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Isospin breaking corrections in 2π production in tau decays and e^+e^- annihilation: consequences for the muon g-2 and CVC tests

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arxiv 2411.07696 v3 pith:ZJ4YRK2V submitted 2024-11-12 hep-ph hep-exhep-lat

Isospin breaking corrections in 2π production in tau decays and e^+e^- annihilation: consequences for the muon g-2 and CVC tests

classification hep-ph hep-exhep-lat
keywords muoncontributionhadronicresultscorrectionsisospin-breakingpolarizationprediction
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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We revisit the isospin-breaking corrections relating the $e^+e^-$ hadronic cross-section and the tau decay spectral function, focusing on the di-pion channel, that gives the dominant contribution to the hadronic vacuum polarization piece of the muon $g-2$. We test different types of electromagnetic and weak form factors and show that both, the Gounaris-Sakurai and a dispersive-based approach, describe accurately $\tau$ lepton and $e^+e^-$ data (less when KLOE measurements are included in the fits) and comply reasonably well with analyticity constraints. From these results we obtain the isospin-breaking contribution to the conserved vector current (CVC) prediction of the ${\rm BR}(\tau \to \pi\pi\nu_{\tau})$ and to the $2\pi$ hadronic vacuum polarization (HVP) contribution to the muon $g-2$, in agreement with previous determinations and with similar precision. Our results abound in the convenience of using tau data-based results in the updated data-driven prediction of the muon $g-2$ in the Standard Model.

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Cited by 9 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Electroweak precision physics via angular distributions in hadronic $\tau$ decays

    hep-ph 2026-06 accept novelty 7.0

    Angular moments in two-pseudoscalar tau decays give form-factor-independent SM relations that tensor new physics and scalar mass effects can break.

  2. Pion $\beta$ decay and $\tau\to\pi\pi\nu_\tau$ beyond leading logarithms

    hep-ph 2026-02 conditional novelty 7.0

    Pion β decay and τ→ππν short-distance radiative corrections are matched at NLL accuracy with evanescent-scheme dependence cancelled, giving Δ_RC^{πℓ}=0.03403(11) and a τ-HVP isospin-breaking shift of −0.07(4)×10^-10.

  3. Radiative return at NLOPS accuracy

    hep-ph 2026-01 conditional novelty 7.0

    First implementation of NLO corrections matched to a parton shower for the radiative processes e+e−→π+π−γ and e+e−→μ+μ−γ, including ISR, FSR and their interference.

  4. Isospin-breaking effects in inclusive hadronic $\tau$ data for the muon $(g-2)$ from first principles

    hep-lat 2026-07 unverdicted novelty 6.0

    A lattice QCD+QED strategy is outlined for calculating isospin-breaking effects in inclusive tau decays to support high-precision HVP contributions to muon g-2.

  5. Electroweak precision physics via angular distributions in hadronic $\tau$ decays

    hep-ph 2026-06 unverdicted novelty 6.0

    Angular information in hadronic tau decays enables form-factor-independent electroweak observables with first-principles SM predictions and BSM sensitivity.

  6. Comparison of the hadronic vacuum polarization between hadronic $\tau$-decay data and lattice QCD

    hep-ph 2026-05 conditional novelty 6.0

    Isospin-corrected inclusive τ spectral functions yield light-quark-connected HVP and window quantities consistent with lattice QCD, but the 2π⁻π⁺π⁰ mode differs significantly from e⁺e⁻-based Pais expectations.

  7. Revisit of the electromagnetic correction to $\tau\to\pi\pi\nu_\tau$ and its implication for muon $g-2$ based on $\tau$ data

    hep-ph 2025-10 conditional novelty 5.0

    Including scalar contributions to the omega->pi0 pi0 gamma fit revises G_EM(t); with the new correction, tau data give a_mu^HVP,LO(pi pi) = 516.0e-10 and a 2.7 sigma muon g-2 discrepancy.

  8. The anomalous magnetic moment of the muon in the Standard Model: an update

    hep-ph 2025-05 accept novelty 5.0

    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}.

  9. Comparison of the hadronic vacuum polarization between hadronic $\tau$-decay data and lattice QCD

    hep-ph 2026-05 unverdicted novelty 4.0

    Lattice QCD and tau-decay dispersive calculations of isospin-one HVP generally agree, except for a significant difference in the 2π−π+π0 four-pion mode contribution to window quantities.