Quantum Monte Carlo calculations of electromagnetic transitions in low-lying states of $^8$Be*

We present quantum Monte Carlo calculations of electromagnetic transitions in low-lying states of $^8$Be. The Hamiltonian utilized to generate nuclear wave functions includes the Argonne-{\it v}18 two-nucleon and the Illinois-7 three-nucleon interactions. The M1 transition operator accounts for two-body contributions of one- and two-pion range, as well as contact terms, derived from chiral effective field theory. We find that two-body corrections are significant and always bring the theory in a better agreement with the experimental data. We also present E2 transition calculations, evaluated in impulse approximation, with emphasis on transitions involving the resonant excited states at $\sim 3$ MeV and $\sim 11$ MeV.