Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A meron cluster solution for the sign problem of the two-dimensional
  O(3) model   The two-dimensional O(3) model at a vacuum angle theta=pi is investigated.
This model has a severe sign problem. By a Wolff cluster algorithm an integer
or half-integer topological charge is assigned to each cluster. The meron
clusters (clusters with half-integer topological charge) are used to construct
an improved estimator for the correlation function of two spins at theta=pi.
Only configurations with 0 and 2 merons contribute to this correlation
function.
  An algorithm, that generates configurations with only 0 and 2 merons, is
constructed and numerical simulations at theta=pi are performed.
  The numerical results indicate the presence of long range correlations at
theta=pi.

22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom