Large-Nc Relationships Among Two-Derivative Pionless EFT Couplings*

As the number of colors (Nc) becomes large, QCD develops an additional symmetry.  This symmetry can be used to relate otherwise unknown low-energy constants (LECs) in effective field theories (EFTs) of QCD. Corrections to the large-Nc limit are perturbative in 1/Nc.  We have used this large-Nc symmetry to make predictions for low-energy few-body parity-violation experiments, but sufficient data does not yet exist to test these predictions. Here we consider higher order (two derivative) large-Nc relationships and test them against existing parity-conserving two-nucleon scattering data.  We find agreement, but also note subtleties involving subtraction-point dependence when the LECs themselves are not observables.  This subtraction point-dependence is a typical feature of EFT LECs.