  We study the dependence of the pion-pion scattering phase shifts on the light
quark mass in both standard and unitarized SU(2) Chiral Perturbation Theory
(ChPT) to one and two loops. We then use unitarized SU(3) ChPT to study the
elastic f_0(600), kappa(800), rho(770) and K*(892) resonances. The quark masses
are varied up to values of interest for lattice studies. We find a very soft
dependence on the light quark mass of the pion-pion phase shifts at one loop
and slightly stronger at two loops and a good agreement with lattice results.
The SU(3) analysis shows that the properties of the rho(770) and K*(892) depend
smoothly on the quark mass whereas the scalar resonances present a
non-analyticity at high quark masses. We also confirm the lattice assumption of
quark mass independence of the vector two-meson coupling that, however, is
violated for scalars.
