Is the Up Quark Massless?
Several lattice calculations of a combination of the low energy constants of the chiral Lagrangian, 2α_8-α_5, are presented. This combination is critical for the preclusion of a massless up quark. The result found is 2α_8-α_5 = 0.115 \pm 0.051^{stat} \pm 0.25^{syst}, which is well outside of the range allowed by a massless up quark.
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