Improved calculation of radiative corrections to $τ\toππν_τ$ decays
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866918382636367872 |
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| author | Colangelo, Gilberto Cottini, Martina Hoferichter, Martin Holz, Simon |
| author_facet | Colangelo, Gilberto Cottini, Martina Hoferichter, Martin Holz, Simon |
| contents | A reliable calculation of radiative corrections to $τ\toππν_τ$ decays is an important prerequisite for using hadronic $τ$ decays for a data-driven evaluation of the hadronic-vacuum-polarization contribution to the anomalous magnetic moment of the muon, $a_μ^\text{HVP, LO}[ππ,τ]$. In this Letter, we present an improved model-independent analysis of these radiative corrections, including, for the first time, effects beyond point-like pions in the evaluation of the loop diagrams. These structure-dependent corrections, implemented via a dispersive representation of the pion form factor, lead to significant changes compared to previous calculations due to enhancements near the $ρ(770)$ resonance. We also devise strategies for the matching to chiral perturbation theory and a stable implementation of the real corrections down to the two-pion threshold, which shows that some higher-order isospin-breaking corrections need to be kept due to a strong threshold enhancement. Finally, we perform dispersive fits to the currently available $τ\toππν_τ$ spectra and discuss the consequences for isospin-breaking corrections in the evaluation of $a_μ^\text{HVP, LO}[ππ,τ]$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_26871 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Improved calculation of radiative corrections to $τ\toππν_τ$ decays Colangelo, Gilberto Cottini, Martina Hoferichter, Martin Holz, Simon High Energy Physics - Phenomenology High Energy Physics - Experiment High Energy Physics - Lattice Nuclear Theory A reliable calculation of radiative corrections to $τ\toππν_τ$ decays is an important prerequisite for using hadronic $τ$ decays for a data-driven evaluation of the hadronic-vacuum-polarization contribution to the anomalous magnetic moment of the muon, $a_μ^\text{HVP, LO}[ππ,τ]$. In this Letter, we present an improved model-independent analysis of these radiative corrections, including, for the first time, effects beyond point-like pions in the evaluation of the loop diagrams. These structure-dependent corrections, implemented via a dispersive representation of the pion form factor, lead to significant changes compared to previous calculations due to enhancements near the $ρ(770)$ resonance. We also devise strategies for the matching to chiral perturbation theory and a stable implementation of the real corrections down to the two-pion threshold, which shows that some higher-order isospin-breaking corrections need to be kept due to a strong threshold enhancement. Finally, we perform dispersive fits to the currently available $τ\toππν_τ$ spectra and discuss the consequences for isospin-breaking corrections in the evaluation of $a_μ^\text{HVP, LO}[ππ,τ]$. |
| title | Improved calculation of radiative corrections to $τ\toππν_τ$ decays |
| topic | High Energy Physics - Phenomenology High Energy Physics - Experiment High Energy Physics - Lattice Nuclear Theory |
| url | https://arxiv.org/abs/2510.26871 |