Large-N_c constraints for nuclear current operators

Low-energy nuclear physics is at the forefront of precision tests of the Standard Model and searches for new physics. Effective field theories (EFTs) provide a way to connect nuclear physics directly to the Standard Model at the cost of a large number of a priori undetermined couplings in the nuclear EFTs. In order to make reliable statements about the Standard Model and its possible extensions using nuclear systems, these couplings need to be determined from nonperturbative quantum chromodynamics (QCD) input. Ideally, lattice QCD caluclations would complete this task; however, these calculations are not yet possible for many couplings of interest. Therefore, constraints from other means are necessary for current experiments, and they could also guide future lattice calculations. One such tool is the large-N_c limit of QCD, where N_c is the number of colors. In this limit, new symmetries emerge in the baryon sector that constrain the couplings in the nuclear EFTs. Here, we discuss examples of these constraints for few-body currents relevant for processes in and beyond the Standard Model with a particular emphasis on neutrinoless double beta decay.