Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [interactions]

Particle interactions are changes in the nature, number, or state of several particles, usually at a specific space-time point, underlying dynamics. They are represented by special "field interaction terms" in quantum field theory and normally entail interchanges of energy, momentum, and sundry quantum numbers. They include scattering, and particle creation and annihilation.

5
votes
0answers
90 views

Free Electron-Bond Electron Interactions

I am reading an introductory textbook on electronics: Practical Electronics for Inventors by Paul Scherz and Simon Monk. In a section discussing the motion of electrons in circuits, the textbook ...
4
votes
0answers
305 views

How can I see where this formula for a general vertex factor comes from?

I have been reading Srednicki from the beginning and doing all the exercises, and I hit a big roadblock at Q10.4, as I can't seem to figure out what Srednicki is doing in his solution. Luckily, I ...
4
votes
0answers
145 views

Is the phrase “coupling constant” interchangable with “ strength of interactions”?

Can I use the terms coupling constant and strength of interactions, interchangeably, or are there more subtleties to the term coupling constant that I am not aware of? Coupling Constants from ...
4
votes
0answers
113 views

How to prove that identical particles are attracted or repelled in a given spin-s interaction theory?

Let's assume that we have integer spin interaction theory (EM field, linearized gravity, arbitrary gauge spin s theory). How to prove the consequence that in interaction theory with spin $s = 2n$ two ...
3
votes
0answers
97 views

Renormalization group in time and space, finite size systems

I have few questions about RG. For completeness and clearness I'll start more or less from the beginning. Initially I have bare two-point propagator: \begin{equation} G_0(r)=\frac{1}{r} \end{...
3
votes
0answers
69 views

Interaction terms in the curved space Lagrangian

Apologies in advance if this has been posted before, I've browsed through the questions but couldn't find anything similar. I've been studying some QFT in curved space (mainly using the Birdell & ...
2
votes
0answers
57 views

How Forces are Represented from Quantum Computation or Entanglement Perspective?

In the fields of Quantum Computation and Entanglement there is content on the structure of quantum systems and artificial quantum systems like qubits and quantum cellular automata. I have even seen ...
2
votes
0answers
200 views

Electron - phonon interaction and perturbation theory

It might be not so clear what the question actually is, so I'll start with that: why do we often use perturbation theory for non-degenerate spectrum in solid state physics, while the spectrum of $H_0$ ...
2
votes
0answers
503 views

What is a soft photon?

I accidentally came across the words "soft photon" today after reading a few blogs. There was some discussion of special situations involving gauge redundancies and a theorem by Weinberg. What is a ...
2
votes
0answers
176 views

How do quantum fields really couple?

The term "coupling" between quantum fields refers to certain terms in the Lagrangian (density) $\mathcal{L}$ where the respective field operators appear together, e.g. $g\phi^\dagger\psi $ with ...
2
votes
0answers
123 views

Validity of the static limit of a dielectric function

In general, the dielectric function $\epsilon(q,\omega)$ reflects the spatial and temporal response of a condensed matter system to an applied potential. If we put an electron into an electron sea, ...
2
votes
0answers
91 views

In QFT, how can it be shown that the field out, ${\phi_{out}}$, is a free field if the field in, ${\phi_{in}}$, is a free field?

In the Dirac picture of QFT interacting fields, if the field in, ${\phi_{in}}$, is a free field, then I know that the field out, ${\phi_{out}}$ should also be a free field. How can this be shown? Let'...
2
votes
0answers
155 views

Adiabatic theorem in the regime of quantum optics

I am wondering whether there is a version of adiabatic theorem in the regime of quantum optics. My understanding of quantum optics involves with the interaction between photon and atom. This ...
2
votes
0answers
754 views

Question on the Gell-Mann Low equation

Question on the Gell-Mann Low Equation. In this paper, http://arxiv.org/abs/1205.3365, page 21, the author argues that if $t\to\infty(1-i\epsilon)$, all the terms in equation (193), $$ \mathrm e^{-iH(...
1
vote
0answers
36 views

