We propose a new theory framework to study the isospin-symmetry breaking
correction Ξ΄Cβ in superallowed nuclear beta decays, crucial for
the precise determination of β£Vudββ£. Based on a general assumptions of the
isovector dominance in ISB interactions, we construct a set of functions
FTzββ which involve nuclear matrix elements of isovector monopole operators
and the nuclear Green's function. Via the functions FTzββ, a connection of
Ξ΄Cβ to measurable electroweak nuclear radii is established,
providing an experimental gauge of the theory accuracy of Ξ΄Cβ. We
outline a strategy to perform ab-initio calculations of FTzββ based on the
Lanczos algorithm, and discuss its similarity with other
nuclear-structure-dependent inputs in nuclear beta decays.Comment: 8 pages, 1 tabl