On the nonlinear thin obstacle problem

The thin obstacle problem or $n$-dimensional Signorini problem is a classical variational problem arising in several applications, starting with its first introduction in elasticity theory. The vast literature concerns mostly quadratic energies, whereas only partial results have been proved in the nonlinear case. In this paper we consider the thin boundary obstacle problem for a general class of nonlineraities and we prove the optimal $C^{1,\frac{1}{2}}$-regularity of the solutions in any space dimension.