Three - body force in the triton

We have derived a two-pion-exchange three-body potential by using a chiral-invariant Lagrangian for the pion-nucleon interaction. Only the three dominant lowest-order processes which give rise to a three-body interaction are included: (a) The second pion is emitted before the first pion is absorbed and the nucleon which emits the second pion goes into a positive-energy state; (b) one nucleon exchanges a $\rho$ meson with a pion; (c) one nucleon is scattered into an $N^{*}\mathrm{}\left(1236\right)\mathrm{}$. We then proceed to evaluate the contribution of this three-body potential to the binding energy of the triton using a variational triton wave function. It is found that the two-pion-exchange three-body potential gives a significant contribution (2.32 MeV) to the binding energy of a triton.