Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravity-induced birefringence within the framework of Poincare gauge
  theory   Gauge theories of gravity provide an elegant and promising extension of
general relativity. In this paper we show that the Poincar\'e gauge theory
exhibits gravity-induced birefringence under the assumption of a specific gauge
invariant nonminimal coupling between torsion and Maxwell's field. Furthermore
we give for the first time an explicit expression for the induced phaseshift
between two orthogonal polarization modes within the Poincar\'e framework.
Since such a phaseshift can lead to a depolarization of light emitted from an
extended source this effect is, in principle, observable. We use white dwarf
polarimetric data to constrain the essential coupling constant responsible for
this effect.

10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th
27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci