Constraining and applying a generic high-density equation of state

Abstract

We discuss the "constant speed of sound" (CSS) parameterization of the equation of state of high density matter and its application to the Field Correlator Method (FCM) model of quark matter. We show how observational constraints on the maximum mass and typical radius of neutron stars are expressed as constraints on the CSS parameters. We find that the observation of a 2 M star already severely constrains the CSS parameters, and is particularly difficult to accommodate if the squared speed of sound in the high density phase is assumed to be around 1/3 or less.We show that the FCM equation of state can be accurately represented by the CSS parameterization, which assumes a sharp transition to a high-density phase with density-independent speed of sound. We display the mapping between the FCM and CSS parameters, and see that FCM only allows equations of state in a restricted subspace of the CSS parameters.

Towards generating a new supernova equation of state: A systematic analysis of cold hybrid stars

“…In this paper, c 2 QM ¼ 1=3 is used, which is typical for many quark EOSs and also in agreement with other, more sophisticated models (e.g., [16,47]). …”

“…For the hadronic EOS, they used the relativistic mean-field model DD2 [13] as we do in the present study. Alford's classification was also applied in a number of other works [14][15][16][17], varying the hadronic and/or quark EOSs. Similar parameter scans for quark matter properties were done in [18,19], where, however, only the maximum mass but not the type of hybrid star was investigated.…”

QCD equation of state and cosmological parameters in the early universe

“…The FCM has been extended to finite temperature and chemical potential [17][18][19] and the analytical results, in the gaussian approximation, are in good agreement with the lattice data on thermodynamic quantities, (available for small µ B only). Moreover, the application of the FCM for large values of the chemical potential allows to obtain a simple expression of the Equation of State of the quark-gluon matter in the range of the baryon density relevant for the study of neutron stars [25,26,28]. magnetic field, B, has been included in the FCM equation of state [20,21] and the quark (q) pressure and the gluon (g) pressure turn out to be…”

Strange Quark Stars in Binaries: Formation Rates, Mergers, and Explosive Phenomena

“…Very small radii for stars having masses of about 1.4 -1.5 M are obtained only if the equation of state of dense matter is very soft at densities of about 2 -3 times nuclear matter saturation density. On the other hand, so soft equations of state lead to maximum masses significantly smaller than 2 M , because to reach very large masses would imply an extreme stiffening of the equation of state at larger densities, saturating the limit of causality, a situation that is not very realistic (Alford et al 2015). If future observations with new facilities, such as the NICER experiment on-board ISS (Gendreau et al 2012), will confirm the existence of very compact stars, then one has to explain how the equation of state of dense matter could be at the same time very soft (to explain the very compact configurations) and very stiff (to explain the very massive configurations).…”

“…It is clear indeed that the center of this stellar object could be the site of the most dense form of nuclear matter we are aware of: depending on the adopted model for the equation of state, the central density of this star could be larger than about 3 times the nuclear saturation density. There are many different ideas on the composition of matter at such a high density: for instance, hyperons (Chatterjee & Vidaña 2016) or delta resonances (Drago et al 2014b) could form, or a phase transition to quark matter could occur (Alford et al 2015). The need to fulfill the two solar mass limit provides tight microphysical constraints on those scenarios.…”