Perturbative χEFT calculations of the deuteron and triton up to N²LO

We extend previous studies of the deuteron and triton ground-state energies to next-to-next-to-leading order (N²LO) in chiral effective field theory, employing a power counting in which subleading interactions are treated perturbatively. Triton calculations are performed using the no-core shell model, and we demonstrate converged perturbative results for regulator cutoffs up to Λ 1200 MeV. We analyze exceptional cutoffs in the ³P₀ and ³S₁ -³D₁ nucleon-nucleon channels and find a resulting cutoff dependence in the triton ground-state energy at N²LO. The effect associated with the exceptional cutoff in the ³P₀ channel can be mitigated by redefining the leading-order wave function within the freedom allowed by the effective field theory. The same approach applied in the ³S₁ -³D₁ channel remedies the effect of this exceptional cutoff on the ground state energy of the deuteron, but not for the triton.