The Pseudoscalar Meson Mass to Two Loops in Three-Flavor Partially   Quenched $\chi$PT
  This paper presents a first study of the pseudoscalar meson masses to two loops, or NNLO, within the supersymmetric formulation of partially quenched chiral perturbation theory (PQ$\chi$PT). The expression for the pseudoscalar meson mass in the case of three valence and three sea quarks with equal masses, but different from each other, is given to ${\cal O}(p^6)$, along with a numerical analysis. 
Johan Bijnens, Niclas Danielsson and Timo A. Lahde (Lund)