Why do newer degrees of freedom appear in higher-order truncated hydrodynamic theory?

An exact derivation of relativistic hydrodynamics from an underlying microscopic theory has been shown to be an all-order theory. From the relativistic transport equation of kinetic theory, the full expressions of hydrodynamic viscous fluxes have been derived which turn out to include all orders of...

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Main Author: Sukanya Mitra
Format: Article
Language:English
Published: Elsevier 2025-01-01
Series:Physics Letters B
Online Access:http://www.sciencedirect.com/science/article/pii/S0370269324007329
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author Sukanya Mitra
author_facet Sukanya Mitra
author_sort Sukanya Mitra
collection DOAJ
description An exact derivation of relativistic hydrodynamics from an underlying microscopic theory has been shown to be an all-order theory. From the relativistic transport equation of kinetic theory, the full expressions of hydrodynamic viscous fluxes have been derived which turn out to include all orders of out-of-equilibrium derivative corrections. It has been shown, that for maintaining causality, it is imperative that the temporal derivatives must include all orders, which can be resummed in non-local, relaxation operator-like forms and finally ‘integrated in’ introducing newer degrees of freedom. The theory can of course be truncated at any higher spatial orders, but the power over the infinite temporal sum increases correspondingly such that the causality is respected. As a result, the theory truncated at any higher order of spatial gradient, requires newer degrees of freedom for each increasing order.
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series Physics Letters B
spelling doaj-art-b25ea4be33e148c1a8838a75cccaeb1a2025-01-10T04:37:27ZengElsevierPhysics Letters B0370-26932025-01-01860139174Why do newer degrees of freedom appear in higher-order truncated hydrodynamic theory?Sukanya Mitra0School of Physical Sciences, National Institute of Science Education and Research, An OCC of Homi Bhabha National Institute, Jatni-752050, IndiaAn exact derivation of relativistic hydrodynamics from an underlying microscopic theory has been shown to be an all-order theory. From the relativistic transport equation of kinetic theory, the full expressions of hydrodynamic viscous fluxes have been derived which turn out to include all orders of out-of-equilibrium derivative corrections. It has been shown, that for maintaining causality, it is imperative that the temporal derivatives must include all orders, which can be resummed in non-local, relaxation operator-like forms and finally ‘integrated in’ introducing newer degrees of freedom. The theory can of course be truncated at any higher spatial orders, but the power over the infinite temporal sum increases correspondingly such that the causality is respected. As a result, the theory truncated at any higher order of spatial gradient, requires newer degrees of freedom for each increasing order.http://www.sciencedirect.com/science/article/pii/S0370269324007329
spellingShingle Sukanya Mitra
Why do newer degrees of freedom appear in higher-order truncated hydrodynamic theory?
Physics Letters B
title Why do newer degrees of freedom appear in higher-order truncated hydrodynamic theory?
title_full Why do newer degrees of freedom appear in higher-order truncated hydrodynamic theory?
title_fullStr Why do newer degrees of freedom appear in higher-order truncated hydrodynamic theory?
title_full_unstemmed Why do newer degrees of freedom appear in higher-order truncated hydrodynamic theory?
title_short Why do newer degrees of freedom appear in higher-order truncated hydrodynamic theory?
title_sort why do newer degrees of freedom appear in higher order truncated hydrodynamic theory
url http://www.sciencedirect.com/science/article/pii/S0370269324007329
work_keys_str_mv AT sukanyamitra whydonewerdegreesoffreedomappearinhigherordertruncatedhydrodynamictheory