Shear viscosity and the nucleation of antikaon condensed matter in protoneutron stars

TL;DR

This paper investigates shear viscosities in protoneutron star matter, highlighting the dominant role of neutrinos, and examines how neutrino shear viscosity influences the thermal nucleation rate of antikaon condensed matter, suggesting earlier estimates may be overestimated.

Contribution

It provides the first detailed calculation of neutrino shear viscosity effects on the nucleation of antikaon condensed matter in protoneutron stars.

Findings

Neutrino shear viscosity is significantly higher than that of other species.

Neutrino shear viscosity greatly enhances the nucleation rate prefactor.

Thermal nucleation of antikaon droplets can occur before neutrino diffusion.

Abstract

We study shear viscosities of different species in hot and neutrino-trapped dense matter relevant to protoneutron stars. It is found that the shear viscosities of neutrons, protons and electrons in neutrino-trapped matter are of the same orders of magnitude as the corresponding shear viscosities in neutrino-free matter. Above all, the shear viscosity due to neutrinos is higher by several orders of magnitude than that of other species in neutrino-trapped matter. Next we investigate the effect of shear viscosity in particular, neutrino shear viscosity on the thermal nucleation rate of droplets of antikaon condensed matter in protoneutron stars. The first-order phase transition from hadronic matter to antikaon condensed matter is driven by the thermal nucleation process. We compute the equation of state used for the calculation of shear viscosity and thermal nucleation time within the relativistic mean field model. Neutrino shear viscosity enhances the prefactor in the nucleation rate by several orders of magnitude compared with the $T^4$ approximation of earlier calculations. Consequently the thermal nucleation time in the $T^4$ approximation overestimates our result. Furthermore, the thermal nucleation of an antikaon droplet might be possible in neutrino-trapped matter before neutrino diffusion takes place.