Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitoelectromagnetism: Basic principles, novel approaches and their
  application to Electromagnetism   This work is focused on the theory of Gravitoelectromagnetism (GEM). In the
first part of this work we present a brief review of gravitoelectromagnetism,
we locate and discuss all the problems which appear in this approach. We also
try to avoid these problems by proposing new approaches in which we use the
additional degrees of freedom of the gravitational field. In the second part of
this work, we review our previous work regarding the construction of a
tensorial theory, using the formalism of General Relativity, which aims to
describe the true electromagnetism. We also extend this theory in order to make
it more realistic. Finally in the third part of this work, we investigate the
existence of gravitational invariants similar to the electromagnetic ones.

16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
17
The categories of this paper are: q-fin
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph