Alpha-alpha interaction with chiral two pion exchange and 8Be lifetime

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Assuming that alpha particles are described by a scalar-isoscalar chiral invariant heavy field it is shown how chiral symmetry determines the alpha-alpha interaction at long distances unambiguously from dimensional power counting of an effective chiral Lagrangean. The leading strong contribution is given by a two pion exchange potential which turns out to be attractive and singular at the origin, hence demanding renormalization. When 8Be is treated as a resonance state a model independent correlation between the Q-factor and lifetime 1/Gamma for the decay into two alpha particles arises. For parameters compatible with potential model analyses of low energy pi-alpha scattering it is found a Breit-Wigner width Gamma = 4.3(3) eV very close to the experimental value, Gamma= 5.57 (25)eV.