Eur. Phys. J. C (2013) 73: 2528
https://doi.org/10.1140/epjc/s10052-013-2528-1

Regular Article - Theoretical Physics

Dispersive representation of the pion vector form factor in τ→ππν _τ decays

¹ IFLP, CONICET, Departamento de Física, Universidad Nacional de La Plata, C.C. 67, 1900, La Plata, Argentina
² Grup de Física Teòrica, Institut de Física d’Altes Energies, Universitat Autònoma de Barcelona, Bellaterra, 08193, Barcelona, Spain

^* e-mail: proig@ifae.es

Received: 26 March 2013
Revised: 11 July 2013
Published online: 23 August 2013

Abstract

We propose a dispersive representation of the charged pion vector form factor that is consistent with chiral symmetry and fulfills the constraints imposed by analyticity and unitarity. Unknown parameters are fitted to the very precise data on τ ⁻→π ⁻ π ⁰ ν _τ decays obtained by Belle, leading to a good description of the corresponding spectral function up to a ππ squared invariant mass s≃1.5 GeV². We determine the ρ(770) mass and width pole parameters and obtain the values of low-energy observables. The significance of isospin-breaking corrections is also discussed. For larger values of s, this representation is complemented with a phenomenological description to allow its implementation in the new TAUOLA hadronic currents.