Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Loop Quantum Gravity   This article presents an "in-a-nutshell" yet self-contained introductory
review on loop quantum gravity (LQG) -- a background-independent,
nonperturbative approach to a consistent quantum theory of gravity. Instead of
rigorous and systematic derivations, it aims to provide a general picture of
LQG, placing emphasis on the fundamental ideas and their significance. The
canonical formulation of LQG, as the central topic of the article, is presented
in a logically orderly fashion with moderate details, while the spin foam
theory, black hole thermodynamics, and loop quantum cosmology are covered
briefly. Current directions and open issues are also summarized.

24
The categories of this paper are: dg-ga
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
19
The categories of this paper are: eess
2
The categories of this paper are: math
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat