Is the up-quark massless?

Abstract

We report on determinations of the low-energy constants alpha5 and alpha8 in the effective chiral Lagrangian at O(p^4), using lattice simulations with N_f=2 flavours of dynamical quarks. Precise knowledge of these constants is required to test the hypothesis whether or not the up-quark is massless. Our results are obtained by studying the quark mass dependence of suitably defined ratios of pseudoscalar meson masses and matrix elements. Although comparisons with an earlier study in the quenched approximation reveal small qualitative differences in the quark mass behaviour, numerical estimates for alpha5 and alpha8 show only a weak dependence on the number of dynamical quark flavours. Our results disfavour the possibility of a massless up-quark, provided that the quark mass dependence in the physical three-flavour case is not fundamentally different from the two-flavour case studied here.

references added, typos corrected

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Cited by in corpus (20)

• Few-Nucleon Forces and Systems in Chiral Effective Field Theory
• Chiral Perturbation Theory and Baryon Properties
• Twisted-mass lattice QCD with mass non-degenerate quarks
• Partially quenched chiral perturbation theory without ${\Phi }_0$
• Computation of the strong coupling in QCD with two dynamical flavours
• Non-perturbative improvement of the axial current for dynamical Wilson fermions
• Effects of Squark Processes on the Axino CDM Abundance
• Eta decays at and beyond ${\mathbf{p}}^4$ in Chiral Perturbation Theory
• Improved Wilson QCD simulations with light quark masses
• Strong-weak CP hierarchy from non-renormalization theorems
• Chiral Effective Lagrangian and Quark Masses
• Wilson fermions with chirally twisted mass
• Partially quenched chiral perturbation theory and numerical simulations
• Quark mass dependence of pseudoscalar masses and decay constants on a lattice
• Quark mass dependence of masses and decay constants of the pseudo-Goldstone bosons in QCD
• Chiral perturbation theory for partially quenched twisted mass lattice QCD
• Gauging Away the Strong CP Problem
• Hard hadron spectroscopy
• Hadron spectroscopy of twisted mass lattice QCD at beta = 6.0
• Lattice QCD with light dynamical quarks