Fusion and Statistics

It is becoming possible to simulate nuclear reactions in terms of quarks and gluons. I have recently calculated the proton-proton fusion and tritium beta decay rates with the NPLQCD collaboration. Our proton-proton fusion results can be extrapolated to physically light quark masses by isolating short-distance contact operators. This allows an extraction of two-body axial currents probed by MuSun and other experiments. Extending studies of nuclear reactions in lattice QCD to larger nuclei and lighter quarks still faces challenges, in particular the so-called signal-to-noise problem. I will also discuss random walk structures recently found in Monte Carlo probability distributions that suggest alternative statistical methods capable of avoiding the signal-to-noise problem for at least the simplest nucleon observables.