So we should use RPA to sum all the rings to infinite order.The unphysical pole may appear during solving the Dyson equation, known as the Landau ghost in QED.

• 本文按照Tanaka的思路，给出了有限密度的情况下传播子的谱表示，证明了这样做的结果是不含有鬼点的，在不做任何近似的情况下将其应用到响应函数中；