  Motivated by the numerical evidence of a continuous phase transition between
antiferromagnetic and paramagnetic phases in the half-filled SU(N) Hubbbard
model, we studied its low energy nonlinear sigma model defined on Grassman
manifold $U(N)/U(m)U(N-m)$ using the complex projective presentation, which is
a direct generalization of the widely studied CP$^{N-1}$ model (corresponding
to $m=1$). With the $1/N$ expansion technique up to the first order by fixing
$m$ in space dimension $2<d<4$, we calculate the critical exponents of the Neel
moment, which are found to be only functions of $m/N$. Our results indicate
that larger $m$ effectively reduces $N$ and thus brings stronger fluctuations
around the saddle point at $N=\infty$.
