Improved regularity for a Hessian-dependent functional

Abstract: We prove that minimizers of the $L^{d}$-norm of the Hessian in the unit ball of $\mathbb{R}^d$ are locally of class $C^{1,\alpha}$. Our findings extend previous results on Hessian-dependent functionals to the borderline case and resonate with the H\"older regularity theory available for elliptic equations in double-divergence form.