Chiral effective theory predictions for deuteron form factor ratios at low Q2

Abstract

We use chiral effective theory (χET) to predict the deuteron form factor ratio GC/GQ as well as ratios of deuteron to nucleon form factors. These ratios are calculated to next-to-next-to-leading order. At this order the chiral expansion for the NN isoscalar charge operator (including consistently calculated 1/M corrections) is a parameter-free prediction of the effective theory. Use of this operator in conjunction with NLO and NNLO χET wavefunctions produces results that are consistent with extant experimental data for Q2 < 0.35 GeV2. These wavefunctions predict a deuteron quadrupole moment GQ(Q2 = 0) = 0.278–0.282 fm2—with the variation arising from short-distance contributions to this quantity. The variation is of the same size as the discrepancy between the theoretical result and the experimental value. This motivates the renormalization of GQ via a two-nucleon operator that couples to quadrupole photons. After that renormalization we obtain a robust prediction for the shape of GC/GQ at Q2 < 0.3 GeV2. This allows us to make precise, model-independent predictions for the values of this ratio that will be measured at the lower end of the kinematic range explored at BLAST. We also present results for the ratio GC/GM.