Non-relativistic fermionic energy gap in the non-abelian gauge systems
  We demonstrate that the non-relativistic fermions open the energy gap when the SU(N) gauge bosons, mediating the interaction between fermions, acquire the mass. Surprisingly, even though there is the SU(N) gauge symmetry, there is always one fermionic energy gap which is not degenerate to the rest of the $N-1$ fermions for $N \ge 3$ in the fundamental representation. 
Bo-Jie Huang, Chyh-Hong Chern
cond-mat.str-el