Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Non-minimal coupling for the gravitational and electromagnetic fields: A
  general system of equations   We establish a new self-consistent system of equations for the gravitational
and electromagnetic fields. The procedure is based on a non-minimal non-linear
extension of the standard Einstein-Hilbert-Maxwell action. General properties
of a three-parameter family of non-minimal linear models are discussed. In
addition, we show explicitly, that a static spherically symmetric charged
object can be described by a non-minimal model, second order in the derivatives
of the metric, when the susceptibility tensor is proportional to the
double-dual Riemann tensor

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The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
4
The categories of this paper are: cond-mat
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys