Abstract
We use a characterization of the fractional Laplacian as a Dirichlet to Neumann operator for an appropriate differential equation to study its obstacle problem. We write an equivalent characterization as a thin obstacle problem. In this way we are able to apply local type arguments to obtain sharp regularity estimates for the solution and study the regularity of the free boundary.
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Caffarelli, L., Salsa, S. & Silvestre, L. Regularity estimates for the solution and the free boundary of the obstacle problem for the fractional Laplacian . Invent. math. 171, 425–461 (2008). https://doi.org/10.1007/s00222-007-0086-6
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DOI: https://doi.org/10.1007/s00222-007-0086-6