Pith. sign in

REVIEW 2 major objections 3 minor 163 references

Towards testing $(g-2)_\tau$ in $e^+e^-\to\tau^+\tau^-$: radiative corrections and projections for Belle II

T0 review · 2 major / 3 minor · reviewed 2026-08-15 · deepseek-v4-flash

Pith's one-line read Complete one-loop QED corrections for fully polarized e+e− → τ+τ− show that a Belle II polarization upgrade could test the tau anomalous magnetic moment at the 10^-5 level.

desk verdict A solid enabling calculation for the polarized-Belle-II tau g-2 program; trust the amplitude, but ask for a direct quantification of the symmetric-cut assumption before accepting the 10^-5 projection. read the letter →

arxiv 2505.09678 v2 pith:6FNFF7VL submitted 2025-05-14 hep-ph hep-exnucl-th

classification hep-phhep-exnucl-th
keywords tauanomalousmagneticmoment(g-2)_tauBelleIIradiativecorrectionspolarizedelectronbeamasymmetryobservablesboxdiagramsMonteCarlointegrator
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper targets the anomalous magnetic moment of the tau lepton, a_tau, the least-well-measured of the three charged leptons and a sensitive place to look for new physics because its Standard Model value is tiny and reliably known. Measuring it directly is hard because the tau decays too quickly, so the proposed route is to extract a_tau from carefully constructed spin asymmetries in e+e− → τ+τ− with a polarized electron beam, as could be realized at a future Belle II polarization upgrade. The paper establishes that this route is viable at the $10^{-5}$ level: it provides the complete one-loop QED radiative corrections for the fully polarized process, implements them in the McMule Monte-Carlo integrator, and introduces a cut-dependent coefficient C(Θ) that restores cancellation of the dominant backgrounds once realistic Belle II angular cuts are applied. The authors also show that the one-loop box diagrams contribute only at O($m_e^{2}$), roughly $10^{-10}$, so they do not spoil the extraction at the targeted precision.

What carries the argument

The load-bearing object is the cut-dependent coefficient C(Θ) in Eq. (3.28), which replaces the constant π/(2γ_τ) in the asymmetry combination A_T − C(Θ) A_L so that the |F_1|^2 and γ–Υ–Z interference contributions vanish after angular integration over a symmetric range [Θ, π − Θ]. The argument is carried by the spin-projected one-loop QED amplitudes, computed for arbitrary polarizations of electron and tau, and by the McMule implementation with FKS infrared subtraction and next-to-soft stabilization, which supplies the numerical cross sections and asymmetries under Belle II cuts. The symmetry table under t ↔ u is the mechanism that renders the box diagrams negligible for the asymmetries.

What would settle it

Evaluate the observable A_T − C(Θ) A_L in a Monte Carlo or data sample that keeps hard photon emission (E_γ > 50 MeV) and uses the true asymmetric Belle II lab-frame boost, without the soft-photon approximation; if the result deviates from the Re F_2 prediction by substantially more than the claimed O($m_e^{2}$) box contribution (about $10^{-10}$), the symmetry assumption underlying the cancellation fails.

Watch

Extended reading notes

Core claim

The central discovery is that the combination A_T − C(Θ) A_L, built from the transverse and longitudinal asymmetries defined with polarized beams, isolates the real part of the Pauli form factor Re F_2 even in the presence of the angular cuts required by the Belle II detector, provided the cuts are symmetric in the center-of-mass frame. The paper derives the coefficient C(Θ) = (π/2 − Θ + sin Θ cos Θ)/(γ_τ $cos^{2}$ Θ), which reduces to the uncut value π/(2γ_τ) when Θ = 0, from the condition that the unwanted |F_1|^2 and γ–Υ–Z interference terms integrate to zero. With this coefficient the observable regains the expected sign and magnitude (about $10^{-4}$) under Belle II conditions. Box diagrams, whose spin-dependent contributions have the opposite symmetry under t ↔ u, cancel in the asymmetries, leaving only corrections of O($m_e^{2}$) of order $10^{-10}$. The paper also re-derives the polarization analyzer α_h for tau decays to spin-0 and spin-1 hadrons, finding α_h = 1 for spin 0 and ($m_τ^{2}$ − $2m_h^{2}$)/($m_τ^{2}$ + $2m_h^{2}$) for spin 1, and notes the enhanced sensitivity of the longitudinal spin-1 component.

Load-bearing premise

The whole cancellation scheme rests on the assumption that the Belle II angular cuts are symmetric in the center-of-mass frame, which the paper notes holds only approximately for soft photons; hard photons or the asymmetric 7 GeV on 4 GeV beam boost would break that symmetry and reintroduce the dominant background terms.

Editorial extensions

If this is right

  • If the central claim is right, a Belle II polarization upgrade could reach a precision of about 10^-5 on a_tau, which is the level needed to probe realistic beyond-Standard-Model scenarios.
  • The C(Θ) prescription removes the need to model the charge form factor and the γ–Υ–Z interference in the analysis, because those contributions cancel in the asymmetry combination by construction.
  • Because the one-loop box diagrams are suppressed by the electron mass to about 10^-10, the NLO prediction for the Re F_2-sensitive observable does not require exact box-diagram control at the current precision target.
  • For spin-1 tau decay modes such as ρ and a_1, isolating the longitudinal polarization component gives a larger effective polarization analyzer, boosting the statistical power of the asymmetry measurement.
  • The outlined extension to NNLO would require two-loop amplitudes with full polarization, NTS stabilization with polarization support, and improved treatment of tau decays beyond the narrow-width approximation.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the symmetry argument extends to other 2 → 2 lepton pair production processes, the same C(Θ) construction could be used to isolate dipole form factors in, for example, e+e− → μ+μ− with polarized beams, where the lighter mass makes the box suppression even stronger.
  • A direct experimental check would be to repeat the asymmetry measurement in a sample with hard photons (E_γ > 50 MeV); the paper's assumptions predict that the cancellation degrades, so the observed residual would quantify the size of the symmetry-breaking contamination.
  • The O(m_e^2) suppression of box diagrams suggests that at NNLO the dominant new corrections will come from two-loop form factors and radiation, not from higher-box topologies; if that holds, the computational roadmap sketched in the paper is likely sufficient.
  • A combined fit of A_T − C(Θ) A_L along with the normal asymmetry sensitive to Re F_3 would constrain both a_tau and the tau electric dipole moment from the same data set, turning the projected 10^-5 precision into a broader dipole-moment program.
Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

