Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Classification of Standard Model Particles in $E_6$ Orbifold Grand
  Unified Theories   We classify the standard model fermions, which originate from bulk fields of
the $\bf{27}$ or $\bar{\bf{27}}$ representation after orbifold breaking, in
$E_6$ grand unified theories on 5 or 6-dimensional space-time, under the
condition that $q$, $e^c$ and $u^c$ survive as zero modes.

30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int