Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Bulk and shear viscosities of the 2D electron liquid in a doped graphene
  sheet   Hydrodynamic flow occurs in an electron liquid when the mean free path for
electron-electron collisions is the shortest length scale in the problem. In
this regime, transport is described by the Navier-Stokes equation, which
contains two fundamental parameters, the bulk and shear viscosities. In this
Article we present extensive results for these transport coefficients in the
case of the two-dimensional massless Dirac fermion liquid in a doped graphene
sheet. Our approach relies on microscopic calculations of the viscosities up to
second order in the strength of electron-electron interactions and in the
high-frequency limit, where perturbation theory is applicable. We then use
simple interpolation formulae that allow to reach the low-frequency
hydrodynamic regime where perturbation theory is no longer directly applicable.
The key ingredient for the interpolation formulae is the "viscosity transport
time" $\tau_{\rm v}$, which we calculate in this Article. The transverse nature
of the excitations contributing to $\tau_{\rm v}$ leads to the suppression of
scattering events with small momentum transfer, which are inherently
longitudinal. Therefore, contrary to the quasiparticle lifetime, which goes as
$-1/[T^2 \ln(T/T_{\rm F})]$, in the low temperature limit we find $\tau_{\rm v}
\sim 1/T^2$.

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The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
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The categories of this paper are: chem-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-bio
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The categories of this paper are: patt-sol
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The categories of this paper are: solv-int
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The categories of this paper are: astro-ph
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The categories of this paper are: nlin