---
abstract: 'The quark matter created in relativistic nuclear collisions is interpreted as a nearly-perfect fluid. The recent efforts to explore its finite-density properties in the beam energy scan programs motivate one to revisit the issue of the local rest frame fixing in off-equilibrium hydrodynamics. I first investigate full second-order relativistic hydrodynamics in the Landau and the Eckart frames. Then numerical hydrodynamic simulations are performed to elucidate the effect of frame choice on flow observables in relativistic nuclear collisions. The results indicate that the flow can differ in the Landau and the Eckart frames but charged particle and net baryon rapidity distributions are mostly frame independent when off-equilibrium kinetic freeze-out is considered.'
author:
- Akihiko Monnai
bibliography:
- 'frame.bib'
title:  Landau and Eckart frames for relativistic fluids in nuclear collisions 
---

Introduction {#sec1}
============

The existence of the strongly-coupled quark-gluon plasma [@Yagi:2005yb] as a high-temperature phase of QCD has been partly motivated by a number of relativistic hydrodynamic analyses of high-energy nuclear collisions at BNL Relativistic Heavy Ion Collider [@Arsene:2004fa; @Back:2004je; @Adams:2005dq; @Adcox:2004mh] and CERN Large Hadron Collider [@Aamodt:2010pa; @ATLAS:2011ah; @Chatrchyan:2012wg]. Modern versions of such analyses incorporate the effects of viscosity to take account of off-equilibrium processes in the system, 