Second-order estimates for degenerate complex $k$-Hessian and Christoffel-Minkowski equations

TL;DR

This paper establishes new regularity results for complex $k$-Hessian and Christoffel-Minkowski equations under sharper degenerate conditions, extending known regularity bounds for these nonlinear PDEs.

Contribution

It introduces a novel approach to prove almost $C^{1,1}$ regularity for the complex $k$-Hessian equation and $C^{1,1}$ regularity for the Christoffel-Minkowski equation under a stronger degenerate condition on $f$.

Findings

Almost $C^{1,1}$ regularity for $k extgreater=5$

$C^{1,1}$ regularity for Christoffel-Minkowski equation

Deep exploitation of concavity properties of operators

Abstract

It is known that the complex $k$-Hessian equation admits almost $C^{1,1}$ regularity (i.e., $\sup\Delta u<\infty$) and the Christoffel-Minkowski equation admits $C^{1,1}$ regularity under the sharp degenerate condition $f^{1/(k-1)}\in C^{1,1}$ for a nonnegative right-hand side $f$. Assuming instead the alternative sharp degenerate condition $f^{3/(2k-2)}\in C^{2,1}$, we prove almost $C^{1,1}$ regularity for the complex $k$-Hessian equation when $k\geq5$ and $C^{1,1}$ regularity for the Christoffel-Minkowski equation. The argument deeply exploits various concavity properties of the operators under the stronger regularity assumption on $f$.