Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topological terms of (2+1)d flag-manifold sigma models   We examine topological terms of $(2+1)$d sigma models and their consequences
in the light of classifications of invertible quantum field theories utilizing
bordism groups. In particular, we study the possible topological terms for the
$U(N)/U(1)^N$ flag-manifold sigma model in detail. We argue that the Hopf-like
term is absent, contrary to the expectation from a nontrivial homotopy group
$\pi_3(U(N)/U(1)^N)=\mathbb{Z}$, and thus skyrmions cannot become anyons with
arbitrary statistics. Instead, we find that there exist ${N(N-1)\over 2}-1$
types of Chern-Simons terms, some of which can turn skyrmions into fermions,
and we write down explicit forms of effective Lagrangians.

11
The categories of this paper are: hep-lat
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an