Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Bright Side of Dark Matter   We show that it is not possible in the absence of dark matter to construct a
four-dimensional metric that explains galactic observations. In particular, by
working with an effective potential it is shown that a metric which is
constructed to fit flat rotation curves in spiral galaxies leads to the wrong
sign for the bending of light i.e. repulsion instead of attraction. Hence,
without dark matter the motion of particles on galactic scales cannot be
explained in terms of geodesic motion on a four- dimensional metric. This
reveals a new bright side to dark matter: it is indispensable if we wish to
retain the cherished equivalence principle.

14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys