Georgios Sakellaris' research lies in the field of partial differential equations. One direction that he is interested in is boundary value problems for second order elliptic equations with lower order coefficients in Lipschitz domains, in the case that the boundary data is not necessarily continuous. Some instances include the D_2 Dirichlet problem in the case that the data is square integrable on the boundary, and the R_2 Regularity problem when both the data and its tangential derivative are square integrable.
Another direction of research is the construction of Green's function for equations with lower order coefficients, in settings that are subcritical or scale invariant. In this direction, he has been investigating the effect that the lower order coefficients have in obtaining pointwise bounds and weak-type bounds for Green's function, in domains with little or no regularity.
Finally, he has lately been interested in free boundary problems involving the fractional Laplacian.