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The Shear Viscosity in an Anisotropic Unitary Fermi Gas
Quantum Gases · Submitted 16 Jul 2016
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim This intuition, along with results from a Boltzmann analysis that we perform, suggests that a violation of the KSS bound can perhaps occur in the unitary Fermi gas system when it is subjected to a suitable anisotropic trapping potential which may be approximated to be linear in a suitable range of parameters.
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The abstract, sentence by sentence
We consider a system consisting of a strongly interacting, ultracold unitary Fermi gas under harmonic confinement. Our analysis suggests the possibility of experimentally studying, in this system, an anisotropic shear viscosity tensor driven by the anisotropy in the trapping potential. In particular, we suggest that this experimental setup could mimic some features of anisotropic geometries that have recently been studied for strongly coupled field theories which have a gravitational dual. Results using the AdS/CFT correspondence in these theories show that in systems with a background linear potential, certain viscosity components can be made much smaller than the entropy density, parametrically violating the bound proposed by Kovtun, Son and Starinets (KSS). This intuition, along with results from a Boltzmann analysis that we perform, suggests that a violation of the KSS bound can perhaps occur in the unitary Fermi gas system when it is subjected to a suitable anisotropic trapping potential which may be approximated to be linear in a suitable range of parameters. We give a concrete proposal for an experimental setup where an anisotropic shear viscosity tensor may arise. In such situations, it may also be possible to observe a reduction in the spin one component of the shear viscosity from its lowest value observed so far in ultracold Fermi gases. In extreme anisotropic situations, the reduction may be enough to reduce the shear viscosity to entropy ratio below the proposed KSS bound, although this regime is difficult to analyze in a theoretically controlled manner.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We consider a system consisting of a strongly interacting, ultracold unitary Fermi gas under harmonic confinement. | background 0.71 | 0.33 | 0.03 | asserted 0.92 |
| s1 | Our analysis suggests the possibility of experimentally studying, in this system, an anisotropic shear viscosity tensor driven by the anisotropy in the trapping potential. | contribution 0.56 | 0.54 | 0.27 | hedged possibility 1.00 |
| s2 | In particular, we suggest that this experimental setup could mimic some features of anisotropic geometries that have recently been studied for strongly coupled field theories which have a gravitational dual. | interpretation 0.56 | 0.13 | 0.06 | hedged possibility 1.00 |
| s3 | Results using the AdS/CFT correspondence in these theories show that in systems with a background linear potential, certain viscosity components can be made much smaller than the entropy density, parametrically violating the bound proposed by Kovtun, Son and Starinets (KSS). | background 0.99 | 0.06 | 0.11 | asserted 0.99 |
| s4 | This intuition, along with results from a Boltzmann analysis that we perform, suggests that a violation of the KSS bound can perhaps occur in the unitary Fermi gas system when it is subjected to a suitable anisotropic trapping potential which may be approximated to be linear in a suitable range of parameters. | interpretation 0.86 | 0.70 | 0.52 | hedged possibility 0.98 |
| s5 | We give a concrete proposal for an experimental setup where an anisotropic shear viscosity tensor may arise. | contribution 0.94 | 0.73 | 0.11 | asserted 0.74 |
| s6 | In such situations, it may also be possible to observe a reduction in the spin one component of the shear viscosity from its lowest value observed so far in ultracold Fermi gases. | interpretation 0.71 | 0.17 | 0.08 | hedged possibility 0.99 |
| s7 | In extreme anisotropic situations, the reduction may be enough to reduce the shear viscosity to entropy ratio below the proposed KSS bound, although this regime is difficult to analyze in a theoretically controlled manner. | limitation 0.91 | 0.17 | 0.39 | hedged possibility 0.98 |
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The paper
Original abstract
We consider a system consisting of a strongly interacting, ultracold unitary Fermi gas under harmonic confinement. Our analysis suggests the possibility of experimentally studying, in this system, an anisotropic shear viscosity tensor driven by the anisotropy in the trapping potential. In particular, we suggest that this experimental setup could mimic some features of anisotropic geometries that have recently been studied for strongly coupled field theories which have a gravitational dual. Results using the AdS/CFT correspondence in these theories show that in systems with a background linear potential, certain viscosity components can be made much smaller than the entropy density, parametrically violating the bound proposed by Kovtun, Son and Starinets (KSS). This intuition, along with results from a Boltzmann analysis that we perform, suggests that a violation of the KSS bound can perhaps occur in the unitary Fermi gas system when it is subjected to a suitable anisotropic trapping potential which may be approximated to be linear in a suitable range of parameters. We give a concrete proposal for an experimental setup where an anisotropic shear viscosity tensor may arise. In such situations, it may also be possible to observe a reduction in the spin one component of the shear viscosity from its lowest value observed so far in ultracold Fermi gases. In extreme anisotropic situations, the reduction may be enough to reduce the shear viscosity to entropy ratio below the proposed KSS bound, although this regime is difficult to analyze in a theoretically controlled manner.
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References
How the literature uses it
9 arXiv papers cite this in 16 sentences
Papers citing it · 11 sentences without a confident label
Uses its data or values 1 paper
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In particular, [equation] where [equation] $𝒢(y)$ can be obtained (see Ref. [ref] for details) by analyzing the thermodynamic measurements carried out in Ref. [ref] .
A Proposal for measuring Anisotropic Shear Viscosity in Unitary Fermi Gases · Introduction · 0.84
Compares with it 1 paper
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The result for a weakly interacting Fermi gas for arbitrary $T/E_F$, is presented in Appendix B of [ref] .
Viscosity for Anisotropic Reissner Nordstr\"om Blackbranes · Comparison with the Boltzmann results · 0.81
Cites it as background 3 papers
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Some other theoretical developments related to the magnetic field in heavy ion collisions includes magneto-vortical evolution [ref] , calculation of Wigner functions for fermions in strong magnetic fields [ref] , shear viscosity in an anisotropic unitary Fermi gas [ref] , the shear and bulk viscosity of Quark-Gluon-Plasma (QGP) in strong magnetic fields [ref] etc.
One particle distribution function and shear viscosity in magnetic field: a relaxation time approach · Introduction · 1.00
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Interestingly, violations of the KSS bound have also been discussed in pure condensed matter models [ref] .
Breaking rotations without violating the KSS viscosity bound · Introduction · 0.82
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In this section we will evaluate the non-conformal $g_s M^2/N$-corrections to the shear viscosity $η$ by considering the EOM for the tensor mode of metric fluctuations up to NLO in $N$, and also estimate the same for the shear viscosity - entropy density ratio $η/s$; see [ref] , [ref] , [ref] , [ref] and [ref] for a summary, higher derivative corrections to and violations of the $η/s=1/4π$-bound.
Application of top-down holographic thermal QCD at finite coupling · NLO Corrections in N to $η$ and $η/s$ · 1.00
What it cites · 4 sentences without a confident label
Cites as background 1 paper
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For $T→0$ the corrections to LDA have been previously studied in Refs. [ref] .
The Unitary Fermi Gas in a Harmonic Trap and its Static Response · Discussion on $κ_LDA$ · 0.91
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