Validity of ChPT -- is M_\pi=135 MeV small enough ?

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I discuss the practical convergence of the SU(2) ChPT series in the meson sector, based on 2+1 flavor lattice data by the Wuppertal-Budapest and Budapest-Marseille-Wuppertal collaborations.

• These studies employ staggered and clover-improved Wilson fermions, respectively.
• In both cases large box volumes and several lattice spacings are used, and the pion masses reach down to the physical mass point.
• We conclude that LO and NLO low-energy constants can be determined with controlled systematics, if there is sufficient data between the physical mass point and about 350 MeV pion mass.