Theoretical study of beauy-ins collisions at exirame high enngiro

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We conducted a theoretical research on the expected properties of dense matter produced in ultra-relativistic heavy ion collisions and their experimental probes. Progress has been made in the following problems :1) Shadowing effects in pion interferometry : It is well known that the momentum correlation between a pair of identical particles produced in high energy collisions can be used to extract information on trhe space-time geometry of the particle source. We studied how such correlation is affected by the final state interaction between the pions and the pions source itself. It was found that if the pions are emitted from a strong souce, such as a quark-gluon-plasma, the source acts as a strong absorber of pions and this may result in suppression of the momentum correlations at small relative momenta of pions.2) Chiral phase transition at finite temperature in the linerar sigma model : We studied the chiral phase transition in equilibrium using the linear sigma model in a self-consistent Hartree approximation. Previous works had encountered difficulties of violating Goldstone's theorem in the chiral limit. We formulated a new self-consistent approximation scheme which respects the Goldstone theorem explicitly. It was shown that in this approximation the theory predicts a (weak) first order phase transition in the chiral limit due to the long range fluctuations of meson field whose effective masses become small in the transition region.3) Variational approach for dynamics of expanding quantum fields : We descibed the dynamics of expanding quantum fields in terms of variational wave functional in the functional Schrodinger picture. The variational wavefunctional is chosen in a generalized gaussian form, as for the free field. We constructed a family of boost in variant solutions to the equations of motion derived by the variational principle.