Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonminimal coupling for the gravitational and electromagnetic fields:
  Traversable electric wormholes   We discuss new exact solutions of a three-parameter nonminimal
Einstein-Maxwell model. The solutions describe static spherically symmetric
objects with and without center, supported by an electric field nonminimally
coupled to gravity. We focus on a unique one-parameter model, which admits an
exact solution for a traversable electrically charged wormhole connecting two
universes, one asymptotically flat the other asymptotically de Sitter ones. The
relation between the asymptotic mass and charge of the wormhole and its throat
radius is analyzed. The wormhole solution found is thus a nonminimal
realization of the idea of Wheeler about charge without charge and shows that,
if the world is somehow nonminimal in the coupling of gravity to
electromagnetism, then wormhole appearance, or perhaps construction, is
possible.

2
The categories of this paper are: math
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
21
The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
18
The categories of this paper are: econ
28
The categories of this paper are: alg-geom
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex