Isospin breaking in ρππ couplings: ρ+,0 width difference and muon g−2
Abstract
The dominant contribution to the hadronic vaccum polarization (HVP) of the muon g−2 can be calculated using the hadronic spectrum in τ- → π-π0ντ decay, provided isospin breaking (IB) corrections are properly accounted for. Among these corrections, IB in the ρππ coupling has been pointed out as a missing ingredient. In this work, we calculate this IB effect within the impulse approximation using a symmetry-preserving framework based on Dyson-Schwinger and Bethe-Salpeter equations, incorporating fully dressed quark propagators and meson Bethe-Salpeter amplitudes. We then estimate its effect in the HVP contribution to the muon g−2. As a natural extension, we also compute the IB in the ratio of ϕK+K-/ϕK0K0̅ couplings and compare with existing data. We obtain a coupling ratio gρ0π+π-/gρ+π+π0 = 1.0024(17)(1), which yields an isospin-breaking correction of ΔaμHVP,LO[ρππ] = −2.32(1.64)× 10−10 to the two-pion contribution to the muon anomalous magnetic moment extracted from τ decay data.
Related
- Electromagnetic isospin breaking in hadronic vacuum polarization within a VMD model
- Influence of configuration-interaction on isospin impurities and isospin symmetry breaking corrections to superallowed 0+→ 0+ beta decays
- The hadronic-vacuum-polarization contribution to the muon anomalous magnetic moment in isospin-symmetric lattice QCD with twisted-mass fermions
- Testing strong isospin breaking effects in QCD thermodynamics
- Isospin and flavor SU(3) symmetry breaking in doubly heavy baryons
BibTeX
@misc{bashir2026isospin,
title = {{Isospin breaking in $ρππ$ couplings: $ρ^+,0$ width difference and muon $g-2$}},
author = {A. Bashir and G. López-Castro and K. Raya},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.28506},
eprint = {2610.28506},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.28506},
}
RIS
TY - UNPB
TI - Isospin breaking in ρππ couplings: ρ^+,0 width difference and muon g−2
AU - A. Bashir
AU - G. López-Castro
AU - K. Raya
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.28506
UR - https://arxiv.org/abs/2610.28506
AB - The dominant contribution to the hadronic vaccum polarization (HVP) of the muon g−2 can be calculated using the hadronic spectrum in τ^- → π^-π^0ν_τ decay, provided isospin breaking (IB) corrections are properly accounted for. Among these corrections, IB in the ρππ coupling has been pointed out as a missing ingredient. In this work, we calculate this IB effect within the impulse approximation using a symmetry-preserving framework based on Dyson-Schwinger and Bethe-Salpeter equations, incorporating fully dressed quark propagators and meson Bethe-Salpeter amplitudes. We then estimate its effect in the HVP contribution to the muon g−2. As a natural extension, we also compute the IB in the ratio of ϕK^+K^-/ϕK^0K^0̅ couplings and compare with existing data. We obtain a coupling ratio g_ρ^0π^+π^-/g_ρ^+π^+π^0 = 1.0024(17)(1), which yields an isospin-breaking correction of Δa_μ^HVP,LO[ρππ] = −2.32(1.64)× 10^−10 to the two-pion contribution to the muon anomalous magnetic moment extracted from τ decay data.
ER -