Spurious Isospin Breaking in the In-medium Similarity Renormalization Group

TL;DR

This paper investigates artificial isospin symmetry breaking in the IMSRG method and proposes solutions to improve the accuracy of theoretical corrections in superallowed beta decay, crucial for CKM unitarity tests.

Contribution

It identifies sources of spurious isospin breaking in IMSRG calculations and offers strategies to mitigate these effects, enhancing the reliability of nuclear theory predictions.

Findings

Effective remedies reduce spurious isospin breaking in IMSRG

Improved accuracy in calculating $oldsymbol{ ext{delta}_C}$ corrections

Enhanced confidence in CKM unitarity tests

Abstract

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 $\delta_C$.