Constrain on possible pairing symmetry in a two-orbital model of   FeAs-based superconductors
  In this work, we establish a few exact identities through commutation of intra-orbital and inter-orbital on-site pairings with a two-orbital model describing newly discovered FeAs-based superconductors. Applying the conclusion drawn from rigorous relation and physical interpretation, we give constraints on the possible symmetries of the superconducting pairing of the model. Hence the favorable pairings in newly discovered high-temperature oxypnictide superconductors are proposed. 
Wen-Long You, Shi-Jian Gu, Guang-Shan Tian, and Hai-Qing Lin