Szabolcs Borsanyi, Stephan Durr, Zoltan Fodor, Stefan Krieg, Andreas Schafer, Enno E Scholz, Kalman K Szabo
We extract the NLO low-energy constants \bar\ell_3 and \bar\ell_4 of SU(2) chiral perturbation theory, based on precise lattice data for the pion mass and decay constant on ensembles generated by the Wuppertal-Budapest collaboration for QCD thermodynamics. These ensembles feature 2+1 flavors of 2-fold stout-smeared dynamical staggered fermions combined with Symanzik glue, with pion masses varying from 135 MeV to 435 MeV, lattice scales between 0.7 GeV and 2.0 GeV, while m_s is kept fixed at its physical value. Moderate taste splittings and the scale being set through the pion decay constant allow us to restrict ourselves to the taste pseudoscalar state and to use formulae from continuum ChPT. Finally, by dropping the data points near 135 MeV from the fits, we can explore the range of pion masses that is needed in SU(2) ChPT to reliably extrapolate to the physical point.
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http://arxiv.org/abs/1205.0788
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