  Low-energy baryon-baryon interactions are calculated in a high-statistics
lattice QCD study on a single ensemble of anisotropic clover gauge-field
configurations at a pion mass of m_\pi ~ 390 MeV, a spatial volume of L^3 ~
(2.5 fm)^3, and a spatial lattice spacing of b~0.123 fm. L\"uscher's method is
used to extract nucleon-nucleon, hyperon-nucleon and hyperon-hyperon scattering
phase shifts at one momentum from the one- and two-baryon ground-state energies
in the lattice volume. The isospin-3/2 N\Sigma interactions are found to be
highly spin-dependent, and the interaction in the ^3S_1 channel is found to be
strong. In contrast, the N\Lambda interactions are found to be
spin-independent, within the uncertainties of the calculation, consistent with
the absence of one-pion-exchange. The only channel for which a negative
energy-shift is found is \Lambda\Lambda, indicating that the \Lambda\Lambda
interaction is attractive, as anticipated from model-dependent discussions
regarding the H-dibaryon. The NN scattering lengths are found to be small,
clearly indicating the absence of any fine-tuning in the NN-sector at this pion
mass. This is consistent with our previous Lattice QCD calculation of NN
interactions. The behavior of the signal-to-noise ratio in the baryon-baryon
correlation functions, and in the ratio of correlation functions that yields
the ground-state energy splitting is explored. In particular, focus is placed
on the window of time slices for which the signal-to-noise ratio does not
degrade exponentially, as this provides the opportunity to extract quantitative
information about multi-baryon systems.