2 major / 3 minor

Summary. This paper presents the complete one-loop QED corrections for the fully polarized e+e- -> tau+tau- process, implemented in the McMule Monte Carlo framework, with analytic expressions in Appendix A. The authors construct transverse and longitudinal asymmetries A_T and A_L from polarized electron beams and introduce a cut-dependent coefficient C(Theta) in the combination A_T - C(Theta) A_L to cancel the dominant |F1|^2 and gamma-Upsilon-Z interference contributions under angular cuts. They evaluate the asymmetries for Belle II kinematics (7/4 GeV asymmetric beams, E_gamma < 50 MeV, 17 deg < theta_lab < 150 deg) and find that the combination restores the expected order of magnitude and sign for the ReF2-sensitive observable. They argue that box diagrams are suppressed by O(m_e^2) and therefore negligible, and they outline steps toward NNLO. They conclude that a precision of 10^-5 for a_tau is achievable with a polarized Belle II upgrade.

Significance. If the results hold, this work provides a crucial theoretical foundation for a future a_tau measurement at Belle II. The analytic one-loop expressions and the McMule implementation are validated against OpenLoops and against the no-cut predictions of Ref. [102], and the data and analysis code are publicly released. The introduction of C(Theta) is a useful new observable for controlling cut effects, and the re-evaluation of the polarization analyzer for spin-1 hadrons clarifies a discrepancy in the literature. However, the 10^-5 projection relies on the assumption that the effective CM angular acceptance is symmetric to a precision that is not quantified in the paper.

major comments (2)
  1. [Sec. 3.4 and Sec. 4.1] The cancellation of the |F1|^2 and gamma-Upsilon-Z contributions in O = A_T - C(Theta) A_L is derived under the assumption of exactly symmetric CM angular cuts, Theta < theta < pi - Theta. The paper states in Sec. 3.4 that this holds 'nearly true for soft photons', but it does not quantify the residual contamination when the effective CM acceptance is asymmetric. The numerical estimate |dO/dTheta| = 0.0009(2) quoted in Sec. 3.4 covers only a symmetric shift of both cut boundaries, not an asymmetry between the lower and upper boundaries. Because the 7 GeV/4 GeV beam boost and the lab-frame placement of the E_gamma < 50 MeV cut induce small asymmetries, a 1 deg asymmetry between the CM boundaries would leave an O(10^-3) to O(10^-2) contribution from |F1|^2 in O, well above the 10^-5 target. The paper should provide a quantitative estimate of this residual, e.g., by running McMule with asymmetric cuts (lower boundary Theta - delta, upper boundary pi - Theta + epsilon), and state the required experimental control of the acceptance asymmetry.
  2. [Table 3 and Sec. 4.2] The verification that A_T - C(Theta) A_L vanishes at tree level (Table 3, 0.0000001(3)) and the box-diagram suppression argument (Table 4) both assume the t<->u symmetry of the integration region. They do not probe the NLO real-emission phase space, in which the tau+ and tau- are not exactly back-to-back. Since the E_gamma < 50 MeV cut is applied in the lab frame of an asymmetric collider, the effective CM cuts for real-emission events are only approximately symmetric. The paper should check, e.g., by binning the NLO contributions in the difference of the two tau polar angles, whether the cancellation and the box suppression persist at the claimed 10^-10 level when realistic soft-photon kinematics and the boost are included.
minor comments (3)
  1. [Sec. 5 title] The title of Sec. 5, 'beyond NLO and NW A', contains a typo; it should be 'NWA'.
  2. [Eq. (4.1)] Please specify whether E_gamma < 50 MeV is defined in the lab frame or the CM frame; the discussion of the symmetry of the angular cuts depends on this choice.
  3. [Figs. 2-9] In the legends of Figs. 2-9, the notation tau +/- is used, while the curves appear to show tau+ and tau- separately at NLO; please clarify the meaning of each entry in the legends.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: C(Theta) is an explicitly constructed cancellation coefficient, and the NLO matrix elements are validated against independent external computations.

full rationale

The central new ingredient, C(Theta), is obtained by imposing the cancellation condition in Eq. (3.27), so the subsequent statement that A_T - C(Theta) A_L cancels the dominant |F1|^2 and gamma-Upsilon-Z contributions is true by explicit construction rather than by hidden reuse of fitted data. Equation (3.28) solves the stated integral equation, and the tree-level check in Table 3 is an algebraic consistency check, not a prediction. The ReF2-sensitive combination in Eqs. (3.21)-(3.22) is likewise defined to isolate ReF2, and the paper does not present this definition as an empirical prediction. The one-loop matrix elements are new analytic results (Appendix A), and the numerical implementation is checked against OpenLoops and earlier independent computations (Section 4), so the McMule self-citations are not load-bearing beyond code provenance. The box-diagram suppression (Table 4) is obtained from the explicit t<->u symmetry of the analytic amplitudes; it may be sensitive to the assumed CM-symmetric soft-photon cuts, but that is a limitation or robustness issue, not circularity. No step reduces by construction to its own input, and no fitted parameter is relabeled as a prediction.

