arXiv subjects
Publications and source records attributed to Giacomo Colombo.
We prove optimal $(n-1)$-semiconvexity estimates for solutions to the classical obstacle problem, possibly with a smooth right-hand side. We deduce that the mean curvature of the free boundary is universally bounded above in all dimensions. Existing examples show that full curvature bounds fail in dimensions three and higher. Noticeably, these results are novel even for a constant right-hand side in the $n=2$ case.
We show that the free boundary of a solution of the Stefan problem in $\mathbb R^{4+1}$ is a $3$-dimensional manifold of class $C^\infty$ in $\mathbb R^4$ for almost every time. This is achieved by showing that for all dimensions $n$ the singular set $\Sigma\subset \mathbb R^{n+1}$ can be decomposed in two parts $\Sigma=\Sigma^\infty\cup \Sigma^*$, where $\Sigma^\infty$ is covered by one $(n-1)$-dimensional manifold of class $C^\infty$ in $\mathbb R^{n+1}$ and its projection onto the time axis has Hausdorff dimension 0, while $\Sigma^*$ is parabolically countably $(n-2)$-rectifiable.
It is a well-known conjecture in $\beta$-models and in their discrete counterpart that, generically, external potentials should be ``off-critical'' (or, equivalently, ``regular''). Exploiting the connection between minimizing measures and thin obstacle problems, we give a positive answer to this conjecture.