K π vector form factor, dispersive constraints and τ→ν τ K π decays Diogo R. Boito, Rafel Escribano and Matthias Jamin Eur. Phys. J. C, 59 4 (2009) 821-829 Published online: 16 December 2008 DOI: 10.1140/epjc/s10052-008-0834-9