Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Smoothness of the Horizons of Multi-Black Hole Solutions   In a recent paper it was suggested that some multi-black hole solutions in
five or more dimensions have horizons that are not smooth. These black hole
configurations are solutions to $d$-dimensional Einstein gravity (with no
dilaton) and are extremally charged with a magnetic type $(d-2)$-form. In this
work these solutions will be investigated further. It will be shown that
although the curvature is bounded as the horizon of one of the black holes is
approached, some derivatives of the curvature are not. This shows that the
metric is not $C^{\infty },$ but rather it is only $C^k$ with $k$ finite. These
solutions are static so their lack of smoothness cannot be attributed to the
presence of radiation.

14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom