Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Astrophysical black holes as natural laboratories for fundamental
  physics and strong-field gravity   Astrophysical tests of general relativity belong to two categories: 1)
"internal", i.e. consistency tests within the theory (for example, tests that
astrophysical black holes are indeed described by the Kerr solution and its
perturbations), or 2) "external", i.e. tests of the many proposed extensions of
the theory. I review some ways in which astrophysical black holes can be used
as natural laboratories for both "internal" and "external" tests of general
relativity. The examples provided here (ringdown tests of the black hole
"no-hair" theorem, bosonic superradiant instabilities in rotating black holes
and gravitational-wave tests of massive scalar-tensor theories) are shamelessly
biased towards recent research by myself and my collaborators. Hopefully this
colloquial introduction aimed mainly at astrophysicists will convince skeptics
(if there are any) that space-based detectors will be crucial to study
fundamental physics through gravitational-wave observations.

2
The categories of this paper are: math
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
13
The categories of this paper are: quant-ph
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
16
The categories of this paper are: stat
27
The categories of this paper are: comp-gas