Dynamical Study Of The Tetra-neutron System

The standard model is composed of SU(3) gauge field theory, quantum QCD and SU(2)xU(1) gauge field theory, electroweak unification theory. With the discovery of the"God particle" Higgs by Atlas and CMS Collaborations at LHC in 2012,this theory is being perfected step by step. This model tells us that there are three generations quarks which the masses are generated through the Higgs mechanism, and three generations of leptons and gauge bosons, through which the four types of fundamental interaction emerged. These fundamental particles constitute the hadrons, mesons, nuclei, atoms,molecules and matters, which constitute the whole world. The standard model has been able to describe most of the material structures. In high energy range, many problems can be solved accurately by using the perturbation method of QCD. But in the low energy region, the research of the meson and baryon spectra, hadron-hadron interaction, the non-perturbative nature of QCD prevent the application of the perturbation method. Many attempts are invoked to explore the hadron properties. Quark model, chiral perturbation theory, large Nc expansion, Dyson-Schwinger equation, lattice gauge theory, light-cone QCD, QCD sum rule, etc. are the methods used in the low energy range. Many progresses are achieved. Every method has its advantages and also disadvantages.Few-body system study is a very important. On the one hand, few-body systems exist in the material world, and it is the basic form of material existence, so we must study it.On the other hand, with the increase of the number of particles, the system will get more freedom and complex color structure, the study of few-body systems will enable us to have a deeper understanding of QCD. The phenomenological quark model is an effective method in dealing with the few-quark systems. In this paper, the quark model is used to study the dynamics of the four neutron system. The study of tetra-neutron system began in 1950s. As for its existence, no definite conclusions are obtained. In 2002, Marques et al., claimed that the existence of tetra-neutron, but the latter experiments could not confirm the results. In 2016, Kisamori stated again that the hints of the existence of tetra-neutron was observed. So the theoretical research of tetra-neutron is demanded.The significance of the present work is to explain the experimental discovery and extend the quark model to a wider range of systems to see the validity of quark model. The quark model will be modified and developed according to the results. In addition, this work also enables us to have a further understanding of low energy QCD by studying the properties of the system with more degrees of freedom and more complex color structure.The approach of quark model are successful in describing the properties of hadrons,the hadron-hadron interactions. The model has been extended to the study of tetra-quark, pentaquark and hexaquark systems. In this work, the chiral quark model and quark delocalization color screening model (QDCSM) are employed. First the effective potential between two neutrons are obtained in quark model. the the gaussian expansion method is invoked to study the dynamics of tetra-neutron system. The energy of the system is obtained by solving the Schrodinger equation by using gaussian expansion methods. The bound state appears if the energy of the system lower than the four times of neutron mass. At the same time, the rationality and validity of this method will be shown up by comparing the results with that of the previous research. In addition, we try to obtain a more efficient gaussian expansion method. Finally, compared with the previous work,we have a more comprehensive understanding of the four neutron system. By using the neutron-neutron interaction derived from quark model, our calculations show that the tetra-neutron state is unbound. This result is in agreement with the most calculations on hadron level, but it disagrees with that of the previous work of our group by employing the adiabatic approximation. The further dynamical calculation on quark level is needed to clarify the situation.The structure of this paper is as follows: This paper is divided into five chapters, the first chapter is introduction, which mainly introduces the research history of four neutron system, include the experiment work, the calculation theory. At the end of this chapter,the details work of this paper are introduced. In the second chapter, we introduce the quark model, the 3P0 model and the coupling effect. The third chapter is the core content of this paper. The details of the calculation method are presented. In the fourth chapter,the results are analyzed and discussed, the relevant conclusions are drawn, and a short summary of the work is given and the future work is prospected.