Questions tagged [self-energy]
Quantum-mechanical object that captures some of the characteristics of particles associated to interactions with themselves and with other particles, such as the change in its mass as a function of its energy. Particularly useful in quantum field theory, either for relativistic particle physics or condensed matter physics. Although it also makes sense as a classical concept, it mostly has fallen into disuse nowadays.
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Tadpoles and photon self-energy in QED
Tadpoles diagrams are zero in QED for many reasons, one of them is the Lorentz invariance of the vacuum expectation value of the current.
Without considering the external photon line (as Peskin &...
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Scalar self-energy in $\mathcal{N}=4$ SYM in position space
In this paper (BMN Correlators and Operator Mixing in $\mathcal{N}=4$ Super Yang-Mills Theory, 2002), the authors give the following expression for the self-energy of the scalar propagator in $\...
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In electron transport calculations, should lead self-energies always be diagonal in a mode energy eigenbasis?
In electron transport calculations for semiconductor devices, the non-equilibrium Green's function method is often used. The Green's function takes the form
$$G = \left[EI-H-\Sigma_L-\Sigma_R\right]^{-...
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1answer
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One-loop diagram self-energy
I need to find the diagram contributing to the self energy of $\varphi$. Say I had an interaction term in the Lagrangian 2 $\varphi$ real scalar fields, and one $\psi$ real scalar field, $\varphi^2\...
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How to calculate the Fock exchange interaction self-energy of a system in momenttum space
I have a Hamiltonian in the momentum space which has a strong non-local electron-electron interaction.
I know that I have to find its corresponding exchange self-energy and solve the Dyson equation ...
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How to find the functional self-energy?
I have a system with $e$-$e$ interaction. After using the mean field approximation, my Hamiltonian has the following form:
$H = H_0 + H_I$, which $H_0$ is the non-interacting and $H_I$ is the ...
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1answer
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Iterative Greens function calculation
I have a Hamiltonian which has an interactive and non-interactive parts.
$H = H_0 + H_I$
$H_I$ comes from the non-local electron-electron interaction and must be calculated self-consistently.
I ...
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Why is the self-energy for quarks in $d=2$ Large $N$ QCD only order $g^2$?
In an interesting article by 't Hooft , he is able to find the exact quark propagator, in the large $N$ limit of QCD. He finds that the full 1PI self-energy is given by:
$$\Gamma(p)=-\frac{g^2}{2\pi} \...
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Is the issue of self force on point charges solved by QED?
I know that classically self force is not a very tractable problem for point particles, although some attempts have been made in various ways over the years.
I also know that even in QED ...
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How to calculate thermal corrected masses of Higgs and Gauge bosons?
How are the self energies of scalars and gauge bosons at finite temperature calculated in the process of determining the 1-loop resummation of Debye masses? I have seen some papers where the explicit ...
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Using second order perturbation to calculate electron self-energy caused by electron-phonon interaction
Assume the electron-phonon interaction is given by
$$
H_{ep} = \sum_{k q} D(q) c_{k+q}^\dagger c_k (a_q + a_{-q}^\dagger).
$$
In the theory of superconductivity, the electron-electron effective ...
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1answer
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Why do the Euler-Mascheroni constant $\gamma$ and $\ln 4\pi$ not show up in observables (renormalisation of electric charge)?
The one-loop contribution of the vacuum polarisation of the photon after using dimreg is given by
$$\Pi_2^{\mu\nu}= e^2 J(q) \left(\eta^{\mu\nu} - \frac{q^\mu q^\nu}{q^2}\right),$$
with the metric ...
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Feynman self-energy diagrams
In the Feynman picture, I don't understand how virtual photons in the self-energy diagram for a rest-frame electron can have energies that exceed $2m_e$. Aren't negative energy states of the electron ...
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Why isn't a quark-antiquark loop included in the photon self-energy corrections?
In QED, the Lagrangian has a term $\bar{\psi}A^\mu\psi$, which gives a correction to the photon propagator, where the loop is made of a pair electron-positron, with the 1st order diagram:
In the ...
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Deriving relation between pole and running quark masses
How do I compute quark self energy and use it in order to derive detailed relation between pole and running quark mass?
If I do it for one loop, I should use this for running mass:
$\mu^2\times\...
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1answer
135 views
First-order Contribution to the Self-energy Operator
In Altand and Simons' book 'Condensed Matter Field Theory,' on page 225 they claim that the first-order contribution to the self-energy (effective mass) operator reads
$$\big[\Sigma_p^{(1)}\big]^{ab} =...
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Self-energy series expression in terms of unperturbed Green function for exited states
I would like to understand how to arrive at the series in equation (36) in this paper https://arxiv.org/abs/cond-mat/0506438, specifically
$$\Sigma(E) = V+VG'_0(E)V+VG'_0(E)VG'_0(E)V$$
where $G'_0(E)$ ...
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2answers
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Symmetry factor of gluon self-energy
In Peskin & Schroeder, p.523, they give the diagram contributing to the gluon self-energy that arises from the 3-gluon vertex, and they claim that the $1/2$ factor is a symmetry factor:
How can ...
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1answer
111 views
Self-energy in two scalar Yukawa interaction
Considering the Lagrangian of two scalar fields in $d=4$:
$$\mathcal{L}=\frac{1}{2}(\partial\phi)^2-\frac{1}{2}m^2\phi^2+\frac{1}{2}(\partial\chi)^2-\frac{1}{2}M^2\chi^2-g\phi^2\chi$$
What would be ...
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Computation of the self-energy term of the exact propagator for $\varphi^3$ theory in Srednicki
In M. Srednicki "Quantum field theory", Section 14 -Loop corrections to the propagator-, the exact propagator $\mathbf {\tilde \Delta} (k^2)$ is stated as
$$\frac{1}{i} \mathbf {\tilde \Delta} (k^2)...
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1answer
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How to know how the self-energy changes the mass?
Suppose we have a Green's function of the typical form
\begin{equation}
G(k)=\frac{1}{k^2-m^2-\Sigma(k)}
\end{equation}
where $\Sigma(k)$ is the self energy of that particle. How exactly can we ...
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1answer
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How to obtain the quasiparticle equation from Dyson equation?
The problem is formulated as follows:
Dyson equation for zero temperature Green's function:
\begin{equation}
\left[
i\dfrac{\partial}{\partial t_1} - h(\vec{r}_1)
\right]
G(1,2)-\int d3 \Sigma(1,3)G(...
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1answer
431 views
Self-energy of conducting shell
While calculating self energy of a conducting shell we integrate $Vdq$,where $V=\frac{q}{4π\epsilon r}$, but when the $dq$ charge is bought close to the shell it changes the charge distribution on the ...
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1answer
284 views
Combinatorics geometric series two-point function
In this answer Proof of geometric series two-point function it is said:
Now what about the coefficients in front of each Feynman diagram? Due to the combinatorics/factorization involved it ...
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1answer
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Are problems with self-energy of point charge in classical electrodynamics solved by field quantization?
Classical electrodynamics gives strange results when considering a moving charge in its self generated field (Abraham-Lorentz equation).
Some 50 years ago there were many efforts and publications ...
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1answer
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2PI-effective action and functional derivatives
I'm trying to work out the 2PI-effective action for complex scalar fields.
Introducing a multi field index $(a,b,c...)$ the complex conjugation and all other degrees of freedoms are suppressed, and ...
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0answers
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Self-energy that does not obey sum rule
Analytically, I calculated a self-energy $\Sigma(\omega)$, for which I verified that
1) $\text{Im}\big[\Sigma(\omega)\big] \leq 0$ for all $\omega$ and specifically $\text{Im}\big[\Sigma(0)\big] = 0$,...
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1answer
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Problem with converting Integral to Gamma functions (from HQET heavy quark self-energy diagram)
In the calculation of HQET radiative correction, I came across the Equation:
$$\int_0^{\infty}d\lambda ~ \lambda^{-\epsilon}(\lambda+\omega)^{-\epsilon} = \frac{1}{2\sqrt{\pi}}\Gamma(\epsilon-\frac{1}{...
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Geometric series of two point function and self energy
This question is related to this question Proof of geometric series two-point function.
Suppose we have a graph $A$ with a symmetry factor $s_1$. According to Srednicki (chapter 9, eq. (9.13)) for a ...
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1answer
232 views
Proof of geometric series two-point function
In deriving the expression for the exact propagator
$$G_c^{(2)}(x_1,x_2)=[p^2-m^2+\Pi(p)]^{-1}$$
for $\phi^4$ theory all books that i know use the following argument:
$$G_c^{(2)}(x_1,x_2)=G_0^{(2)}...
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1answer
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Proof of 1-particle irreducible (1PI) diagrams
If we split the effective action into
$$Γ[Φ] =\frac{1}2ΦiG_0^{-1}Φ + Γ^{int} [Φ]$$
we can show that the full propagator is given by
$$G= i[iG − Σ]^{-1}$$
With
$$Σ=-Γ_{ΦΦ}^{int} [Φ]$$
Here $Γ_{...
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Question about Gluon self-energy diagram/symmetry factor
I am a qft beginner and have a question:
In Peskin & Schroeder chapter 16.5 there is given an expression for a gluon self energy diagram:
According to the feynman rules we get
$$\frac{1}{2} \int ...
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1answer
558 views
Diagrams involved in 1-loop electron self-energy in QED
I'm following the derivation of electron self-energy at 1-loop in QED on Peskin-Schroeder, page 216. To second order in the coupling the considered diagram (7.15) is
The 2-point correlator at second ...
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1answer
277 views
Where are the poles of the one-particle Green's function located in the complex plane?
This post is a followup question to: How to get an imaginary self energy?
In the cited post, the two following representations for the one-particle Green's function are shown:
$$G(k,\omega) = \...
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0answers
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Infrared cutoff in the Kramers-Kronig relation for the marginal Fermi liquid
I am going through Andre-Marie Tremblay's derivation of the real part of the self energy in his lecture notes on the many-body problem. On page
254, if we take the imaginary $\Sigma''(k,\,\omega)\sim \...
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1answer
151 views
Asymptotic relation of Green's function for diverging self energy
I am considering the derivation on pages 64 to 66 of Zagoskin's Quantum Theory of Many-Body Systems. They consider a Green's function in the Lehmann representation:
$$ G(p,\,\omega)=(2\pi)^3 \sum_s \...
2
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1answer
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Integrals involving Bose-functions (Computational)
In short, I'm looking for some advice/literature how to deal numerically with Bose function.
My physical problem is to calculate a coupled set of Self-energies, thermal loop integrals, self ...
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1answer
137 views
Why electron self-energy and other processes like vacuum polarization is not possible classically? [closed]
Why electron self-energy and other processes like vacuum polarization is not possible classically?
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One-Particle Self-Energy (Yang-Mills)
I've been asking about an interesting question when i was calculating the self energy of a Gauge boson in Yang-Mills theory.
I think that the correct way to think this problem is: the incident ...
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1answer
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If 2 particles produce a potential equal to $\frac{k}{r}$ for each position $r$, how can I deal with the infinities from self-energies?
Sorry if the title is a bit floppy. I am studying two particle systems and their energy. I was given that (equation 1):
$$\mathbf F=-\mathbf \nabla U.$$
For a potential $U$, which is the same for ...
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1answer
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Is Ward identity really satisfied by the photon's self energy?
The one-loop self-energy of the photon,
,
when contracted with the external momentum $k^\mu$ gives the following difference of integrals where the integration variable in the first term is shifted ...
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2answers
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How do we decide the perturbation term in the Hamiltonian and what's the difference for the self-energy due to different perturbation terms?
The final result of many-body perturbation theory based on Green's function method can be organized into the famous Dyson equation:
$$G = G_0 + G_0 \Sigma G=G_0 + G \Sigma G_0 \tag{1}$$
where $G/G_0$ ...
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1answer
198 views
Deriving relation for gravitational self energy
My book says $U_{self}=\dfrac{-GM^2}{2R}$ for the hollow sphere, I tried deriving it as:
Suppose mass constructed is $m$, Work done on bringing mass $dm$ from $\infty$ to $R$ is $$dW=dm(V_{R}-V_{\...
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1answer
79 views
The electric field generated by a point charge becomes infinite when distance tends to zero. What physical meaning does this have? [duplicate]
What follows is from Professor Barton Zwiebach of MIT:
The only problem with such a large field is an infinite self-energy
of the point particle limit. This problem is not really there in QED, as
...
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1answer
597 views
Difference Between Vertex Function and Self Energy
I am trying to understand the difference between the 2-point vertex function and the self energy. In many presentations, they are described in ways that seem nearly equivalent, yet as I work through ...
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1answer
689 views
Analytical expression for Hartree-Fock diagram
The picture above is taken from "introduction to many-body physics" by Coleman. When I try to write down the momentum space expression for the two diagrams, I got the same expression for the first one,...
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2answers
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How to correctly understand these “1-particle-irreducible insertions”?
In QED, when dealing with the vacuum polarization and the photon propagator, some authors like Peskin & Schroeder introduce the so-called "1-particle irreducible" diagrams. These are defined as:
...
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1answer
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Self-energy of an electron
In his 1947 paper, Bethe states that the self-energy of an electron in a quantum state $m$, due to its interaction with transverse electromagnetic waves is
$$W = -\frac{2e^2}{3\pi\hbar c^3}\sum_{n}\...
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2answers
229 views
Why is it the finite piece of the self-energy often neglected to define the physical mass?
Using the bare perturbation theory, for a $\lambda\phi^4-$theory in $d$-dimensions, the regularized self-energy turns out to be $$\Sigma=-\frac{\lambda_0 m_0^2}{16\pi^2\epsilon}+\text{finite}\tag{1}$$ ...
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1answer
186 views
Did Feynman ever solve the problem of the difference between bare mass and self-energy of the electron?
The question had to do with the idea that space was filled with particles and that electrons could only exist in specific locations, and same with positrons in the "holes."
But if the electron has ...
