A new theoretical determination of Rτ /P (P = π, K)


  • Ignasi Rosell Universidad CEU Cardenal Herrera




Radiative decays, tau, pion, kaon, lepton universality, effective field theories, CKM unitarity, non-standard interactions


We have determined Rτ/P ≡ Γ(τ → P ντ [γ])/Γ(P → µνµ[γ]) (P = π, K). Whereas P decays are calculated by using Chiral Perturbation Theory (ChPT), τ decays have been studied with an effective approach where ChPT is enlarged by including the lightest resonances and following the high-energy behavior dictated by QCD. These ratios have allowed us to test the lepton universality and the CKM unitarity and also to search for bounds on non-standard interactions. Our results, δRτ/π = (0.18±0.57)% and δRτ/K = (0.97±0.58)%, are consistent with the previous theoretical determinations, but with much more robust assumptions, yielding a reliable uncertainty.


W. J. Marciano and A. Sirlin, Phys. Rev. Lett. 71 (1993), 3629- 3632.

R. Decker and M. Finkemeier, Phys. Lett. B 316 (1993), 403-406 [arXiv:hep-ph/9307372 [hep-ph]]; Phys. Lett. B 334 (1994), 199-202; Nucl. Phys. B 438 (1995), 17-53 [arXiv:hepph/9403385 [hep-ph]]; Nucl. Phys. B Proc. Suppl. 40 (1995), 453-461 [arXiv:hep-ph/9411316 [hep-ph]].

M. A. Arroyo-Ureña, G. Hernández-Tomé, G. López-Castro, ´ P. Roig and I. Rosell, Phys. Rev. D 104 (2021) no.9, L091502 [arXiv:2107.04603 [hep-ph]]; [arXiv:2112.01859 [hep-ph]].

Y. S. Amhis et al. [HFLAV], Eur. Phys. J. C 81 (2021) no.3, 226 [arXiv:1909.12524 [hep-ex]].

G. Aad et al. [ATLAS], Nature Phys. 17 (2021) no.7, 813-818 [arXiv:2007.14040 [hep-ex]].

CMS Collaboration (2021), “A precision measurement of the W boson decay branching fractions in pp collisions at √ s = 13 TeV,” CMS-PAS-SMP-18-011.

A. Pich, Prog. Part. Nucl. Phys. 75 (2014), 41-85 [arXiv:1310.7922 [hep-ph]].

V. Cirigliano, J. Jenkins and M. González-Alonso, Nucl. ´ Phys. B 830 (2010), 95-115 [arXiv:0908.1754 [hep-ph]]; M. González-Alonso and J. Martín Camalich, JHEP 12 (2016), 052 [arXiv:1605.07114 [hep-ph]].

V. Cirigliano, A. Falkowski, M. González-Alonso and A. Rodríguez-Sanchez, Phys. Rev. Lett. ´ 122 (2019) no.22, 221801 [arXiv:1809.01161 [hep-ph]].

S. González-Solís, A. Miranda, J. Rendon and P. Roig, Phys. Lett. B 804 (2020), 135371 [arXiv:1912.08725 [hep-ph]].

J. Gasser and H. Leutwyler, Annals Phys. 158 (1984) 142; Nucl. Phys. B 250 (1985) 465; Nucl. Phys. B 250 (1985) 517.

G. Ecker, J. Gasser, A. Pich and E. de Rafael, Nucl. Phys. B 321 (1989), 311-342; G. Ecker, J. Gasser, H. Leutwyler, A. Pich and E. de Rafael, Phys. Lett. B 223 (1989), 425-432; V. Cirigliano, G. Ecker, M. Eidemuller, R. Kaiser, A. Pich and ¨ J. Portoles, Nucl. Phys. B 753 (2006), 139-177 [arXiv:hepph/0603205 [hep-ph]].

V. Cirigliano and I. Rosell, Phys. Rev. Lett. 99 (2007), 231801 [arXiv:0707.3439 [hep-ph]].

V. Cirigliano and I. Rosell, JHEP 10 (2007), 005 [arXiv:0707.4464 [hep-ph]].

T. Kinoshita, Phys. Rev. Lett. 2 (1959), 477.

Z. H. Guo and P. Roig, Phys. Rev. D 82 (2010), 113016 [arXiv:1009.2542 [hep-ph]].

A. Guevara, G. López Castro and P. Roig, Phys. Rev. D 88 (2013) no.3, 033007 [arXiv:1306.1732 [hep-ph]]; [arXiv:2111.09994 [hep-ph]].

C. Y. Seng, D. Galviz, W. J. Marciano and U. G. Meißner, “An update on |Vus| and |Vus/Vud| from semileptonic kaon and pion decays,” [arXiv:2107.14708 [hep-ph]].

E. Kou et al. [Belle-II], PTEP 2019 (2019) no.12, 123C01 [erratum: PTEP 2020 (2020) no.2, 029201] [arXiv:1808.10567 [hep-ex]].

P. A. Zyla et al. [Particle Data Group], PTEP 2020 (2020) no.8, 083C01.

J. C. Hardy and I. S. Towner, Phys. Rev. C 102 (2020) no.4, 045501. 22. S. Aoki et al. [Flavour Lattice Averaging Group], Eur. Phys. J. C 80 (2020) no.2, 113 [arXiv:1902.08191 [hep-lat]].




How to Cite

Rosell I. A new theoretical determination of Rτ /P (P = π, K). Supl. Rev. Mex. Fis. [Internet]. 2022 May 18 [cited 2024 May 29];3(3):0308047 1-5. Available from: https://rmf.smf.mx/ojs/index.php/rmf-s/article/view/6078