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A panoply of Schwinger-Keldysh transport

Kristan Jensen, Raja Marjieh, Natalia Pinzani-Fokeeva, Amos Yarom

SciPost Phys. 5, 053 (2018) · published 27 November 2018


We classify all possible allowed constitutive relations of relativistic fluids in a statistical mechanical limit using the Schwinger-Keldysh effective action for hydrodynamics. We find that microscopic unitarity enforces genuinely new constraints on the allowed transport coefficients that are invisible in the classical hydrodynamic description; they are not implied by the second law or the Onsager relations. We term these conditions Schwinger-Keldysh positivity and provide explicit examples of the various allowed terms.

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