Is the up quark massless?
نویسندگان
چکیده
منابع مشابه
Is the Up Quark Massless?
The symmetries of QCD allow for a CP breaking term in the QCD Lagrangian. However, measurements of the neutron dipole moment have demonstrated that the coefficient of this term is very small, if not zero. The unnatural smallness of this coefficient is known as the strong CP problem. A massless up quark has long been proposed as a potential elegant solution to the problem. Without the up quark m...
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We report on determinations of the low-energy constants α 5 and α 8 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 pseudosc...
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We introduce a parity RF to introduce naturally small masses for the first family members and in particular almost massless u quark toward the strong CP solution. We also discuss the phenomenological implications of this model on the proton decay and the neutrino mass. Furthermore, it is possible to embed this RF parity to local U(1)R gauge symmetry.
متن کاملPartially Quenched Chiral Perturbation Theory and a Massless Up Quark: A Lattice Calculation of the Light-Quark-Mass Ratio
The nontrivial topological structure of the QCD gauge vacuum generates a CP breaking term in the QCD Lagrangian. However, measurements of the neutron electric dipole moment have demonstrated that the term’s coefficient is unnaturally small, a dilemma known as the strong CP problem. A massless up quark has long been seen as a potential solution, as the term could then be absorbed through the res...
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We present the two-loop helicity amplitudes for the scattering of massless quarks in QCD. We use projector techniques to compute the coefficients of the general four-quark amplitude at up to two-loops in conventional dimensional regularisation and use these coefficients to derive the helicity amplitudes in the ’t Hooft-Veltman scheme. The structure of the infrared divergences agrees with that p...
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ژورنال
عنوان ژورنال: Nuclear Physics B - Proceedings Supplements
سال: 2002
ISSN: 0920-5632
DOI: 10.1016/s0920-5632(01)01669-3