Reducing hadronic uncertainty in low-energy neutral-current processes

We analyze the hadronic uncertainty from light-quark loops coupled to (anti)neutrino in low-energy neutral-current (anti)neutrino scattering, estimated at the 0.3 − 0.4 % level. This uncertainty arises from limited knowledge of the charge-isospin correlation function of quark currents. We study the charge-charge and charge-isospin correlators within SU(2) and SU(3) chiral perturbation theory (ChPT). In SU(2) ChPT, the two correlators are identical to all orders in the chiral and electromagnetic expansions. We further perform a leading-order SU(3) ChPT calculation and discuss the relevant counterterms. Our findings reduce the hadronic uncertainty in neutral-current processes such as (anti)neutrino-electron and coherent elastic (anti)neutrino-nucleus scattering by a factor ∼ 35.