Vanishing bulk viscosities and conformal invariance of the unitary fermi gas.
By requiring general-coordinate and conformal invariance of the hydrodynamic equations, we show that the unitary Fermi gas has zero bulk viscosity, zeta=0, in the normal phase. In the superfluid phase, two of the bulk viscosities have to vanish, zeta1=zeta2=0, while the third one zeta3 is allowed to be nonzero.
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Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195-1550, USA.