Quark structure

The discovery of the quark structure of matter led to the suggestion of possible existence of quark stars, which are even more compact than neutron stars. In the presence of indefiniteness concerning the quark structure of matter it is not possible now to make definite statements about the existence or nonexistence of stable quark stars, observational and theoretical investigations on this topic are still in progress. 

Properties of nucleons (p, n). Quark structure symbol, electric charge (e), spin (A) and its direction. There are three valence quarks both in p and n, such that they are colorless... 

The weak interactions change quark and lepton flavors, e.g., a d-quark into -quark or a muon into an electron (this latter, e.g., in the p e Vet /i process). The quark structures of the proton and neutron as well as the properties of nucleons are presented in O Table 2.3. The baryons are built up from three (valence) quarks and massless gluons, but they contain also dynamical (or sea) quarks (quark-antiquark pairs) in a small quantity. The mesons are built up from quark-antiquark pairs and gluons. 

Sooner or later, changes in scientific subjects start to affect the school science curriculum. In the case of biology, it has been sooner rather than later DNA is, at 50 years of age, already firmly part of school biology. In physics, change is patchy, often later rather than sooner. Some glamorous parts of astronomy are present, if only as an option so are simplified accounts of the quark structure of nucleons and mesons. But, with rare exceptions, the revolution introduced by quantum field theory remains unremarked so indeed in large measure do Maxwell s equations, and relativity, aneient ftiough both are. 

Aguirre, R. M., De Paoli, A. L. (2002). Neutron star structure in a quark model with excluded volume correction. Phys.Rev.C68 055804. 

NEUTRON STAR STRUCTURE WITH HYPERONS AND QUARKS... 

Neutron Star Structure with Hyperons and Quarks... 

We first review briefly the description of the bulk properties of uniform quark matter, deconfined from the /3-stable hadronic matter mentioned in the previous section, by using the MIT bag model [31]. The thermodynamic potential of f = u,d,s quarks can be expressed as a sum of the kinetic term and the one-gluon-exchange term [32, 33] proportional to the QCD fine structure... 

The final result for the structure of hybrid neutron stars is shown in Fig. 11, displaying mass-radius and mass-central density relations. It is evident that the most striking effect of the inclusion of quark matter is the increase of the maximum mass, now reaching about 1.5 M . At the same time, the typical neutron star radius is reduced by about 3 km to typically 9 km. Hybrid neutron stars are thus more compact than purely hadronic ones and their central energy density is larger. For completeness, the figure shows besides static neutron star... 

In this contribution we reported the theoretical description of nuclear matter in the BHF approach and its various refinements, with the application to neutron star structure calculation. We pointed out the important role of TBF at high density, which is, however, strongly compensated by the inclusion of hyperons. The resulting hadronic neutron star configurations have maximum masses of only about 1.3 M , and the presence of quark matter inside the star is required in order to reach larger values. 

Abstract We investigate the phase structure of color superconducting quark matter at intermediate densities for two- and three flavor systems. We thereby focus our attention on the influence of charge neutrality conditions as well as /3-equilibrium on the different phases. These constraints are relevant in the context of quark matter at the interior of compact stars. We analyze the implications of color superconductivity on compact star configurations using different hadronic and quark equations of state. 

Figure 7. At / = 0.75, pressure as a function of/./ = / e / > and for the normal and color superconducting quark phases. The dark solid lines represent two locally neutral phases (i) the neutral normal quark phase on the left, and (ii) the neutral gapless 2SC phase on the right. The appearance of the swallowtail structure is related to the first order type of the phase transition in quark matter.

It is interesting to notice that the three pressure surfaces in Figure 7 form a characteristic swallowtail structure. As one could see, the appearance of this structure is directly related to the fact that the phase transition between color superconducting and normal quark matter, which is driven by changing parameter //,. is of first order. In fact, one should expect the appearance of a similar swallowtail structure also in a self-consistent description of the hadron-quark phase transition. Such a description, however, is not available yet. 

The structure of the gap function (33) is then inspired by a physical consideration of a quark pair as in the usual BCS theory we consider here the quark pair on each Fermi surface with opposite momenta, p and —p so that they result in a linear combination of Jn = 0, 1 (see Fig. 3). 4... 

Besides the crust and the hadron shell, the hybrid star contains also a quark core. Both the nucleon shell and the quark core can be in superconducting phases, in dependence on the value of the temperature. Fluctuations affect transport coefficients, specific heat, emissivity, masses of low-lying excitations and respectively electromagnetic properties of the star, like electroconductivity and magnetic field structure, e.g., renormalizing critical values of the magnetic field (/ ,, Hc, Hc2). 

Keywords Relativistic stars - structure and stability, Quark-gluon plasma, Nuclear physics... 

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