Pairing Symmetry in a Two-Orbital Exchange Coupling Model of Oxypnictides

We study the pairing symmetry of a two-orbital J(1)-J(2) model for FeAs layers in oxypnictides. We show that the mixture of an intraorbital unconventional s(x)(2)y(2)similar to cos(k(x))cos(k(y)) pairing symmetry, which changes sign between the electron and hole Fermi surfaces, and a very small d(x)(2)-y(2)similar to cos(k(x))-cos(k(y)) component is favored in a large part of the J(1)-J(2) phase diagram. A pure s(x)(2)y(2) pairing state is favored for J(2)> J(1). The signs of the d(x)(2)-y(2) order parameters in the two different orbitals are opposite. While a small d(xy)similar to sin(k(x))sin(k(y)) interorbital pairing coexists in the above phases, the intraorbital d(xy) pairing is not favored even for large J(2).