Remarkable coincidence for the top Yukawa coupling and an approximately   massless bound state
  We calculate, with several corrections, the non-relativistic binding by Higgs exchange and gluon exchange between six top and six anti-top quarks (actually replaced by left-handed b quarks from time to time). The remarkable result is that, within our calculational accuracy of the order of 14% in the top quark Yukawa coupling g_t, the experimental running top-quark Yukawa coupling g_t = 0.935 happens to have just that value which gives a perfect cancellation of the unbound mass = 12 top-quark masses by this binding energy. In other words the bound state is massless to the accuracy of our calculation. Our calculation is in disagreement with a similar calculation by Kuchiev et al., but this deviation may be explained by a phase transition. We and Kuchiev et al. compute on different sides of this phase transition. 
C. D. Froggatt and H. B. Nielsen