Assumptions & free parameters 0 free parameters · 6 assumptions · 0 invented entities

No free parameters are fitted to data: the numerical inputs are PDG values for alpha, m_e, m_tau and sqrt(s) = M_Upsilon(4S), and the cut-dependent coefficient C(Theta) is derived from a cancellation condition, not tuned to the central result. The load-bearing modeling choices are the NWA, the CM-symmetric soft-photon cut approximation, the heavy-new-physics EFT limit for the form factors, and the assumption on the gamma-Upsilon-Z angular shape.

assumptions (6)
  • domain assumption Narrow-width approximation for tau to h nu decays factorizes production from decay.
    Invoked in Sec. 3.2 to reduce e+e- to tau+tau- to h+ nu h- nu into production times decay; the paper notes in Sec. 5 that beyond-NWA corrections may become important at NNLO.
  • domain assumption Angular cuts are symmetric in the CM frame and only soft photons (E_gamma < 50 MeV) are considered.
    Stated in Secs. 3.4 and 4.1; required for the C(Theta) cancellation and for the box-diagram symmetry argument to hold. Hard photons would break the symmetry.
  • domain assumption BSM contributions to the magnetic and electric dipole form factors are approximately constant at sqrt(s) = M_Upsilon(4S), i.e., the heavy-new-physics limit Lambda^2_BSM >> s.
    Used in Sec. 3.1 to translate an asymmetry measurement into a bound on a_tau^BSM and d_tau^BSM via ReF2(s) approximately ReF2^SM(s) + a^BSM.
  • domain assumption The gamma-Upsilon-Z interference contributions have the same angular distribution as the |F1|^2 term and are removed by the same C(Theta) combination.
    Used in Sec. 3.4 to claim the gamma-Upsilon-Z terms cancel in A_T - C(Theta) A_L; the interference is not computed explicitly.
  • standard math Standard on-shell renormalization and four-dimensional FDH (FDF) regularization are valid up to NLO QED for polarized amplitudes.
    The framework of the calculation in Sec. 2; standard practice in QED, used throughout App. A.
  • domain assumption The tau decay analyzer formula is derived assuming tree-level W exchange and hadronic currents with at most one form factor per vertex.
    Sec. 3.3; the conflicting literature values for alpha_h are resolved within this simplified treatment; QED and electroweak corrections to the decay are not included.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Towards testing $(g-2)_\tau$ in $e^+e^-\to\tau^+\tau^-$: radiative corrections and projections for Belle II." pith.science (2026). https://pith.science/paper/6FNFF7VL

@misc{pith2026250509678,
  author       = {Pith},
  title        = {Pith review of: Towards testing $(g-2)_\tau$ in $e^+e^-\to\tau^+\tau^-$: radiative corrections and projections for Belle II},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/6FNFF7VL}},
  note         = {Machine review of arXiv:2505.09678}
}
abstract

The arguably most promising avenue towards testing physics beyond the Standard Model in the anomalous magnetic moment of the $\tau$ proceeds via suitably constructed asymmetries in $e^+e^-\to\tau^+\tau^-$ in the presence of a polarized electron beam. Such a program, as could be realized at Belle II assuming a polarization upgrade of the SuperKEKB $e^+e^-$ collider, crucially relies on a careful consideration of radiative corrections. In this work, we present the complete one-loop result for the fully polarized $e^+e^-\to\tau^+\tau^-$ process and its implementation in the Monte-Carlo integrator McMule. As an application, we discuss projections relevant for measurements at Belle II, both with and without electron polarization, and outline the necessary steps for a generalization to next-to-next-to-leading order.

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

163 extracted references · 7 canonical work pages

  1. [102]

    Crivellin, M

    A. Crivellin, M. Hoferichter, and J. M. Roney, Phys. Rev. D106, 093007 (2022), arXiv:2111.10378 [hep-ph]

  2. [1]

    J. S. Schwinger, Phys. Rev.73, 416 (1948). – 24 –

  3. [2]

    Kusch and H

    P. Kusch and H. M. Foley, Phys. Rev.74, 250 (1948)

  4. [3]

    R. H. Parker, C. Yu, W. Zhong, B. Estey, and H. Müller, Science360, 191 (2018), arXiv:1812.04130 [physics.atom-ph]

  5. [4]

    Morel, Z

    L. Morel, Z. Yao, P. Cladé, and S. Guellati-Khélifa, Nature588, 61 (2020)

  6. [5]

    Aoyama, T

    T. Aoyama, T. Kinoshita, and M. Nio, Atoms7, 28 (2019)

  7. [6]

    Volkov, Phys

    S. Volkov, Phys. Rev. D100, 096004 (2019), arXiv:1909.08015 [hep-ph]

  8. [7]

    Volkov, Phys

    S. Volkov, Phys. Rev. D110, 036001 (2024), arXiv:2404.00649 [hep-ph]

Show all 163 references
  1. [8]

    Aoyama, M

    T. Aoyama, M. Hayakawa, A. Hirayama, and M. Nio, Phys. Rev. D111, L031902 (2025), arXiv:2412.06473 [hep-ph]

  2. [9]

    Di Luzio, A

    L. Di Luzio, A. Keshavarzi, A. Masiero, and P. Paradisi, Phys. Rev. Lett.134, 011902 (2025), arXiv:2408.01123 [hep-ph]

  3. [10]

    X. Fan, T. G. Myers, B. A. D. Sukra, and G. Gabrielse, Phys. Rev. Lett.130, 071801 (2023), arXiv:2209.13084 [physics.atom-ph]

  4. [11]

    D. P. Aguillardet al.(Muon g− 2), Phys. Rev. Lett.131, 161802 (2023), arXiv:2308.06230 [hep-ex]

  5. [12]

    D. P. Aguillardet al.(Muon g− 2), Phys. Rev. D110, 032009 (2024), arXiv:2402.15410 [hep-ex]

  6. [13]

    Aoyamaet al., Phys

    T. Aoyamaet al., Phys. Rept.887, 1 (2020), arXiv:2006.04822 [hep-ph]

  7. [14]

    Aoyama, M

    T. Aoyama, M. Hayakawa, T. Kinoshita, and M. Nio, Phys. Rev. Lett.109, 111808 (2012), arXiv:1205.5370 [hep-ph]

  8. [15]

    Czarnecki, W

    A. Czarnecki, W. J. Marciano, and A. Vainshtein, Phys. Rev. D67, 073006 (2003), [Erratum: Phys. Rev. D73, 119901 (2006)], arXiv:hep-ph/0212229 [hep-ph]

  9. [16]

