  The low-energy neutron-Sigma^- interactions determine, in part, the role of
the strange quark in dense matter, such as that found in astrophysical
environments. The scattering phase shifts for this system are obtained from a
numerical evaluation of the QCD path integral using the technique of Lattice
QCD. Our calculations, performed at a pion mass of m_pi ~ 389 MeV in two large
lattice volumes, and at one lattice spacing, are extrapolated to the physical
pion mass using effective field theory. The interactions determined from QCD
are consistent with those extracted from hyperon-nucleon experimental data
within uncertainties, and strengthen theoretical arguments that the strange
quark is a crucial component of dense nuclear matter.
