Non-standard Schwinger fermionic representation of unitary group
  The non-standard Schwinger fermionic representation of the unitary group is studied by using $n$-fermion operators. One finds that the Schwinger fermionic representation of the U(n) group is not unique when $n\ge 3$. In general, based on $n$-fermion operators, the non-standard Schwinger fermionic representation of the U(n) group can be established in a uniform approach, where all the generators commute with the total number operators. The Schwinger fermionic representation of $U(C^{m}_{n})$ group is also discussed. 
Fu-Lin Zhang, and Jing-Ling Chen