Reanalysis of pion-pion phase shifts from K -> pi pi decays

We re-investigate the impact of isospin violation for extracting the s-wave pion pion scattering phase shift difference delta_0(M_K) - delta_2(M_K) from K -> pi pi decays. Compared to our previous analysis in 2003, more precise experimental data and improved knowledge of low-energy constants are used. In addition, we employ a more robust data-driven method to obtain the phase shift difference delta_0(M_K) - delta_2(M_K) = (52.5 \pm 0.8_{exp} \pm 2.8_{theor}) degrees.We are grateful to Gilberto Colangelo for communicating to us the value of of δ0(MK) obtained in Ref.[1]. We would also like to thank Hans Bijnens, Jürg Gasser, Peter Minkowski,Helmut Neufeld and Jorge Portolés for useful comments. This work has been supported in part by the EU Contract MRTN-CT-2006-035482 (FLAVIAnet), by MICINN, Spain [grants FPA2007-60323 and Consolider-Ingenio 2010 CSD2007-00042 CPAN] and by Generalitat Valenciana (PROMETEO/2008/069).Peer reviewe