An application of second order approximations for the Green's function |
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Authors: | B Fuchssteiner |
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Institution: | 1. Institut für Theoretische Kernphysik der Technischen Hochschule Darmstadt, Deutschland
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Abstract: | In a previous paper there was developed an approximation theory for the Green's functions which gives approximations consistent with the conservation laws of the Hamiltonian. We have chosen a concept of reduction which is different and which leads to other approximations for the particle-hole Green's function than the usual concept of reduction. The particle-hole Green's function is the function $$\langle \Psi _0 |\tau \{ a_1^ + (0)a_2 (0)a_3^ + (t)a_4 (t)\} |\Psi _0 \rangle $$ where ¦Ψo〉 is the real ground state and τ stands for the time ordered products of the operators. Now, in this paper we want to give an example of an application of this theory. We present a second order approximation since the first order approximation is the well known Random Phase Approximation. |
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