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5 questions
2votes
3answers
539views
Correlation function of single annihilation/creation operator vanishes
I could not find anything on that on google, or here on physics stack exchange, which surprises me. My problem is, that I do not see, why exactly $$\left<a\right> = \left<a^\dagger\right> =...
- 51
2votes
1answer
297views
Time ordering and Fourier transform
I was trying to find some insight into the Fourier transformed Green's function and I ran into something that I don't quite understand. When I try to Fourier transform the creation and annihilator ...
5votes
3answers
893views
Proof for a time-ordering equation in Negele & Orland (1998)
Let $T$ be the time-ordering operator which orders operators $A_1(t_1), A_2(t_2), \ldots$ such that the time parameter decreases from left to right: $$T[A_1(t_1) A_2(t_2)] = A_2(t_2) A_1(t_1) \text{ ...
18votes
3answers
3kviews
A curious issue about Dyson-Schwinger equation (DSE): why does it work so well?
This question comes out of my other question Time ordering and time derivative in path integral formalism and operator formalism, especially from the discussion with drake. The original post is ...
- 4,095
24votes
2answers
10kviews
Time ordering and time derivative in path integral formalism and operator formalism
In operator formalism, for example a 2-point time-ordered Green's function is defined as $$\langle\mathcal{T}\phi(x_1)\phi(x_2)\rangle_{op}=\theta(x_1-x_2)\phi(x_1)\phi(x_2)+\theta(x_2-x_1)\phi(x_2)\...
- 4,095
