The spin-flavor dependence of nuclear forces from large-N QCD

We show that nuclear interactions are SU(4) symmetric at leading order in chiral perturbation theory in the large-N limit of QCD. The nucleons and delta resonances form a 20-dimensional representation of SU(4) and we show how Wignerʹs supermultiplet symmetry SU(4)sm, under which the nucleons transform as a 4-dimensional representation, follows as an accidental low energy symmetry. Exploiting SU(4) symmetry allows one to express the 18 independent leading N, Δ interaction operators invariant under SU(2)I × SU(2)J in terms of only two couplings. The three flavor analogue allows one to express the 28 leading octet, decuplet interactions in terms of only two couplings, which has implications for hypernuclei and strangeness in “neutron” stars.