Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gradient expansion approach to multiple-band Fermi liquids   Promoted by the recent progress of Berry phase physics in spin
galvanomagnetic communities, we develop a systematic derivation of the reduced
Keldysh equation (RKE) which captures the low-energy dynamics of
quasi-particles constrained within doubly degenerate bands forming a single
Fermi surface. Specifically, we project out the fully occupied/empty band
degrees of freedom perturbatively in the gradient expansion, whose coupling
constant measures how a system is disequilibrated. As for the electron-electron
interactions, however, we only employ the so-called adiabatic assumption of the
Fermi liquid theory, so that the effect of electron correlations onto the
adiabatic transport of quasi-particles, i.e. the hermitian (real) part of the
self-energy, is taken into account in an unbiased manner.

10
The categories of this paper are: q-bio
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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
18
The categories of this paper are: econ
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
29
The categories of this paper are: funct-an
6
The categories of this paper are: astro-ph