Quark-mass dependence of two-nucleon scattering

Understanding how the properties of the visible Universe depend on the parameters of the Standard Model of particle physics requires ab initio theoretical computations. To that end, we investigate the quark-mass dependence of low-energy nucleon-nucleon scattering in the deuteron and dineutron channels. We perform lattice-QCD calculations at pion masses M_π≈ 200 and $280$ MeV and compare their results to phenomenology at the physical point and to a previous calculation at M_π≈ 710 MeV. Scattering amplitudes, phase shifts, and threshold parameters are determined from finite-volume spectra using quantization conditions that explicitly incorporate long-distance effects from one-pion exchange. We analyze the pion-mass dependence of scattering lengths and effective ranges using chiral effective field theory with Weinberg and Kaplan-Savage-Wise power countings. From this, we estimate the pion-mass derivatives of the inverse scattering lengths and binding momentum, at the physical point. Both power countings indicate that the deuteron unbinds near M_π≈ 220 MeV.