Nuclear states in strongly coupled quark-gluon plasma from gauge-gravity correspondence

Abstract

In a deconfined phase, quarks, anti-quarks and gluons are not necessary to be in a colorless bound state. They can form various color non-singlet (or exotic for short) nuclear bound states as well as color singlet bound states in the strongly coupled quark-gluon plasma (sQGP) given that baryon number density is sufficiently large. We study the matter of sQGP mainly occupied by these nuclear states via the so-called Sakai-Sugimoto model, which is a gravity dual model of large Nc QCD. Note that Nc denotes the number of colours. We propose the gravity dual models of exotic nuclear states in the deconfining background of the Sakai-Sugimoto model with flavour degrees of freedom turned off. Moreover, we calculate and compare binding energies and screening lengths of these nuclear states as an analysis of their stabilities. The results indicate that these nuclear states are less stable than normal hadrons. Then, turning on the flavour degrees of freedom, we explore the possibilities of the existence of the multiquark matter, which is a thermodynamic phase representing sQGP mainly filled with exotic nuclear states, to be present in a certain region of phase diagram. This matter is found to be more stable thermodynamically than the vacuum and chiral-symmetric quark-gluon plasma phases (χS-QGP) in the region in phase diagram of high chemical potential and low temperature, although it is less stable than the normal nuclear matter. The thermodynamic relations of this matter are also determined. The relations of pressure versus baryon number density are found to be P ∼ d² for small number density, and P ∼ d[superscript 7/5] for large number density. The entropy density is found to be proportional to the temperature as s ∼ T⁵ for the normal nuclear matter, but s ∼ T for the exotic nuclear matter.