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Self energy, 1PI, and tadpoles
I'm having a hard time reconciling the following discrepancy:
Recall that in passing to the effective action via a Legendre transformation, we interpret the effective action $\Gamma[\phi_c]$ to be ...
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No mixing in light cone perturbation theory
In hep-ph/0609090, Triumvirate of Running Couplings in Small-x Evolution, Kovchegov et. al. calculated the running coupling correction to the Jalilian-Marian, Iancu, McLerran, Weigert, Leonidov and ...
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Question about the perturbative renormalization group
I'm currently learning about the renormalization group (RG) in condensed matter physics and just want to clarify a couple of things:
When doing the RG transformation, there's a flow to a fixed point. ...
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Do perturbative renormalization groups help one understand when perturbation theory can be used in general?
If, as I asked in this question, a relevant operator in a renormalization group transformation can't be used in a perturbative expansion since it becomes large as the transformations are applied, does ...
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Derivation of Brillouin-Wigner theory for coupled subpaces
I recall faintly from my quantum theory lecture that there was a really neat way to derive Brillouin-Wigner perturbation theory for the special case of two coupled subspaces that involved a geometric ...
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What is better than time-dependent perturbation theory if the pointer states aren't energy eigenstates?
Time-dependent perturbation theory works excellently if the interaction is weak and the pointer states are approximately energy eigenstates. However, what if the pointer states are not remotely energy ...
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Perturbed stress-energy tensor in a cosmological context?
In the theory of cosmological pertubations, we can write the metric of a null-curvature expanding Universe as :
$ds^2 = -c^2\left(1+2\frac{\psi}{c^2}\right)dt^2 + a^2 ...
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Brillouin-Wigner perturbation theory and the useful perturbed energy
Well, when you are working with the Brillouin-Wigner perturbation theory, the corrected energy for the perturbed system, after the first order of correction, is given in terms of the unknown variable, ...
