Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The sign problem in the $\epsilon$-regime of QCD   QCD in the $\epsilon$-regime at nonzero baryon chemical potential $\mu$ is
reviewed. The focus is on aspects of the sign problem which are relevant for
lattice QCD. It is discussed how spontaneous chiral symmetry breaking and the
sign problem are related through the spectrum of the Dirac operator. The
strength of the sign problem is linked to the quark mass and the chemical
potential. Specific implications for lattice QCD are discussed.

21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
16
The categories of this paper are: stat
2
The categories of this paper are: math