Staggered chiral perturbation theory in the two-flavor case and SU(2) analysis of the MILC data

In the light pseudoscalar sector, we study rooted staggered chiral perturbation theory in the two-flavor case. The pion mass and decay constant are calcula ted through NLO for a partiallyquenched theory. In the limit where the strange quark mass is large compared to the light quark masses and the taste splittings, we show that the SU(2) staggered chiral theory emerges from the SU(3) staggered chiral theory, as expected. Explicit relat ions between SU(2) and SU(3) low energy constants and taste-violating parameters are given. A brief summary of updated SU(2) chiral fits to the MILC lattice data is presented.