Cold quark matter with heavy quarks and the stability of charm stars

Abstract

We study the effects of heavy quarks on the equation of state for cold and dense quark matter obtained from perturbative QCD, yielding observables parametrized only by the renormalization scale. We investigate the behavior of charm quark matter under the constraints of β-equilibrium and electric charge neutrality in a region of densities where perturbative QCD is in principle much more reliable. We also analyze the stability of charm stars, and find that such quark stars are unstable under radial oscillations.

Charged charm stars

“…The results derived above indicate that equilibrum condition ∂M/∂ c > 0 is also satisfied by charged charm stars. As discussed in previous studies [13,14], such condition is necessary but not sufficient to determine the stability of charm stars. In order to establish the stability, it is fundamental to analyze the behaviour of the radial oscillation modes.…”

“…Since the proposition that the ground state of strong interacting matter should be described in terms of quarks degrees of freedom [2,3], many studies suggested that the densest observed neutron stars could actually be quark stars [4,5]. Although the most known form of quark star is the one that contains roughly the same numbers of up, down and strange quarks, the so-called strange star [6][7][8][9][10][11], other forms of quark stars have been investigated [12][13][14]. Quark stars containing only up and down quarks were not expected to exist, but recent studies suggest that the stability of dense quark matter in bulk is model dependent, implying that quark matter may not be strange [15].…”

“…In the quark star scenario, charm stars present themselves as a last possibility because bottom and top quarks are too heavy to constitute any stable configuration [4]. Electrically neutral charm stars were previously investigated by Kettner and collaborators [13] in the MIT bag model framework and more recently by Jiménez and Fraga [14] using an approach based on dense and cold perturbative Quantum Chromodynamics (pQCD). One of our goals is to expand these previous studies for the case of charged charm stars.…”

“…The results presented in Refs. [13,14] pointed out that neutral charm stars are unstable against radial oscillations. One important open question is if such conclusion is also valid for the charged case.…”