Quark mass dependence of the rho and sigma from dispersion relations and   Chiral Perturbation Theory
  We use the one-loop Chiral Perturbation   Theory pion-pion scattering amplitude and dispersion theory in the form of the inverse amplitude method, to study the quark mass dependence of the two lightest resonances of the strong interactions, the f_0(600) (sigma) and the rho-meson. As main results we find that the rho-pion-pion coupling constant is almost quark mass independent and that the rho mass shows a smooth quark mass dependence while that of the sigma shows a strong non-analyticity. These findings are important for studies of the meson spectrum on the lattice. 
C. Hanhart, J. R. Pelaez and G.Rios