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The pole structure of the low energy $\pi\pi$ scattering amplitudes isstudied using a proper chiral unitarization method combined with crossingsymmetry and the low energy phase shift data. It is found that the $\sigma$pole position is at $M_\sigma=470\pm 50MeV$, $\Gamma_\sigma=570\pm 50MeV$. Theexistence of the virtual state pole in the IJ=20 channel is reconfirmed.Various threshold parameters are estimated and are found in general in goodagreement with the results obtained from the Roy equation analyses.Comment: Minor corrections made and references added. Final version accepted  for publication as JHEP02(2005)04

The pole structure of the unitary, crossing symmetric low energy ππ scattering amplitudes