  Motivated by recent studies of symmetry protected topological (SPT) phases,
we explore the possible gapless quantum disordered phases in the $(2+1)d$
nonlinear sigma model defined on the Grassmannian manifold
$\frac{U(N)}{U(n)\times U(N - n)}$ with a Wess-Zumino-Witten (WZW) term at
level $k$, which is the effective low energy field theory of the boundary of
certain $(3+1)d$ SPT states. With $k = 0$, this model has a well-controlled
large-$N$ limit, $i.e.$ its renormalization group equations can be computed
exactly with large-$N$. However, with the WZW term, the large-$N$ and large-$k$
limit alone is not sufficient for a reliable study of the nature of the quantum
disordered phase. We demonstrate that through a combined large-$N$, large-$k$
and $\epsilon-$generalization, a stable fixed point in the quantum disordered
phase can be reliably located in the large$-N$ limit and leading order
$\epsilon-$expansion, which corresponds to a $(2+1)d$ strongly interacting
conformal field theory.