    Gnendiger, D

    C. Gnendiger, D. Stöckinger, and H. Stöckinger-Kim, Phys. Rev. D88, 053005 (2013), arXiv:1306.5546 [hep-ph]

  10. [17]

    Davier, A

    M. Davier, A. Hoecker, B. Malaescu, and Z. Zhang, Eur. Phys. J. C77, 827 (2017), arXiv:1706.09436 [hep-ph]

  11. [18]

    Keshavarzi, D

    A. Keshavarzi, D. Nomura, and T. Teubner, Phys. Rev. D97, 114025 (2018), arXiv:1802.02995 [hep-ph]

  12. [19]

    Colangelo, M

    G. Colangelo, M. Hoferichter, and P. Stoffer, JHEP02, 006 (2019), arXiv:1810.00007 [hep-ph]

  13. [20]

    Hoferichter, B.-L

    M. Hoferichter, B.-L. Hoid, and B. Kubis, JHEP08, 137 (2019), arXiv:1907.01556 [hep-ph]

  14. [21]

    Davier, A

    M. Davier, A. Hoecker, B. Malaescu, and Z. Zhang, Eur. Phys. J. C80, 241 (2020), [Erratum: Eur. Phys. J. C80, 410 (2020)], arXiv:1908.00921 [hep-ph]

  15. [22]

    Keshavarzi, D

    A. Keshavarzi, D. Nomura, and T. Teubner, Phys. Rev. D101, 014029 (2020), arXiv:1911.00367 [hep-ph]

  16. [23]

    B.-L. Hoid, M. Hoferichter, and B. Kubis, Eur. Phys. J. C80, 988 (2020), arXiv:2007.12696 [hep-ph]

  17. [24]

    A. Kurz, T. Liu, P. Marquard, and M. Steinhauser, Phys. Lett. B734, 144 (2014), arXiv:1403.6400 [hep-ph]. – 25 –

  18. [25]

    Melnikov and A

    K. Melnikov and A. Vainshtein, Phys. Rev. D70, 113006 (2004), arXiv:hep-ph/0312226 [hep-ph]

  19. [26]

    Colangelo, M

    G. Colangelo, M. Hoferichter, M. Procura, and P. Stoffer, JHEP09, 091 (2014), arXiv:1402.7081 [hep-ph]

  20. [27]

    Colangelo, M

    G. Colangelo, M. Hoferichter, B. Kubis, M. Procura, and P. Stoffer, Phys. Lett. B738, 6 (2014), arXiv:1408.2517 [hep-ph]

  21. [28]

    Colangelo, M

    G. Colangelo, M. Hoferichter, M. Procura, and P. Stoffer, JHEP09, 074 (2015), arXiv:1506.01386 [hep-ph]

  22. [29]

    Masjuan and P

    P. Masjuan and P. Sánchez-Puertas, Phys. Rev. D95, 054026 (2017), arXiv:1701.05829 [hep-ph]

  23. [30]

    Colangelo, M

    G. Colangelo, M. Hoferichter, M. Procura, and P. Stoffer, Phys. Rev. Lett.118, 232001 (2017), arXiv:1701.06554 [hep-ph]

  24. [31]

    Colangelo, M

    G. Colangelo, M. Hoferichter, M. Procura, and P. Stoffer, JHEP04, 161 (2017), arXiv:1702.07347 [hep-ph]

  25. [32]

    Hoferichter, B.-L

    M. Hoferichter, B.-L. Hoid, B. Kubis, S. Leupold, and S. P. Schneider, Phys. Rev. Lett. 121, 112002 (2018), arXiv:1805.01471 [hep-ph]

  26. [33]

    Hoferichter, B.-L

    M. Hoferichter, B.-L. Hoid, B. Kubis, S. Leupold, and S. P. Schneider, JHEP10, 141 (2018), arXiv:1808.04823 [hep-ph]

  27. [34]

    Gérardin, H

    A. Gérardin, H. B. Meyer, and A. Nyffeler, Phys. Rev. D100, 034520 (2019), arXiv:1903.09471 [hep-lat]

  28. [35]

    Bijnens, N

    J. Bijnens, N. Hermansson-Truedsson, and A. Rodríguez-Sánchez, Phys. Lett. B798, 134994 (2019), arXiv:1908.03331 [hep-ph]

  29. [36]

    Colangelo, F

    G. Colangelo, F. Hagelstein, M. Hoferichter, L. Laub, and P. Stoffer, Phys. Rev. D101, 051501 (2020), arXiv:1910.11881 [hep-ph]

  30. [37]

    Colangelo, F

    G. Colangelo, F. Hagelstein, M. Hoferichter, L. Laub, and P. Stoffer, JHEP03, 101 (2020), arXiv:1910.13432 [hep-ph]

  31. [38]

    T. Blum, N. Christ, M. Hayakawa, T. Izubuchi, L. Jin, C. Jung, and C. Lehner, Phys. Rev. Lett. 124, 132002 (2020), arXiv:1911.08123 [hep-lat]

  32. [39]

    Colangelo, M

    G. Colangelo, M. Hoferichter, A. Nyffeler, M. Passera, and P. Stoffer, Phys. Lett. B735, 90 (2014), arXiv:1403.7512 [hep-ph]

  33. [40]

    F. V. Ignatovet al.(CMD-3), Phys. Rev. D109, 112002 (2024), arXiv:2302.08834 [hep-ex]

  34. [41]

    F. V. Ignatovet al.(CMD-3), Phys. Rev. Lett.132, 231903 (2024), arXiv:2309.12910 [hep-ex]

  35. [42]

    Borsanyiet al., Nature 593, 51 (2021), arXiv:2002.12347 [hep-lat]

    S. Borsanyiet al., Nature 593, 51 (2021), arXiv:2002.12347 [hep-lat]

  36. [43]

    Boccalettiet al., (2024), arXiv:2407.10913 [hep-lat]

    A. Boccalettiet al., (2024), arXiv:2407.10913 [hep-lat]

  37. [44]

