Large-basis no-core shell-model calculations and their application to ¹⁰C →¹⁰B fermi beta decay

We use a 4Ω shell-model calculation with a two-body effective interaction derived microscopically from the Reid93 potential to calculate the isospin-mixing correction for the ¹⁰C→¹⁰B superallowed Fermi transition. The effective interaction takes into account the Coulomb potential as well as the charge dependence of T = 1 partial waves. Our results suggest the isospin-mixing correction δ_C ≈ 0.1%, which is compatible with previous calculations obtained by other methods. The obtained δ_C correction is about a factor of four too small to obtain unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present experimental data.