Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Semianalytical estimates of scattering thresholds and gravitational
  radiation in ultrarelativistic black hole encounters   Ultrarelativistic collisions of black holes are ideal gedanken experiments to
study the nonlinearities of general relativity. In this paper we use
semianalytical tools to better understand the nature of these collisions and
the emitted gravitational radiation. We explain many features of the energy
spectra extracted from numerical relativity simulations using two complementary
semianalytical calculations. In the first calculation we estimate the radiation
by a "zero-frequency limit" analysis of the collision of two point particles
with finite impact parameter. In the second calculation we replace one of the
black holes by a point particle plunging with arbitrary energy and impact
parameter into a Schwarzschild black hole, and we explore the multipolar
structure of the radiation paying particular attention to the near-critical
regime. We also use a geodesic analogy to provide qualitative estimates of the
dependence of the scattering threshold on the black hole spin and on the
dimensionality of the spacetime.

13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
22
The categories of this paper are: chao-dyn
8
The categories of this paper are: hep-ex
4
The categories of this paper are: cond-mat
19
The categories of this paper are: eess
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph