  We present results from an ab initio three-dimensional, multi-physics core
collapse supernova simulation for the case of a 15 M progenitor. Our simulation
includes multi-frequency neutrino transport with state-of-the-art neutrino
interactions in the "ray-by-ray" approximation, and approximate general
relativity. Our model exhibits a neutrino-driven explosion. The shock radius
begins an outward trajectory at approximately 275 ms after bounce, giving the
first indication of a developing explosion in the model. The onset of this
shock expansion is delayed relative to our two-dimensional counterpart model,
which begins at approximately 200 ms after core bounce. At a time of 441 ms
after bounce, the angle-averaged shock radius in our three-dimensional model
has reached 751 km. Further quantitative analysis of the outcomes in this model
must await further development of the post-bounce dynamics and a simulation
that will extend well beyond 1 s after stellar core bounce, based on the
results for the same progenitor in the context of our two-dimensional,
counterpart model. This more complete analysis will determine whether or not
the explosion is robust and whether or not observables such as the explosion
energy, 56Ni mass, etc. are in agreement with observations. Nonetheless, the
onset of explosion in our ab initio three-dimensional multi-physics model with
multi-frequency neutrino transport and general relativity is encouraging.
