Theoretical study of beauy-ins collisions at exirame high enngiro

我们对超相对论重离子碰撞产生的致密物质的预期性质及其实验探测进行了理论研究。1）π介子干涉测量中的阴影效应：众所周知，高能碰撞中产生的一对全同粒子之间的动量关联可以用来提取粒子源的时空几何信息。我们研究了π介子和π介子源之间的末态相互作用对这种关联的影响。我们发现，如果π介子是从一个强源（如夸克胶子等离子体）中发射出来的，那么这个强源就像一个π介子的强吸收体，这可能导致π介子的动量关联在π介子的相对动量很小时被抑制。2）有限温度下的手征相变：本文采用自洽Hartree近似下的线性σ模型研究了平衡态下的手征相变。以前的工作遇到的困难违反Goldstone定理的手征极限。我们制定了一个新的自洽的近似方案，尊重戈德斯通定理明确。结果表明，在这种近似下，由于介子场的长程涨落，在相变区介子场的有效质量变小，在手征极限下，理论预言了一个（弱的）一级相变。3）膨胀量子场动力学的变分方法：我们用泛函薛定谔图中的变分波泛函描述了膨胀量子场的动力学。对于自由场，变分波函数选择为广义高斯形式。本文对由变分原理导出的运动方程构造了一族boost变分解。

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.