Investigation Of Medium Effects For Strongly Interacting Matter Under Extreme Environment

There are two frameworks the finite temperature theory and the kinetic theory for V studying the medium effects of strongly interacting matter. The semi-classical kinetic theory and the imaginary time formal finite temperature field theory are used to study the medium effects of Quark-Gluon Plasma(QGP) and the spectral function of p meson under the hot/dense hadronic environment, respectively. There are more collective effects (for example, Debye screening, quasi-particle exci- tations, etc.) in QGP than in QED plasma. In particular, as strongly interacting mat- ter, the characteristic of QGP is non-Abelian and nonlinear due to the self-interaction of color field. Based on the semi-classical kinetic theory, the nonlinear medium effects of QGP are analyzed. The derivative expansion method is used to iterate the nonlinear kinetic equations of QGP. In the iterating process the spatial derivative is iterated as well. For the first time the nonlinear spatial damping rate has been obtained for the pure gluon plasma in the long wavelength limit on the HTL抯 level. One of the important quantities describing the medium property of QGP is color permittivity. Many properties of medium, such as the dispersion relation and non- linear Landau damping, are closely related with this characteristic quantity. Taking into account the contribution of color field self-interaction, by decomposing the quan- tities in the equations into regular and fluctuation parts, then iterating the fluctuation parts according to the weak field, the color permittivity including the color field self- interaction is obtained. From this result, the nonlinear eigenfrequeney shift and the nonlinear Landau damping rate are obtained. Confronting the run of RHIC, the study about the signals of deconfinement and partial restoration phase transitions under extreme environment is the hot topic in high energy circles. In particular, because the FM signals: dileptons and photons can pene- trate the medium almost undisturbed and are considered to be the clearest ones, have drawn much attention. How to explain the strong enhancement of dileptons in the low ,~ k DOCTORAL DISSERTATION iii invariant mass region observed in the A ?A central collisions of CERES-NA45 is the hot topic in analyzing the EM signals. In exp~aining this kind of enhancements, because the lifetime of p is smaller than that of the fireball and the decay of p into dilepton can be completed in the fireball, the study about p meson decay in hadronic environ- ment is very crucial. Based on imaginarY finite temperature field theory. the effects of hot/dense hadronic environment on the spectral function of p meson is analyzed. It is found that hot/dense environment plays an important role to the spectral function: when the temperature or the density is not too high. the spectral curve vs invariant mass is becoming wider and the peak is shifted towards the high invariant mass region with the increase of temperature. However, in ultra high temperature or density envi- ronment, the peak is shifted towards lower region and the curve is changed narrower with the increase of temperature. In the invariant mass region M 憕.-?0.4 GeV?.6 Ge1~, the spectral function is enhanced very much. which contributes to the interpretation of dilepton enhancement results in relevant experi...