Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measurement of the dark matter velocity anisotropy in galaxy clusters   The internal dynamics of a dark matter structure may have the remarkable
property that the local temperature in the structure depends on direction. This
is parametrized by the velocity anisotropy beta which must be zero for relaxed
collisional structures, but has been shown to be non-zero in numerical
simulations of dark matter structures. Here we present a method to infer the
radial profile of the velocity anisotropy of the dark matter halo in a galaxy
cluster from X-ray observables of the intracluster gas. This non-parametric
method is based on a universal relation between the dark matter temperature and
the gas temperature which is confirmed through numerical simulations. We apply
this method to observational data and we find that beta is significantly
different from zero at intermediate radii. Thus we find a strong indication
that dark matter is effectively collisionless on the dynamical time-scale of
clusters, which implies an upper limit on the self-interaction cross-section
per unit mass sigma/m < 1 cm2/g. Our results may provide an independent way to
determine the stellar mass density in the central regions of a relaxed cluster,
as well as a test of whether a cluster is in fact relaxed.

11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
32
The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
2
The categories of this paper are: math
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
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