Studies On CFL Color Superconducting Quark Matter And Properties Of Hybrid Stars

Since neutrons were found, scientists have been trying to find theinterior structure and bulk properties of neutron stars. In the core ofneutron stars, hyperons, boson condensations and quark matter may be exist.It is widely accepted that hadronic matter undergoes a phase transitionto strange quark matter at the high density range. The study of quantumchromodynamics (QCD) indicates that quark matter might be in colorsuperconducting phase at quite high density range. It is generally agreedthat the ground state of QCD with three flavors is the color-flavor-locked(CFL) quark phase.In this thesis, using the relativistic mean field theory(RMFT) to describe the hadronic phase and the MIT bag model to describethe CFL quark phase, we study the bulk properties of hybrid stars.Firstly, we discuss neutron stars including hadronic matter and findout stiffer equation of state (EOS) to describe massive neutron stars.Using the RMFT, we discuss the bulk properties of hadronic stars and findthat NLSH parameter set can give the stiffest EOS from the nine parametersets. With the EOS one can obtain the mass-radius relation which can coverthe data of the most massive star J1614-2230（M=(1.97±0.04) M⊙）. Evenif hyperons are included, the maximum mass of the neutron star still isin the range of the data of J1614-2230. Secondly, we discuss pure CFL strange quark stars and investigate theconditions that can give rise to massive CFL quark stars. In the MIT bagmodel, we investigate the influence which the change of the energy gap,strange current quark mass and bag constant on the structure andproperties of CFL strange quark stars. The results show that the energygap and the bag constant have the significant effects on CFL quark stars,but the effect of strange current quark mass is quite small. From theresult we find that the role of the bag constant and the CFL energy gapare opposite. We want to get J1614-2230massive mass pure CFL quark stars,we should reduce the bag constant under the definite energy gap or increasethe energy gap under the definite bag constant. From this, one can concludethat as long as there is strong interaction between quarks (e.g. Colorsuperconductivity) rather than freedom, the massive CFL quark stars ispossible. This conclusion is consistent with the literature [Demo10].Thirdly, we discuss structure of hybrid star with the mixed hadron+CFLquark phase, we first discuss the conditions producting hybrid star withmixed hadron+CFL quark phase. At the core of Neutron stars, with theincrease of desities the phase transition from nuclear matter to CFL colorsuperconducting quark matter can occur. When the surface tension and theCoulomb interaction are ignored, we can build a mixed phase betweenhadronic matter and CFL color superconducting quark matter, and discussthe structural characteristics of hybrid stars with the mixed phase.In2010, Demorest et al found the heaviest neutron star[Demo10], whichpresent a new limit for determining the equation of state of dense matter.Using the NLSH EOS and the MIT bag model, we investigate hybrid stars withthe CFL quark core in the new mass limitation from PSR J1614-2230. Weinvestigate the influence of the change of the energy gap on structureand properties of the hybrid stars with mixed hadron+CFL quark phase cores,we find interesting results.There exist three regions when the energy gap increases from0to200MeV.they are as follows:(i) hybrid stars regionwith mixed hadron+CFL quark phase.(△=0～100MeV).In this range thenetron stars are hybrid stars which are very close to hadron stars.(ii)pure CFL Color superconductivity quark star region (△=150MeV～200MeV).In this range the netron stars are pure CFL quark stars.(iii) intermediatetransition region(△=100MeV～150MeV). In this range, the hybrid starsshow a transition behavior from hadron stars to CFL quark stars. At thesame time, using our parameters we find the massive mass hybrid stars inthe range of△＜40MeV, whose masses and radii are in the data range ofpulsar J1614-2230.Fanally, we investigate the appearance of the third family of compactstars with the CFL quark cores. Almost40years ago, Gerlach found thata third family of stable configurations of compact stars could exist innature besides two families of white dwarfs and neutron stars. He foundthat it was due to a large discontinuity behavior in the speed of sound(dp/dε) of the corresponding EoS. Glendenning et al also found that thepractical physical mechanism was a phase transition from hadronic to quarkmatter. We build a mixed phase between hadronic matter and CFL colorsuperconducting quark matter. We calculate EOS of hybrid stars with mixedhadron+CFL quark phase, and find that the speed of sound (dp/dε) of thecorresponding EoS is discontinuity, this expresses that a third familyof compact stars might appear.It should be emphasized that we find thethird family of hybrid stars with the CFL quark core in the wide rangeof the CFL energy gap (100MeV≤△＜150MeV). In the early investigatation,among200mass-radius trlations the only third family of hybrid stars withthe normal quark core was found by using the TM2EOS in the narrow parameterrange（176MeV≤B1/4≤182MeV）, By comparison with the early investigation,we find that the greatest possible third family may be the hybrid stars with the CFL quark core.In addition，in our calculation, neutron star twinsalways exist in certain region, and they are treated as a signature forthe existence of a third family. The existence of the third family maybe equivalent to the existence of the phase transition from hadronic phaseto the CFL quark phase.