Specific shear viscosity in hot rotating systems of paired fermions

TL;DR

This paper calculates the specific shear viscosity of rotating nucleon systems considering thermal fluctuations and pair vibrations, revealing how viscosity varies with angular momentum, temperature, and system size.

Contribution

It introduces a comprehensive model including thermal fluctuations and pair vibrations to evaluate shear viscosity in rotating fermionic systems, extending previous approaches.

Findings

Viscosity increases with angular momentum at fixed temperature.

In medium/heavy systems, viscosity decreases with temperature above 2 MeV.

In light systems, viscosity increases with temperature near maximum angular momentum.

Abstract

The specific shear viscosity $\bar\eta$ of a classically rotating system of nucleons that interact via a monopole pairing interaction is calculated including the effects of thermal fluctuations and coupling to pair vibrations within the selfconsistent quasiparticle random-phase approximation. It is found that $\bar\eta$ increases with angular momentum $M$ at a given temperature $T$. In medium and heavy systems, $\bar\eta$ decreases with increasing $T$ at $T\geq$ 2 MeV and this feature is not affected much by angular momentum. But in lighter systems (with the mass number $A\leq$ 20), $\bar\eta$ increases with $T$ at a value of $M$ close to the maximal value $M_{max}$, which is defined as the limiting angular momentum for each system. The values of $\bar\eta$ obtained within the schematic model as well as for systems with realistic single-particle energies are always larger than the universal lower-bound conjecture $\hbar/(4\pi k_B)$ up to $T$=5 MeV.