1 and k=n we establish Pogorelov estimates in the admissible cone. As an application, we prove that any entire admissible solution in ${\mathbb{R}}^n$ with quadratic growth must be a quadratic polynomial.