Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Production of a sterile species: quantum kinetics   Production of a sterile species is studied within an effective model of
active-sterile neutrino mixing in a medium in thermal equilibrium. The quantum
kinetic equations for the distribution functions and coherences are obtained
from two independent methods: the effective action and the quantum master
equation. The decoherence time scale for active-sterile oscillations is
$\tau_{dec} = 2/\Gamma_{aa}$, but the evolution of the distribution functions
is determined by the two different time scales associated with the damping
rates of the quasiparticle modes in the medium: $\Gamma_1=\Gamma_{aa}\cos^2\tm
; \Gamma_2=\Gamma_{aa}\sin^2\tm$ where $\Gamma_{aa}$ is the interaction rate of
the active species in absence of mixing and $\tm$ the mixing angle in the
medium. These two time scales are widely different away from MSW resonances and
preclude the kinetic description of active-sterile production in terms of a
simple rate equation. We give the complete set of quantum kinetic equations for
the active and sterile populations and coherences and discuss in detail the
various approximations. A generalization of the active-sterile transition
probability \emph{in a medium} is provided via the quantum master equation. We
derive explicitly the usual quantum kinetic equations in terms of the
``polarization vector'' and show their equivalence to those obtained from the
quantum master equation and effective action.

27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
30
The categories of this paper are: q-alg
7
The categories of this paper are: hep-th
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio