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

We use chiral effective theory (χET) to predict the deuteron form factor ratio G_C/G_Q 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 G_Q(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 G_Q via a two-nucleon operator that couples to quadrupole photons. After that renormalization we obtain a robust prediction for the shape of G_C/G_Q 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 G_C/G_M.