Light nuclei and their collisions from the inside out

The variational Monte Carlo and Green's function Monte Carlo methods have achieved great success in computing energy levels and transition rates in light nuclei, by use of random sampling of elaborate position-space wave functions instead of basis expansions. However, these methods present a distinct set of difficulties in applications to "long-range" wave function properties like scattering amplitudes and the large-radius tails of bound states. In particular, variational trial functions with strong clustering are difficult to produce, effective Monte Carlo sampling schemes for low-probability tails and "off-diagonal" quantities are hard to identify, and relatively inefficient diagonalization approaches to scattering are difficult to avoid. We will describe calculations that mitigate these difficulties by avoiding direct calculation of long-range amplitudes in the wave function and instead finding them from integrals over better-computed short-range parts of the wave function. Applications presented will include spectroscopic overlaps for one-nucleon and alpha-particle removal, true scattering calculations in A = 4,5 systems, and scattering around A = 5 resonances using pseudo-bound variational wave functions.