Longitudinal dynamics from hydrodynamics with an order parameter *

Abstract

Abstract We studied coupled dynamics of hydrodynamic fields and order parameter in the presence of nontrivial longitudinal flow using the chiral fluid dynamics model. We found that longitudinal expansion provides an effective relaxation for the order parameter, which equilibrates in an oscillatory fashion. Similar oscillations are also visible in hydrodynamic degrees of freedom through coupled dynamics. The oscillations are reduced when dissipation is present. We also found that the quark density, which initially peaked at the boundary of the boost invariant region, evolves toward forward rapidity with the peak velocity correlated with the velocity of longitudinal expansion. The peak broadens during this evolution. The corresponding chemical potential rises due to simultaneous decrease of density and temperature. We compared the cases with and without dissipation for the order parameter and also the standard hydrodynamics without order parameter. We found that the corresponding effects on temperature and chemical potential can be understood from the conservation laws and different speeds of equilibration of the order parameter in the three cases.