On the quark mass dependence of nucleon-nucleon S-wave scattering lengths

In the framework of a Chiral effective theory with dibaryon fields, we calculate the pion mass dependence of the inverse scattering length of the nucleon-nucleon system in the ${}^3{S}_1$ channel at order ${(m_\pi^3 / \Lambda_\chi^2)}\times (m_\pi^{1/2}m_N^{3/2}/8\pi f_\pi^2)^n$forall$n\ge 0$. We show that certain sets of potentially large higher order contributions vanish. We discuss the difficulties of extending the proof to the ${}^1{S}_0$ channel. We apply our results to chiral extrapolations of current lattice data.