标题： 热π介子气体中的π介子对形成和π介子色散关系 显示英文标题

标题： Pion-pair formation and the pion dispersion relation in a hot pion gas

摘要： 指出并详细讨论了基于玻色子间隙方程的热π介子气体中π介子对形成的可能性。 确定了π介子对凝聚（Evans-Rashid转变）的临界温度作为π介子密度的函数。 对于费米子，这种相变由两粒子传播子中极点的出现来标志。 在玻色系统中存在一个第二、更低的临界温度，与单粒子凝聚的出现有关。 在这两个临界温度之间，π介子色散关系从通常的准粒子色散变为低动量下的Bogoliubov型色散关系。 这推广了Evans等人对有吸引力的玻色子气体的非相对论性结果。 讨论了其对超相对论重离子碰撞中测量的包含π介子谱的可能影响。 显示英文摘要

摘要： The possibility of pion--pair formation in a hot pion gas, based on the bosonic gap equation, is pointed out and discussed in detail. The critical temperature for condensation of pion pairs (Evans--Rashid transition) is determined as a function of the pion density. As for fermions, this phase transition is signaled by the appearance of a pole in the two--particle propagator. In bose systems there exists a second, lower critical temperature, associated with the appearance of the single--particle condensate. Between the two critical temperatures the pion dispersion relation changes from the usual quasiparticle dispersion to a Bogoliubov--like dispersion relation at low momenta. This generalizes the non-relativistic result for an attractive bose gas by Evans et al. Possible consequences for the inclusive pion spectra measured in heavy--ion collisions at ultra--relativistic energies are discussed.