Is strong CP invariance due to a massless up quark?
Abstract
A standing mystery in the Standard Model is the unnatural smallness of the strong CP violating phase. A massless up quark has long been proposed as one potential solution. A lattice calculation of the constants of the chiral Lagrangian essential for the determination of the up quark mass, 2 alpha8 - alpha5, is presented. We find 2 alpha8 - alpha5 = 0.29 +/- 0.18, which corresponds to mu / md = 0.410 +/- 0.036. This is the first such calculation using a physical number of dynamical light quarks, Nf = 3.
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