QCD in the cores of neutron stars

Abstract

I discuss why state-of-the art perturbative QCD calculations of the equation of state at large chemical potential that are reliable at asymptotically high densities constrain the same equation of state at neutron-star densities. I describe how these theoretical calculations affect the EOS at lower density. I argue that the ab-initio calculations in QCD offer significant information about the equation of state of the neutron-star matter, which is complementary to the current astrophysical observations.

Pseudo-Conformal Sound Speed in the Core of Compact Stars

“…It was therefore referred to-in the absence of a better terminology-as "pseudo-conformal." In this article, we explain how this surprising prediction could account for the possible presence of "deconfined quarks" in the core of compact stars updating recent developments confronting microscopic approaches anchored on QCD proper being discussed in the current literature [3][4][5][6]. It turns out that the notion of pseudo-conformality can figure equally importantly in nuclear physics at low density.…”

“…Some of the results obtained thus far appear to be quite relevant to what we obtained in GnEFT. Among them are the results of the pQCD calculation given in [6] that render feasible even a semi-quantitative comparison with the GnEFT prediction.…”

“…n 1/2 = 4n 0 seems to be ruled out as the sound speed violates the unitarity bound v 2 s /c 2 = 1. Right panel: The state-of-the-art pQCD calculation obtained in [6] indicating the effect of QCD. Note that the central density involved is ∼6n 0 in both cases.…”

“…In Figure 4 (right panel) is plotted the pQCD result of [6]. Here, one sees the way the QCD asymptotically high-density calculations are propagated down to lower densities subjected to "thermodynamic consistency, stability and causality."…”

Repulsive vector interaction as a trigger for the non-conformal peak in $V_s^2$

“…This happens because the model generates a peak in V 2 s at lower densities by stiffening the EoS before the softening, at intermediate densities, forces convergence towards the pQCD predictions. Moreover, a recent study shows that QCD predicts the softening of the EoS in most massive NSs [54]. In a crude application to the description of non-strange quark stars the model predicts a smaller maximum mass-radius ratio than the cases where G V = 0 and G V = G S /3.…”