Narrow Results

We describe work being done at Baylor University investigating the possibility of new states of mesonic matter containing two or more quark–antiquark pairs. To put things in context, we begin by describing the lattice approach to hadronic physics. We point out there is a need for a quark model which can give an overall view of the quark interaction landscape. A new application of the Thomas–Fermi (TF) statistical quark model is described, similar to a previous application to baryons. The main usefulness of this model will be to detect systematic energy trends in the composition of the various particles. It could be a key to identifying families of bound states, rather than individual cases. Numerical results based upon a set of parameters derived from a phenomenological model of tetraquarks are given.

In this chapter, we investigate the structure and composition of hot neutron star matter and proto-neutron stars. Such objects are made of baryonic matter that is several times denser than atomic nuclei and tens of thousands of times hotter than the matter in the core of our Sun. The relativistic finite-temperature Green function formalism is used to formulate the expressions that determine the properties of such matter in the framework of the density-dependent mean-field approach. Three different sets of nuclear parameterizations are used to solve the many-body equations and to determine the models for the equation of state of ultra-hot and dense stellar matter. The meson–baryon coupling schemes and the role of the Δ(1232) baryon in proto-neutron star matter are discussed in great detail. The use of the non-local three-flavor Nambu–Jona-Lasinio model to describe quark matter, the hadron-quark composition of dense baryonic matter at zero temperature is discussed. General relativistic models of non-rotating as well as rotating proto-neutron stars are presented in part two of our study.

The Bodmer-Terazawa-Witten hypothesis of absolutely stable quark matter made of up, down, and strange quarks ((u,d,s) matter) is of much astrophysical and fundamental interest. One consequence is a large binding energy release associated with the conversion of a neutron star to a quark star. A quantitative understanding of the dynamic aspect of the conversion is necessary in order to find out whether this energy is released quietly or in an explosive manner. We address numerically (i.e. solving the reaction-diffusion-advection equations for (u,d) to (u,d,s) combustion) the dynamic processes through which the conversion appears. We find fundamentally very different results from semi-analytic calculations, with front speeds that are several orders of magnitude higher for the former. Resolving the hadronic-quark-matter interface is necessary, since approximations like Coll’s condition may quench the burning, while properly resolving the flame can make combustion always thermodynamically favourable if the hypothesis of absolutely stable strange quark matter is true. We find that lepton physics, including weak decays, electron equation-of-state (EoS), neutrino EoS, and neutrino transport are at the very least as important to the physics of the burning front as the EoS of highly dense matter. In concert, these effects induce novel wrinkling instabilities (such as the deleptonization instability) possibly leading to a deflagration-detonation and/or a quark-core collapse Quark-Nova.

We discuss the temporal structure of the Gamma-Ray-Bursts (GRBs) light curves and we analyse the occurrence of quiescent times which are long periods within the prompt emission in which the inner engine is not active. We show that if a long quiescent time is present, it is possible to divide the total duration of GRBs into three periods: the pre-quiescence emission, the quiescent time and the post-quiescence emission. We then discuss a model of the GRBs inner engine based on the formation of quark phases during the life of an hadronic star. Within this model the pre-quiescence emission is interpreted as due to the deconfinement of quark inside an hadronic star and the formation of 2SC quark matter or unpaired quark matter (UQM). The post-quiescence emission is due to the conversion of 2SC (or UQM) into the Color-Flavor-Locking (CFL) phase. The temporal delay between these two processes is connected with the nucleation time of the CFL phase in the 2SC (UQM) phase and it can be associated with the observed quiescent times in the GRBs light curves.

We argue that there is a unique transition state of moderate density between the nuclear matter and superconducting quark matter alternatives. The distinguishing features of this state are discussed.

A possibility and properties of spontaneous magnetization in quark matter are investigated. Magnetic susceptibility is evaluated within Fermi liquid theory, taking into account of screening effect of gluons. Spin wave in the polarized quark matter, as the Nambu-Goldstone mode, is formulated by way of the coherent-state path integral.

We investigate the properties of the hadron-quark mixed phase in compact stars using a Brueckner-Hartree-Fock framework for hadronic matter and the MIT bag model for quark matter. We find that the equation of state of the mixed phase is similar to that given by the Maxwell construction. The composition of the mixed phase, however, is very different from that of the Maxwell construction; in particular, hyperons are completely suppressed.

The influence of intense magnetic fields on the phase structure of cold quark matter is investigated using some extended versions of the SU(2)_f NJL model. We consider first one that includes general flavor mixing and vector interactions. Charge neutrality and beta equilibrium effects, which are relevant to the study of compact stars are taken into account for this case. Finally, superconducting quark matter is also studied through the introduction of diquark pairing interactions.

Depending on the density reached in the cores of neutron stars, such objects may contain stable phases of novel matter found nowhere else in the Universe. This article gives a brief overview of these phases of matter and discusses astrophysical constraints on the high-density equation of state associated with ultra-dense nuclear matter.

In this work we focus our study on the transition from hadron to deconfined quark matter, and we shall assume the phase transition is a first-order with two independent components, which are related to the local conservation of baryon number and the global conservation of electric charge. In this study, two different relativistic effective theories are employed to describe respectively the hadron and quark phases, a model with derivative couplings and an extension of the MIT bag model. We then carry out an analysis of the model parameters and the different hyperon-coupling schemes adopted in order to identify their possible influence on the phase transition.

This lecture presents an overview of the status of the investigation of the properties of the quark-gluon plasma using relativistic heavy ion collisions at the Rleativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). It focuses on the insights that have been obtained by the comparison between experimental data and theoretical calculations.

The possibility of observationally discriminating between various types of neutron stars, described by different equations of state of the nuclear matter, as well as differentiating neutron stars from other types of exotic objects, like, for example, quark stars, is one of the fundamental problems in contemporary astrophysics. We consider the possibility that different types of quark stars, in both normal and superconducting CFL (Color-Flavor-Locked) phase can be differentiated among themselves, and from neutron stars, by the study of the emission properties of the accretion disks. Particular signatures appear in the electromagnetic spectrum, thus leading to the possibility of directly testing the equation of state of the dense matter by using astrophysical observations of the spectra of the accretion disks.

The equation of state (EoS) of dense nuclear matter plays an important role in the structure of pulsar-like objects and the binary compact-star mergers, among various astrophysical phenomena related to neutron stars. Determining the correct EoS (or pressure-density relationship) that describes the inner structure of neutron stars is a fundamental problem of nuclear physics, particle physics, and astrophysics, helping us understand the fundamental constituents of matter and their interactions under extreme conditions. In this chapter, we will review the recent progress on the EoS from both points of view of nuclear physics and astronomy. The current and upcoming multi-messenger observatories will continue improving the detection of pulsars together with the precise measurements of their global and dynamic properties. Laboratory experiments will provide an emerging understanding of nuclear matter EoS and the transition to exotic matter. The long-standing, open problem of the EoS may be understood in the near future through the confrontation of theoretical calculations with laboratory measurements of nuclear properties & reactions and increasingly accurate observations in astronomy.