【摘要】 在N_σ~3×N_τ(N_τ=1)的高温格点U(1)模型中,对序参数Polyakov线<L>作累积展开计算到五级近似。重点在于讨论累积展开在中间耦合区的行为,从累积展开与关联长度的联系阐明在中间耦合区高阶展开的必要性。采用n级展开对零级展开的修正为零的条件定n级计算中的变分参数,结果显示,不仅在强、弱耦合区,而且在中间耦合区(除了相变点附近)都与蒙特卡罗模拟有较好的符合,随着近似级别的增高,可信的计算可以越来越逼近相变点。这可能是变分累积展开方法作为近似解析方法的一大优点。更多还原

【Abstract】 The order parameter, Polyakov line <L>, of the U(1) gauge model on N_σ~3×N_τ(N_τ=1) lattice by using the cumulant expansion is calculated to the 5-th order. The emphasis is put on the behaviour of the cumulant expansion in the intermediate coupling region. The necessity of higher order expansion is clarified from the connection between the eumulant expansion and the correlation length. The variational parameter in the n-th order calculation is determined by the requirement that corrections of the n-th order expansion to the zeroth order expansion finish. The agreement with the Monte Carlo simulation is obtained not only in the weak and strong coupling regions, but also in the intermediate coupling region except in the very vicinity of the phase transition point.更多还原