$H^{1+α}$ estimates for the fully nonlinear parabolic thin obstacle problem

Abstract: We study the regularity of the viscosity solution to the fully nonlinear parabolic thin obstacle problem. In particular, we prove that the solution is local $H^{1+\alpha}$ on each side of the smooth obstacle, for some small $\alpha>0.$ Following the method which was first introduced for the harmonic case by Caffarelli in 1979, we extend the results of Fern\'{a}ndez-Real (2016) who treated the fully nonlinear elliptic case. Our results also extend those of Chatzigeorgiou (2019) in two ways. First, we do not assume solutions nor operators to be symmetric. Second, our estimates are local, in the sense that do not rely on the boundary data.