Shell model Monte Carlo method for two-neutrino double beta decay.

Shell model Monte Carlo techniques are used to calculate two-neutrino double beta decay matrix elements. We test the approach against direct diagonalization for 48Ca in the complete pf shell using the KB3 interaction. The method is then applied to the decay of 76Ge in the (0f5/2,1p,0g9/2) model space using a newly calculated realistic interaction. Our result for the matrix element is 0.12±0.05 MeV-1, in reasonable agreement with the experimental value.