Spurious Isospin Breaking in the In-medium Similarity Renormalization Group

Robustly quantifying the uncertainty in the isospin-related theoretical correction $\delta_C$ to superallowed beta decay rates is vital for a correct assessment of CKM unitarity. To this end, we identify the sources of artificial or \textit{spurious} isospin symmetry breaking introduced by the IMSRG many-body framework at a computational level and provide remedies. We test our best policy for preventing spurious ISB by evaluating $\delta_C$.