Quantum Monte Carlo calculations of electromagnetic moments and transitions are reported for $A\le 9$ nuclei. The realistic Argonne $v_{18}$ two-nucleon and Illinois-7 three-nucleon potentials are used to generate the nuclear wave functions. Contributions of two-body meson-exchange current (MEC) operators are included for magnetic moments and $M1$ transitions. The MEC operators have been derived in both a standard nuclear physics approach and a chiral effective field theory formulation with pions and nucleons including up to one-loop corrections. The two-body MEC contributions provide significant corrections and lead to very good agreement with experiment. Their effect is particularly pronounced in the $A=9$, $T=3/2$ systems, in which they provide up to $\sim 20\%$ ($\sim 40\%$) of the total predicted value for the ${}^9$Li (${}^9$C) magnetic moment.

• Received 13 December 2012

DOI:https://doi.org/10.1103/PhysRevC.87.035503