Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Theory and simulation of two-dimensional nematic and tetratic phases   Recent experiments and simulations have shown that two-dimensional systems
can form tetratic phases with four-fold rotational symmetry, even if they are
composed of particles with only two-fold symmetry. To understand this effect,
we propose a model for the statistical mechanics of particles with almost
four-fold symmetry, which is weakly broken down to two-fold. We introduce a
coefficient $\kappa$ to characterize the symmetry breaking, and find that the
tetratic phase can still exist even up to a substantial value of $\kappa$.
Through a Landau expansion of the free energy, we calculate the mean-field
phase diagram, which is similar to the result of a previous hard-particle
excluded-volume model. To verify our mean-field calculation, we develop a Monte
Carlo simulation of spins on a triangular lattice. The results of the
simulation agree very well with the Landau theory.

17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
21
The categories of this paper are: adap-org
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol