Questions tagged [propagator]

propagator gives the probability amplitude for a particle to travel from one place to another in a given time, or to travel with a certain energy and momentum.

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How to understand long-range propagate without decay in time and space?

Assume there is a Green function: $$G=\frac{1}{(p^2+r)-\sum-\omega^2}$$ where $\sum$ is self-energy. We know that if the self-energy vanishes, the quasi-particle is well-define, and it can propagate ...
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Is the scalar propagator an even function?

The scalar propagator for the Klein-Gordon Lagrangian is given by: $$D(x-y)=\int \frac{d^{4} k}{(2 \pi)^{4}} \frac{e^{i k(x-y)}}{k^{2}-m^{2}+i \varepsilon}$$ I need to know if it is an even ...
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Formal identity involving fermion propagator in quantum field theory

I'm studying from here: Roberto Soldati - Field Theory 2. Intermediate Quantum Field Theory (A Next-to-Basic Course for Primary Education) I'm trying to understand and prove an equality at page 52, ...
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Self-energy series expression in terms of unperturbed Green function for exited states

I would like to understand how to arrive at the series in equation (36) in this paper https://arxiv.org/abs/cond-mat/0506438, specifically $$\Sigma(E) = V+VG'_0(E)V+VG'_0(E)VG'_0(E)V$$ where $G'_0(E)$ ...
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How is the quantum propagator related with Huygens principle?

Usually in quantum mechanics the wave function can be propagated via the so-called Kernel or Amplitude: $\Psi(x,t) = \int K(x,t;x',t')\Psi(x',t')dx'$. I have read in some paper that this comes from ...
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Simple Green's function question: Propagator for stationary particle?

Suppose the probability a particle transitions into a state of interest at time $t$ having position $x$ is $$\omega(x,t).$$ Once a particle enters this state it does not leave it, nor does its ...
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Feynman diagrams for gravity

Feynman rules is the basic tool to compute amplitudes in perturbation theory for a QFT. Here, I am trying to understand perturbation theory in GR around the flat space metric, in terms of Feynman ...
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Interpretation of the propagator

In quantum mechanics, it is clear that $\langle x|y\rangle = 0$ for $x\ne y$, where $|x\rangle$ is the state with the particle at position $x$. (Notice that this $|x\rangle$ is different from the ...
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1-loop correction to photon propagator

(May be it is a duplicate). I do not understand clearly how should I write down 1-loop correction to photon propagator. I know what is $i\Pi_{\mu\nu}(k^2)$ (I need only this specific correction) and ...
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No bound states if propagator is everywhere infinite?

Assuming the energy spectrum is discrete, the propagator for the time independent Schrodinger equation can be represented as $$G(x,y,E)=\sum_n\frac{\psi_n(x)\psi_n^*(y)}{E-E_n}.$$ The propagator's ...
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How does one calculate Fourier transform of Feynman propagator?

I am struggling with calculating the following integral on Sredinicki: How did he get the second line of (10.6)? That is, how did he calculate the Fourier transform of Feynman propagator?
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Confusion about functional derivative in path integral

If we act a functional derivative $$\frac{\delta}{\delta J(z)}$$On the expression$$\int\int d^4x d^4y \space J(x)\Delta(x-y)J(y)$$ where $\Delta(x-y)$ is Feynman propagator. What one should get is ...
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When can you simplify the $W$ boson propagator?

I have seen in several sources that the propagator of the $W$ boson is: $$\frac{- i \left( g^{\mu\nu} - \frac{P^\mu P^\nu}{m_W^2} \right)}{p^2 - m_W^2} .$$ But then in some calculations (usually ...
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How to grasp the limits of these two integrals? [duplicate]

I find some difficulty in understanding the limits of the two integral below (on Page 27 of Peskin & Schroeder's Quantum Field Theory): D(x-y)=\frac{1}{4\pi^2}\int_m^\infty d E \sqrt{E^2-m^2}e^{...
The optical theorem links the imaginary part of the forward scattering amplitude to the total decay width of a particle: $\mathrm{Im}\,M_{i\to i} = m\Gamma_{tot}$. Here \$\Gamma_{tot} = \frac{1}{2m} \...