    Blumet al.(RBC, UKQCD), Phys

    T. Blumet al.(RBC, UKQCD), Phys. Rev. Lett.134, 201901 (2025), arXiv:2410.20590 [hep-lat]

  38. [45]

    Djukanovic, G

    D. Djukanovic, G. von Hippel, S. Kuberski, H. B. Meyer, N. Miller, K. Ottnad, J. Parrino, A. Risch, and H. Wittig, JHEP04, 098 (2025), arXiv:2411.07969 [hep-lat]. – 26 –

  39. [46]

    Bazavovet al.(Fermilab Lattice, HPQCD, MILC), Phys

    A. Bazavovet al.(Fermilab Lattice, HPQCD, MILC), Phys. Rev. Lett.135, 011901 (2025), arXiv:2412.18491 [hep-lat]

  40. [47]

    Campanario, H

    F. Campanario, H. Czyż, J. Gluza, T. Jeliński, G. Rodrigo, S. Tracz, and D. Zhuridov, Phys. Rev. D100, 076004 (2019), arXiv:1903.10197 [hep-ph]

  41. [48]

    Ignatov and R

    F. Ignatov and R. N. Lee, Phys. Lett. B833, 137283 (2022), arXiv:2204.12235 [hep-ph]

  42. [49]

    Colangelo, M

    G. Colangelo, M. Hoferichter, J. Monnard, and J. Ruiz de Elvira, JHEP08, 295 (2022), [Erratum: JHEP 03, 217 (2025)], arXiv:2207.03495 [hep-ph]

  43. [50]

    Monnard,Radiative corrections for the two-pion contribution to the hadronic vacuum polarization contribution to the muong− 2, Ph.D

    J. Monnard,Radiative corrections for the two-pion contribution to the hadronic vacuum polarization contribution to the muong− 2, Ph.D. thesis, Bern U. (2021)

  44. [51]

    Abbiendiet al., (2022), arXiv:2201.12102 [hep-ph]

    G. Abbiendiet al., (2022), arXiv:2201.12102 [hep-ph]

  45. [52]

    J. P. Leeset al.(BaBar), Phys. Rev. D108, L111103 (2023), arXiv:2308.05233 [hep-ex]

  46. [53]

    Budassi, C

    E. Budassi, C. M. Carloni Calame, M. Ghilardi, A. Gurgone, G. Montagna, M. Moretti, O. Nicrosini, F. Piccinini, and F. P. Ucci, JHEP05, 196 (2025), arXiv:2409.03469 [hep-ph]

  47. [54]

    Alibertiet al., SciPost Phys

    R. Alibertiet al., SciPost Phys. Comm. Rep.9, 1 (2025), arXiv:2410.22882 [hep-ph]

  48. [55]

    Crivellin, M

    A. Crivellin, M. Hoferichter, C. A. Manzari, and M. Montull, Phys. Rev. Lett.125, 091801 (2020), arXiv:2003.04886 [hep-ph]

  49. [56]

    Keshavarzi, W

    A. Keshavarzi, W. J. Marciano, M. Passera, and A. Sirlin, Phys. Rev. D102, 033002 (2020), arXiv:2006.12666 [hep-ph]

  50. [57]

    Malaescu and M

    B. Malaescu and M. Schott, Eur. Phys. J. C81, 46 (2021), arXiv:2008.08107 [hep-ph]

  51. [58]

    Colangelo, M

    G. Colangelo, M. Hoferichter, and P. Stoffer, Phys. Lett. B814, 136073 (2021), arXiv:2010.07943 [hep-ph]

  52. [59]

    Colangelo, A

    G. Colangelo, A. X. El-Khadra, M. Hoferichter, A. Keshavarzi, C. Lehner, P. Stoffer, and T. Teubner, Phys. Lett. B833, 137313 (2022), arXiv:2205.12963 [hep-ph]

  53. [60]

    Colangelo, M

    G. Colangelo, M. Hoferichter, B. Kubis, and P. Stoffer, JHEP10, 032 (2022), arXiv:2208.08993 [hep-ph]

  54. [61]

    Hoferichter, G

    M. Hoferichter, G. Colangelo, B.-L. Hoid, B. Kubis, J. Ruiz de Elvira, D. Schuh, D. Stamen, and P. Stoffer, Phys. Rev. Lett.131, 161905 (2023), arXiv:2307.02532 [hep-ph]

  55. [62]

    Stoffer, G

    P. Stoffer, G. Colangelo, and M. Hoferichter, JINST18, C10021 (2023), arXiv:2308.04217 [hep-ph]

  56. [63]

    T. P. Leplumey and P. Stoffer, (2025), arXiv:2501.09643 [hep-ph]

  57. [64]

    Hoferichter, B.-L

    M. Hoferichter, B.-L. Hoid, and B. Kubis, JHEP07, 095 (2025), arXiv:2504.13827 [hep-ph]

  58. [65]

    C. M. Carloni Calame, M. Passera, L. Trentadue, and G. Venanzoni, Phys. Lett. B746, 325 (2015), arXiv:1504.02228 [hep-ph]

  59. [66]

    Abbiendiet al.(MUonE), Eur

    G. Abbiendiet al.(MUonE), Eur. Phys. J. C77, 139 (2017), arXiv:1609.08987 [hep-ex]

  60. [67]

    Abbiendiet al.(MUonE), Letter of Intent: the MUonE project, Tech

    G. Abbiendiet al.(MUonE), Letter of Intent: the MUonE project, Tech. Rep. CERN-SPSC-2019-026, SPSC-I-252 (2019)

  61. [68]

    Banerjeeet al., Eur

    P. Banerjeeet al., Eur. Phys. J. C80, 591 (2020), arXiv:2004.13663 [hep-ph]

  62. [69]

    Bijnens, N

    J. Bijnens, N. Hermansson-Truedsson, L. Laub, and A. Rodríguez-Sánchez, JHEP04, 240 (2021), arXiv:2101.09169 [hep-ph]. – 27 –

  63. [70]

    E.-H. Chao, R. J. Hudspith, A. Gérardin, J. R. Green, H. B. Meyer, and K. Ottnad, Eur. Phys. J. C81, 651 (2021), arXiv:2104.02632 [hep-lat]

