Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The mystery of cosmological vacuum energy density and the accelerated
  expansion of the universe   The principles of General Relativity allow for a non-vanishing cosmological
constant, which can possibly be interpreted at least partially in terms of
quantum-fluctuations of matter fields. Depending on sign and magnitude it can
cause accelerated or decelerated expansion at certain stages of cosmic
evolution. Recent observations in cosmology seem to indicate that we presently
live in an accelerated phase. We recall the history and fundamental issues
connected with the cosmological constant and then discuss present evidences for
a positive value, which causes the accelerated expansion.

1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys