Lattice QCD calculation of pion electromagnetic mass splitting yields 4.56(22) MeV using Pauli-Villars photon propagator on CLS ensembles, agreeing with experiment after continuum, volume, and physical-point extrapolations.
The Physics of Hadronic Tau Decays
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abstract
Hadronic tau decays represent a clean laboratory for the precise study of quantum chromodynamics (QCD). Observables (sum rules) based on the spectral functions of hadronic tau decays can be related to QCD quark-level calculations to determine fundamental quantities like the strong coupling constant, parameters of the chiral Lagrangian, |V_us|, the mass of the strange quark, and to simultaneously test the concept of quark-hadron duality. Using the best available measurements and a revisited analysis of the theoretical framework, the value alpha_s(m_tau) = 0.345 +- 0.004[exp] +- 0.009[theo] is obtained. Taken together with the determination of alpha_s(m_Z) from the global electroweak fit, this result leads to the most accurate test of asymptotic freedom: the value of the logarithmic slope of 1/alpha_s(s) is found to agree with QCD at a precision of 4%. In another approach, the tau spectral functions can be used to determine hadronic quantities that, due to the nonperturbative nature of long-distance QCD, cannot be computed from first principles. An example for this is the contribution from hadronic vacuum polarization to loop-dominated processes like the anomalous magnetic moment of the muon. This article reviews the measurements of nonstrange and strange tau spectral functions and their phenomenological applications.
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Sequence transformations applied to the fixed-order QCD series for hadronic tau decays produce estimates c5,1 = 298 ± 15, c6,1 = 3431 ± 256, c7,1 = 2.29 ± 0.29 × 10^4 and a predicted δ^(0)_FOPT = 0.2119 ± 0.0040.
The updated SM prediction for the muon anomalous magnetic moment is 116592033(62)×10^{-11}, showing no tension with the experimental average of 38(63)×10^{-11}.
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Electromagnetic pion mass splitting using a Pauli-Villars-regulated photon propagator
Lattice QCD calculation of pion electromagnetic mass splitting yields 4.56(22) MeV using Pauli-Villars photon propagator on CLS ensembles, agreeing with experiment after continuum, volume, and physical-point extrapolations.
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Hadronic tau decays at higher orders in QCD
Sequence transformations applied to the fixed-order QCD series for hadronic tau decays produce estimates c5,1 = 298 ± 15, c6,1 = 3431 ± 256, c7,1 = 2.29 ± 0.29 × 10^4 and a predicted δ^(0)_FOPT = 0.2119 ± 0.0040.
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The anomalous magnetic moment of the muon in the Standard Model: an update
The updated SM prediction for the muon anomalous magnetic moment is 116592033(62)×10^{-11}, showing no tension with the experimental average of 38(63)×10^{-11}.