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 alpha_8 - alpha_5, is presented. We find 2 alpha_8 - alpha_5 = 0.29 +/- 0.18, which corresponds to m_u / m_d = 0.410 +/- 0.036. This is the first such calculation using a physical number of dynamical light quarks, N_f = 3.

4 pages, 5 figures, submitted to Phys. Rev. Lett., corrected small normalization error in f_pi (conclusions were unaffected), improved lattice spacing analysis, improved finite volume analysis

References in corpus (1)

• Flavor Symmetry and the Static Potential with Hypercubic Blocking

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