Equation of state at high densities and modern compact star observations

TL;DR

Recent high-precision observations of neutron stars with high mass and large radii challenge soft equations of state, but modern quantum field theories including color superconductivity can describe hybrid stars consistent with these constraints.

Contribution

The paper demonstrates that advanced quantum field theoretical models, incorporating color superconductivity and vector mean fields, can produce stiff hybrid equations of state compatible with recent observations.

Findings

Hybrid star models with color superconductivity satisfy observational constraints.

Deconfinement transition is weakly first order, affecting transport properties.

Implications for future nucleus-nucleus collision experiments at high baryon densities.

Abstract

Recently, observations of compact stars have provided new data of high accuracy which put strong constraints on the high-density behaviour of the equation of state of strongly interacting matter otherwise not accessible in terrestrial laboratories. The evidence for neutron stars with high mass (M =2.1 +/- 0.2 M_sun for PSR J0751+1807) and large radii (R > 12 km for RX J1856-3754) rules out soft equations of state and has provoked a debate whether the occurence of quark matter in compact stars can be excluded as well. In this contribution it is shown that modern quantum field theoretical approaches to quark matter including color superconductivity and a vector meanfield allow a microscopic description of hybrid stars which fulfill the new, strong constraints. The deconfinement transition in the resulting stiff hybrid equation of state is weakly first order so that signals of it have to be expected due to specific changes in transport properties governing the rotational and cooling evolution caused by the color superconductivity of quark matter. A similar conclusion holds for the investigation of quark deconfinement in future generations of nucleus-nucleus collision experiments at low temperatures and high baryon densities such as CBM @ FAIR.