Extraction of a_nn from pi- d -> n n gamma
  I present a calculation of the pi- d -> n n gamma reaction to third order in chiral perturbation theory. The short-distance physics of this reaction can be constrained by relating it to several important low-energy weak reactions. The theoretical error in a_nn extracted from this reaction can thus be reduced by a factor larger than three to +-0.05 fm. 
Anders Gardestig