Pion-less effective field theory on low-energy deuteron electrodisintegration

In view of its relation to Big Bang nucleosynthesis and a reported discrepancy between nuclear models and data taken at S-DALINAC, electro-induced deuteron breakup ²H(e,e^'p)n is studied at momentum transfer q<100 MeV and close to threshold in the low-energy nuclear effective field theory without dynamical pions, EFT(π /). The result at next-to-next-to-leading order (N²LO) for electric dipole currents and at next-to-leading order (NLO) for magnetic ones converges order-by-order better than quantitatively predicted and contains no free parameter. It is at this order determined by simple, well-known observables. Decomposing the triple differential cross section into the longitudinal-plus-transverse (L+T), transverse-transverse (TT), and longitudinal-transverse interference (LT) terms, we find excellent agreement with a potential-model calculation by Arenhövel and co-workers, based on the Bonn potential. Theory and data also agree well on σ_L+T. There is however no space on the theory side for the discrepancy of up to 30%(3σ) between theory and experiment in σ_LT. From universality of EFT(π /), we conclude that no theoretical approach with the correct deuteron asymptotic wave function can explain the data. Undetermined short-distance contributions that could affect σ_LT enter only at high orders (i.e., at the few-percent level). We notice some issues with the kinematics and normalization of the data reported.