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4 questions
1vote
0answers
34views
Wick theorem for $N$-particle Matsubara green function: equal time contraction [duplicate]
I am wondering why, e.g., the book by Mahan, "Many-particle physics", mentions that contractions in Wick theorem for the $N$-particle Matsubara Green function between a pair of operators at ...
- 345
1vote
0answers
280views
Calculating a four-point Green function using Wick's theorem (problem 12.1 in Mandl & Shaw)
In problem 12.1 in Quantum Field Theory, Mandl & Shaw the aim is to calculate the four point green function $$ G^{\mu\nu}(x,y,z,w) = \frac{\langle 0 | T\big(A^{\mu}A^{\nu}\psi(z)\bar{\psi}(w)S\big)...
- 321
2votes
1answer
763views
Help with Wick's theorem in a $\phi^4$ QFT
QFT noob here. I am currently working out the momentum space two-point function for a $\phi^4$ qft in Euclidean space time, and considering the $\lambda^1$ order contribution, I am encountering a ...
2votes
3answers
539views
Correlation function of single annihilation/creation operator vanishes
I could not find anything on that on google, or here on physics stack exchange, which surprises me. My problem is, that I do not see, why exactly $$\left<a\right> = \left<a^\dagger\right> =...
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