tau -> (3 pions) nu_tau decays are analysed within the framework of the resonance effective theory of QCD. We work out the relevant Lagrangian that describes the axial-vector current hadronization contributing to these processes, in particular the local a_1(1260)-rho(770)-Goldstone interactions. The new coupling constants are constrained by imposing the asymptotic behaviour of the corresponding spectral function within QCD. Hence we compare the theoretical framework with the experimental data, obtaining a good quality fit from the ALEPH spectral function and branching ratio. We also get values for the mass and on-shell width of the a_1(1260) resonance. In this way we are able to provide the structure functions that have been measured by OPAL and CLEO-II and we find an excellent agreement.

D.G.D. acknowledges financial support from Fundación Antorchas and CONICET (Argentina). J.P. is supported by a ‘‘Ramón y Cajal’’ contract with CSIC funded by MCYT. This work has been supported in part by TMR EURIDICE, EC Contract No. HPRN-CT-2002-00311, by MCYT (Spain) under grant FPA2001-3031, by Generalitat Valenciana under grant GRUPOS03/013, by the Agencia Española de Cooperación Internacional (AECI) and by ERDF funds from the European Commission.

13 páginas, 7 figuras, 1 tabla.-- PACS number(s): 13.35.Dx, 11.30.Rd, 11.40.2q, 14.60.Fg.

Peer reviewed