Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Parameterizations of black-hole spacetimes beyond circularity   We discuss parameterizations of black-hole spacetimes in and beyond General
Relativity in view of their symmetry constraints: within the class of
axisymmetric, stationary spacetimes, we propose a parameterization that
includes non-circular spacetimes, both in Boyer-Lindquist as well as in
horizon-penetrating coordinates. We show how existing parameterizations, which
make additional symmetry assumptions (first, circularity; second, a hidden
constant of motion), are included in the new parameterization. Further, we
explain why horizon-penetrating coordinates may be more suitable to
parameterize non-circular deviations from the Kerr geometry. Our investigation
is motivated by our result that the regular, spinning black-hole spacetimes
proposed in [1,2] are non-circular. This particular deviation from circularity
can result in cusps, a dent and an asymmetry in the photon rings surrounding
the black-hole shadow. Finally, we explore a new class of non-circular
deviations from Kerr black holes, which promote the spin parameter to a
function, and find indications that regularity cannot be achieved in this
setting. This result strengthens the case for regular black holes based on a
promotion of the mass parameter to a function.

6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg