Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: General purpose ray-tracing and polarized radiative transfer in General
  Relativity   Ray-tracing is a central tool for constructing mock observations of compact
object emission and for comparing physical emission models with observations.
We present Arcmancer, a publicly available general ray-tracing and tensor
algebra library, written in C++ and providing a Python interface. Arcmancer
supports Riemannian and semi-Riemannian spaces of any dimension and metric, and
has novel features such as support for multiple simultaneous coordinate charts,
embedded geometric shapes, local coordinate systems and automatic parallel
propagation. The Arcmancer interface is extensively documented and
user-friendly. While these capabilities make the library well suited for a
large variety of problems in numerical geometry, the main focus of this paper
is in general relativistic polarized radiative transfer. The accuracy of the
code is demonstrated in several code tests and in a comparison with GRTRANS, an
existing ray-tracing code. We then use the library in several scenarios as a
way to showcase the wide applicability of the code. We study a thin
variable-geometry accretion disk model, and find that polarization carries
information of the inner disk opening angle. Next, we study rotating neutron
stars and determine that to obtain polarized light curves at better than
$\sim1\%$ level of accuracy, the rotation needs to be taken into account both
in the space-time metric as well as in the shape of the star. Finally, we
investigate the observational signatures of an accreting black hole lensed by
an orbiting black hole. We find that these systems exhibit a characteristic
asymmetric twin-peak profile both in flux and polarization properties.

26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
17
The categories of this paper are: q-fin