  64. [71]

    T. Blum, N. Christ, M. Hayakawa, T. Izubuchi, L. Jin, C. Jung, C. Lehner, and C. Tu (RBC, UKQCD), Phys. Rev. D111, 014501 (2025), arXiv:2304.04423 [hep-lat]

  65. [72]

    Lüdtke, M

    J. Lüdtke, M. Procura, and P. Stoffer, JHEP04, 125 (2023), arXiv:2302.12264 [hep-ph]

  66. [73]

    Hoferichter, P

    M. Hoferichter, P. Stoffer, and M. Zillinger, JHEP04, 092 (2024), arXiv:2402.14060 [hep-ph]

  67. [74]

    Lüdtke, M

    J. Lüdtke, M. Procura, and P. Stoffer, JHEP04, 130 (2025), arXiv:2410.11946 [hep-ph]

  68. [75]

    S. Holz, M. Hoferichter, B.-L. Hoid, and B. Kubis, Phys. Rev. Lett.134, 171902 (2025), arXiv:2411.08098 [hep-ph]

  69. [76]

    Bijnens, N

    J. Bijnens, N. Hermansson-Truedsson, and A. Rodríguez-Sánchez, JHEP03, 094 (2025), arXiv:2411.09578 [hep-ph]

  70. [77]

    Fodor, A

    Z. Fodor, A. Gérardin, L. Lellouch, K. K. Szabo, B. C. Toth, and C. Zimmermann, Phys. Rev. D 111, 114509 (2025), arXiv:2411.11719 [hep-lat]

  71. [78]

    Hoferichter, P

    M. Hoferichter, P. Stoffer, and M. Zillinger, JHEP02, 121 (2025), arXiv:2412.00178 [hep-ph]

  72. [79]

    Hoferichter, P

    M. Hoferichter, P. Stoffer, and M. Zillinger, Phys. Rev. Lett.134, 061902 (2025), arXiv:2412.00190 [hep-ph]

  73. [80]

    S. Holz, M. Hoferichter, B.-L. Hoid, and B. Kubis, JHEP04, 147 (2025), arXiv:2412.16281 [hep-ph]

  74. [81]

    Hoferichter, J

    M. Hoferichter, J. Lüdtke, L. Naterop, M. Procura, and P. Stoffer, Phys. Rev. Lett.134, 201801 (2025), arXiv:2503.04883 [hep-ph]

  75. [82]

    Colangeloet al., (2022), arXiv:2203.15810 [hep-ph]

    G. Colangeloet al., (2022), arXiv:2203.15810 [hep-ph]

  76. [83]

    Aibaet al., (2021), arXiv:2111.05788 [hep-ex]

    M. Aibaet al., (2021), arXiv:2111.05788 [hep-ex]

  77. [84]

    D. P. Aguillardet al.(Muon g− 2), (2025), arXiv:2506.03069 [hep-ex]

  78. [85]

    Alibertiet al., (2025), arXiv:2505.21476 [hep-ph]

    R. Alibertiet al., (2025), arXiv:2505.21476 [hep-ph]

  79. [86]

    Eidelman and M

    S. Eidelman and M. Passera, Mod. Phys. Lett. A22, 159 (2007), arXiv:hep-ph/0701260

  80. [87]

    Eidelman, D

    S. Eidelman, D. Epifanov, M. Fael, L. Mercolli, and M. Passera, JHEP03, 140 (2016), arXiv:1601.07987 [hep-ph]

  81. [88]

    Hoferichter, P

    M. Hoferichter, P. Stoffer, and M. Zillinger, Phys. Lett. B866, 139565 (2025), arXiv:2504.10582 [hep-ph]

  82. [89]

    G. F. Giudice, P. Paradisi, and M. Passera, JHEP11, 113 (2012), arXiv:1208.6583 [hep-ph]

  83. [90]

    Crivellin, M

    A. Crivellin, M. Hoferichter, and P. Schmidt-Wellenburg, Phys. Rev. D98, 113002 (2018), arXiv:1807.11484 [hep-ph]

  84. [91]

    Crivellin and M

    A. Crivellin and M. Hoferichter, JHEP07, 135 (2021), arXiv:2104.03202 [hep-ph]

  85. [92]

    Athron, C

    P. Athron, C. Balázs, D. H. J. Jacob, W. Kotlarski, D. Stöckinger, and H. Stöckinger-Kim, JHEP 09, 080 (2021), arXiv:2104.03691 [hep-ph]

  86. [93]

    Abdallahet al.(DELPHI), Eur

    J. Abdallahet al.(DELPHI), Eur. Phys. J. C35, 159 (2004), arXiv:hep-ex/0406010. – 28 –

  87. [94]

    G. A. González-Sprinberg, A. Santamaria, and J. Vidal, Nucl. Phys. B582, 3 (2000), arXiv:hep-ph/0002203

  88. [95]

    Acciarriet al.(L3), Phys

    M. Acciarriet al.(L3), Phys. Lett. B426, 207 (1998)

  89. [96]

    Abeet al.(SLD), (1999), SLAC-PUB-8163

    K. Abeet al.(SLD), (1999), SLAC-PUB-8163

  90. [97]

    D. Abbaneoet al.(ALEPH, DELPHI, L3, OPAL, SLD Heavy Flavor Group, Electroweak Group, LEP Electroweak Working Group, SLD Heavy Flavor), (2000), SLAC-REPRINT-2000-098, CERN-EP-2000-016, CERN-L3-200

  91. [98]

    del Aguila, F

    F. del Aguila, F. Cornet, and J. I. Illana, Phys. Lett. B271, 256 (1991)

  92. [99]

    Aadet al.(ATLAS), Phys

    G. Aadet al.(ATLAS), Phys. Rev. Lett.131, 151802 (2023), arXiv:2204.13478 [hep-ex]

  93. [100]

    Tumasyanet al.(CMS), Phys

    A. Tumasyanet al.(CMS), Phys. Rev. Lett.131, 151803 (2023), arXiv:2206.05192 [nucl-ex]

  94. [101]

    Hayrapetyanet al.(CMS), Rept

    A. Hayrapetyanet al.(CMS), Rept. Prog. Phys.87, 107801 (2024), arXiv:2406.03975 [hep-ex]

  95. [103]

    Köksal, S

    M. Köksal, S. C. İnan, A. A. Billur, Y. Özgüven, and M. K. Bahar, Phys. Lett. B783, 375 (2018), arXiv:1711.02405 [hep-ph]

  96. [104]

    Gutiérrez-Rodríguez, M

    A. Gutiérrez-Rodríguez, M. Köksal, A. A. Billur, and M. A. Hernández-Ruíz, (2019), arXiv:1903.04135 [hep-ph]

  97. [105]

    Beresford and J

    L. Beresford and J. Liu, Phys. Rev. D102, 113008 (2020), arXiv:1908.05180 [hep-ph]

  98. [106]

    Dyndal, M

    M. Dyndal, M. Klusek-Gawenda, M. Schott, and A. Szczurek, Phys. Lett. B809, 135682 (2020), arXiv:2002.05503 [hep-ph]

  99. [107]

    Haisch, L

    U. Haisch, L. Schnell, and J. Weiss, SciPost Phys.16, 048 (2024), arXiv:2307.14133 [hep-ph]

  100. [108]

    D. Shao, B. Yan, S.-R. Yuan, and C. Zhang, Sci. China Phys. Mech. Astron.67, 281062 (2024), arXiv:2310.14153 [hep-ph]

  101. [109]

    Beresford, S

    L. Beresford, S. Clawson, and J. Liu, Phys. Rev. D110, 092016 (2024), arXiv:2403.06336 [hep-ph]

  102. [110]

    Dittmaier, T

    S. Dittmaier, T. Engel, J. L. H. Ariza, and M. Pellen, (2025), arXiv:2504.11391 [hep-ph]

  103. [111]

    Altmannshoferet al.(Belle-II), PTEP 2019, 123C01 (2019), [Erratum: PTEP2020, 029201 (2020)], arXiv:1808.10567 [hep-ex]

    W. Altmannshoferet al.(Belle-II), PTEP 2019, 123C01 (2019), [Erratum: PTEP2020, 029201 (2020)], arXiv:1808.10567 [hep-ex]

  104. [112]

    Chen and Y

    X. Chen and Y. Wu, JHEP10, 089 (2019), arXiv:1803.00501 [hep-ph]

  105. [113]

    H. M. Tran and Y. Kurihara, Eur. Phys. J. C81, 108 (2021), arXiv:2006.00660 [hep-ph]

  106. [114]

    Krinner and N

    F. Krinner and N. Kaiser, Eur. Phys. J. C82, 410 (2022), arXiv:2110.05358 [hep-ph]

  107. [115]

    Banerjee, A

    S. Banerjee, A. Y. Korchin, and Z. W¸ as, Phys. Rev. D106, 113010 (2022), arXiv:2209.06047 [hep-ph]

  108. [116]

    Banerjee, A

    S. Banerjee, A. Y. Korchin, E. Richter-W¸ as, and Z. W¸ as, Phys. Rev. D109, 013002 (2024), arXiv:2307.03526 [hep-ph]

  109. [117]

    Inamiet al.(Belle), Phys

    K. Inamiet al.(Belle), Phys. Lett. B551, 16 (2003), arXiv:hep-ex/0210066

  110. [118]

    Inamiet al.(Belle), JHEP 04, 110 (2022), arXiv:2108.11543 [hep-ex]

    K. Inamiet al.(Belle), JHEP 04, 110 (2022), arXiv:2108.11543 [hep-ex]. – 29 –

  111. [119]

    Bernabéu, G

    J. Bernabéu, G. A. González-Sprinberg, J. Papavassiliou, and J. Vidal, Nucl. Phys. B790, 160 (2008), arXiv:0707.2496 [hep-ph]

  112. [120]

    Bernabéu, G

    J. Bernabéu, G. A. González-Sprinberg, and J. Vidal, JHEP01, 062 (2009), arXiv:0807.2366 [hep-ph]

  113. [121]

    J. P. Leeset al.(BaBar), Phys. Rev. Lett.125, 241801 (2020), arXiv:2005.01230 [hep-ex]

  114. [122]

    D. M. Asneret al.(US Belle II Group, Belle II/SuperKEKB e- Polarization Upgrade Working Group), (2022), arXiv:2205.12847 [physics.acc-ph]

  115. [123]

    Aiharaet al., (2024), arXiv:2406.19421 [hep-ex]

    H. Aiharaet al., (2024), arXiv:2406.19421 [hep-ex]

  116. [124]

    Hahn, Comput

    T. Hahn, Comput. Phys. Commun.140, 418 (2001), arXiv:hep-ph/0012260

  117. [125]

    Mertig, M

    R. Mertig, M. Bohm, and A. Denner, Comput. Phys. Commun.64, 345 (1991)

  118. [126]

    H. H. Patel, Comput. Phys. Commun.218, 66 (2017), arXiv:1612.00009 [hep-ph]

  119. [127]

    Shtabovenko, Comput

    V. Shtabovenko, Comput. Phys. Commun.218, 48 (2017), arXiv:1611.06793 [physics.comp-ph]

  120. [128]

    R. A. Fazio, P. Mastrolia, E. Mirabella, and W. J. Torres Bobadilla, Eur. Phys. J. C74, 3197 (2014), arXiv:1404.4783 [hep-ph]

  121. [129]

    Banerjee, T

    P. Banerjee, T. Engel, A. Signer, and Y. Ulrich, SciPost Phys.9, 027 (2020), arXiv:2007.01654 [hep-ph]

  122. [130]

    Ulrich,McMule – QED Corrections for Low-Energy Experiments, Ph.D

    Y. Ulrich,McMule – QED Corrections for Low-Energy Experiments, Ph.D. thesis, Zurich U., Inst. Math. (2020), arXiv:2008.09383 [hep-ph]

  123. [131]

    Ulrich, (2025), arXiv:2501.03703 [hep-ph]

    Y. Ulrich, (2025), arXiv:2501.03703 [hep-ph]

  124. [132]

    Buccioni, S

    F. Buccioni, S. Pozzorini, and M. Zoller, Eur. Phys. J. C78, 70 (2018), arXiv:1710.11452 [hep-ph]

  125. [133]

    Buccioni, J.-N

    F. Buccioni, J.-N. Lang, J. M. Lindert, P. Maierhöfer, S. Pozzorini, H. Zhang, and M. F. Zoller, Eur. Phys. J. C79, 866 (2019), arXiv:1907.13071 [hep-ph]

  126. [134]

    G. P. Lepage, (1980), CLNS-80/447

  127. [135]

    Engel, A

    T. Engel, A. Signer, and Y. Ulrich, JHEP01, 085 (2020), arXiv:1909.10244 [hep-ph]

  128. [136]

    Frixione, Z

    S. Frixione, Z. Kunszt, and A. Signer, Nucl. Phys. B467, 399 (1996), arXiv:hep-ph/9512328

  129. [137]

    Frederix, S

    R. Frederix, S. Frixione, F. Maltoni, and T. Stelzer, JHEP10, 003 (2009), arXiv:0908.4272 [hep-ph]

  130. [138]

    Banerjee, T

    P. Banerjee, T. Engel, N. Schalch, A. Signer, and Y. Ulrich, Phys. Lett. B820, 136547 (2021), arXiv:2106.07469 [hep-ph]

  131. [139]

    Engel, A

    T. Engel, A. Signer, and Y. Ulrich, JHEP04, 097 (2022), arXiv:2112.07570 [hep-ph]

  132. [140]

    Broggioet al., JHEP 01, 112 (2023), arXiv:2212.06481 [hep-ph]

    A. Broggioet al., JHEP 01, 112 (2023), arXiv:2212.06481 [hep-ph]

  133. [141]

    Kollatzsch and Y

    S. Kollatzsch and Y. Ulrich, SciPost Phys.15, 104 (2023), arXiv:2210.17172 [hep-ph]

  134. [142]

    Tsai, Phys

    Y.-S. Tsai, Phys. Rev. D4, 2821 (1971), [Erratum: Phys. Rev. D13, 771 (1976)]

  135. [143]

    Pospelov and A

    M. Pospelov and A. Ritz, Phys. Rev. D89, 056006 (2014), arXiv:1311.5537 [hep-ph]

  136. [144]

    Ghosh and R

    D. Ghosh and R. Sato, Phys. Lett. B777, 335 (2018), arXiv:1709.05866 [hep-ph]

  137. [145]

    J. H. Kühn, Phys. Lett. B313, 458 (1993), arXiv:hep-ph/9307269. – 30 –

  138. [146]

    Navaset al.(Particle Data Group), Phys

    S. Navaset al.(Particle Data Group), Phys. Rev. D110, 030001 (2024)

  139. [147]

    Bernabéu, G

    J. Bernabéu, G. A. González-Sprinberg, and J. Vidal, Phys. Lett. B326, 168 (1994)

  140. [148]

    Alemany, N

    R. Alemany, N. Rius, J. Bernabéu, J. J. Gómez-Cadenas, and A. Pich, Nucl. Phys. B379, 3 (1992)

  141. [149]

    Hagiwara, A

    K. Hagiwara, A. D. Martin, and D. Zeppenfeld, Phys. Lett. B235, 198 (1990)

  142. [150]

    Bernabéu, G

    J. Bernabéu, G. A. González-Sprinberg, M. Tung, and J. Vidal, Nucl. Phys. B436, 474 (1995), arXiv:hep-ph/9411289

  143. [151]

    J. F. Donoghue, E. Golowich, and B. R. Holstein,Dynamics of the standard model, Vol. 2 (CUP, 2014)

  144. [152]

    Abashianet al.(Belle), Nucl

    A. Abashianet al.(Belle), Nucl. Instrum. Meth. A479, 117 (2002)

  145. [153]

    Engel, C

    T. Engel, C. Gnendiger, A. Signer, and Y. Ulrich, JHEP02, 118 (2019), arXiv:1811.06461 [hep-ph]

  146. [154]

    Boncianiet al., Phys

    R. Boncianiet al., Phys. Rev. Lett.128, 022002 (2022), arXiv:2106.13179 [hep-ph]

  147. [155]

    M. F. Zoller, (2025), private communication

  148. [156]

    Bonocore and A

    D. Bonocore and A. Kulesza, Phys. Lett. B833, 137325 (2022), arXiv:2112.08329 [hep-ph]

  149. [157]

    Balsach, D

    R. Balsach, D. Bonocore, and A. Kulesza, Phys. Rev. D110, 016029 (2024), arXiv:2312.11386 [hep-ph]

  150. [158]

    Engel, JHEP07, 177 (2023), arXiv:2304.11689 [hep-ph]

    T. Engel, JHEP07, 177 (2023), arXiv:2304.11689 [hep-ph]

  151. [159]

    Dittmaier and C

    S. Dittmaier and C. Schwan, Eur. Phys. J. C76, 144 (2016), arXiv:1511.01698 [hep-ph]

  152. [160]

    Dittmaier, A

    S. Dittmaier, A. Huss, and C. Schwinn, Nucl. Phys. B885, 318 (2014), arXiv:1403.3216 [hep-ph]

  153. [161]

    Jadach, Z

    S. Jadach, Z. W¸ as, R. Decker, and J. H. Kühn, Comput. Phys. Commun.76, 361 (1993)

  154. [162]

    Chrzaszcz, T

    M. Chrzaszcz, T. Przedziński, Z. W¸ as, and J. Zaremba, Comput. Phys. Commun.232, 220 (2018), arXiv:1609.04617 [hep-ph]

  155. [163]

    R. K. Ellis and G. Zanderighi, JHEP02, 002 (2008), arXiv:0712.1851 [hep-ph]. – 31 –

Pith tools

Reviewed August 15, 2026 · model on record in the stance chip above.