Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The electrical conductivity of a pion gas   The electrical conductivity of a pion gas at low temperatures is studied in
the framework of Linear Response and Chiral Perturbation Theory. The standard
ChPT power counting has to be modified to include pion propagator lines with a
nonzero thermal width in order to properly account for collision effects
typical of Kinetic Theory. With this modification, we discuss the relevant
chiral power counting to be used in the calculation of transport coefficients.
The leading order contribution is found and we show that the dominant higher
order ladder diagrams can be treated as perturbative corrections at low
temperatures. We find that the DC conductivity $\sigma (T)$ is a decreasing
function of $T$, behaving for very low $T$ as $\sigma (T)\sim
e^2m_\pi\sqrt{m_\pi/T}$, consistently with nonrelativistic Kinetic Theory. When
unitarization effects are included, $\sigma(T)$ increases slowly as $T$
approaches the chiral phase transition. We compare with related works and
discuss some physical consequences, especially in the context of the low-energy
hadronic photon spectrum in Relativistic Heavy Ion Collisions.

29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
18
The categories of this paper are: econ
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con