Specific viscosity of neutron-rich nuclear matter from a relaxation time approach

Abstract

The specific viscosity of neutron-rich nuclear matter is studied from the relaxation time approach using an isospin-and momentum-dependent interaction and the nucleon-nucleon cross sections taken as those from the experimental data modified by the in-medium effective masses as used in the IBUU transport model calculations. The relaxation time of neutrons is larger while that of protons is smaller in neutron-rich nuclear matter compared with that in symmetric nuclear matter, and this leads to a larger specific viscosity in neutron-rich nuclear matter. In addition, the specific viscosity decreases with increasing temperature because of more frequent collisions and weaker Pauli blocking effect at higher temperatures. At lower temperatures the specific viscosity increases with increasing density due to the Pauli blocking effect, while at higher temperatures it slightly decreases with increasing density as a result of smaller in-medium effective masses at higher densities.

Isospin splitting of nucleon effective mass and shear viscosity of nuclear matter

“…Similar to the behavior near hadron-quark phase transition, the η/s also shows a minimum in the vicinity of nuclear liquid-gas phase transition from various approaches [11][12][13][14][15][16]. Since the correlation between the elliptic flow and the specific shear viscosity seems to be a general feature in not only relativistic [3] but also intermediate-energy heavy-ion collisions [17], it might be promising to measure the η/s experimentally, meanwhile providing an alternative way of searching for nuclear liquid-gas phase transition in heavy-ion collisions at intermediate energies in the future.In my previous studies, the specific shear viscosity of neutron-rich matter was investigated based on an isospinand momentum-dependent interaction [9,16]. Recently, this interaction has been further improved [18], providing the possibility of studying more flexibly detailed isovector properties of nucleon interaction, such as the neutron-proton effective mass splitting.…”

“…In my previous studies, the specific shear viscosity of neutron-rich matter was investigated based on an isospinand momentum-dependent interaction [9,16]. Recently, this interaction has been further improved [18], providing the possibility of studying more flexibly detailed isovector properties of nucleon interaction, such as the neutron-proton effective mass splitting.…”

“…The quark-gluon plasma (QGP) produced in ultrarelativistic heavy-ion collisions is believed to be a nearly ideal fluid and has a very small specific shear viscosity η/s [1][2][3][4], i.e., the ratio of the shear viscosity η to the entropy density s. It has been further found that the η/s decreases with increasing temperature in the hadronic phase while increases with increasing temperature in QGP, resulting in a minimum value at the temperature of hadron-quark phase transition [5,6]. At even lower temperatures, the η/s of nuclear matter with nucleon degree of freedom has been investigated from the relaxation time approach [7][8][9] and transport model studies [10][11][12][13]. Similar to the behavior near hadron-quark phase transition, the η/s also shows a minimum in the vicinity of nuclear liquid-gas phase transition from various approaches [11][12][13][14][15][16].…”

“…The shear viscosity is calculated by assuming that in the uniform nuclear system there exists a static flow field in the z direction with flow gradient in the x direction. The shear force, which is related to the nucleon flux as well as the momentum exchange between flow layers, is proportional to the flow gradient, and the proportionality coefficient, i.e., the shear viscosity, turns out to be [9] …”

“…I now briefly review the main ingredient of the relaxation time approach used in previous studies [9,16]. The shear viscosity is calculated by assuming that in the uniform nuclear system there exists a static flow field in the z direction with flow gradient in the x direction.…”