Feynman rules for a general Lagrangian

How do I find the Feynman rules for a general Lagrangian density? For example the Lagrangian $$L = \partial_\mu \psi \partial^\mu \psi +a \psi\partial_\mu \psi \partial^\mu \psi+b \psi^2 \partial_\mu ...
1
vote
0answers
44 views

Non-minimal coupling between a neutral atom and the EM field

Let us say that I have neutral bosonic atoms interacting with an EM field. I can write down the Lagrangian as \begin{align} \mathcal{L}=\eta^{\mu\nu}\partial_{\mu}\phi\partial_{\nu}\phi^{\dagger}-m^2|...
1
vote
0answers
53 views

Feynman Rules from Lagrangian with charge conjugation matrix

I'm dealing with a doubly charged scalar singlet that interacts only with the right-handed muon as follows, $$\mathcal{L} = \lambda \psi_{R}C\psi_{R} \phi^{++},$$ where $\lambda$ is the coupling, $\...
1
vote
0answers
32 views

Why is the photoionization cross section smaller at higher photon energies?

I read that the photoionization of a ground state hydrogen atom for photon energies $h\nu > I_H$ (where $I_H$ is the ionization energy of $H$ at $13.6 \, \mathrm{eV}$ has a smaller cross section ...
1
vote
0answers
101 views

Why isn't energy conserved in time-ordered diagrams?

I'm new to particle physics, and I'm reading chapter 5 of Prof. Mark A. Thompson's "Modern Particle Physics", which talks about Time-ordered perturbation theory vs QED. However, in page 119 he wrote: ...
1
vote
0answers
182 views

Kallen-Lehmann representation derivation

I'm trying to understand the derivation of the Kallen-Lehmann representation given in Peskin & Schroeder (pages 211-214). I would really appreciate if anyone on here could answer a few questions I ...
1
vote
0answers
31 views

How fundamental electromagnetic interaction occurs in electrostatic case (say, between two resting electrons )?

Interaction between two resting charges (electrostatic case - in electrostatic field) is anyways electromagnetic (because we have only 4 fundamental interactions). Electromagnetic interaction means ...
1
vote
0answers
38 views

Eigenvalue equation for interacting Green's functions

Studying the articles "Topological Hamiltonian as an exact tool for topological invariants" (https://arxiv.org/abs/1207.7341) and "Simplified Topological Invariants for Interacting Insulators" (https:/...
1
vote
0answers
85 views

Visual simulation of elementary particles and interactions thererof?

Pardon me for a very stupid question, but knowing that SM predicts so much about sub-atomic particles, their interactions and whatnot, means that we have formalized these into some sorts of equations,...
1
vote
0answers
90 views

String interactions: intuitive vs worldsheet pictures

I am trying to understand precisely the interactions in open/closed string theories from several (interconnected) aspects: relation between the "intuitive" picture (by that I mean spatial sections of ...
1
vote
0answers
249 views

Matsubara Green's function

The RKKY coupling has the form of $\chi_{i,j}(r,r')= \frac{-2}{\pi} Im \int_{-\infty}^{\varepsilon_F} d\varepsilon \; Tr[\sigma_i G(r,r',\varepsilon) \sigma_j G(r',r,\varepsilon)]$. where i and j ...
1
vote
0answers
89 views

Finite-Temperature $\phi^{4}$ theory - Why is the massless $T\neq 0$ contribution diverging?

I'm following Chapter 3 of Kapusta and Gale's Finite-Temperature Field Theory here. I'm considering the following integral (the unrenormalized self-energy evaluated at zero-four momentum): $$ \...
1
vote
0answers
426 views

$\phi^{4}$ theory Feynman rules

One of the momentum space Feynman rules in $\phi^{4}$ theory (for correlation functions) is that for an external point with 4-momentum $p$ (with direction headed towards the external point), we need a ...
1
vote
0answers
306 views

Interaction Lagrangian with derivatives

I have a problem with derivatives in the interaction part of the Lagrangian. Considering the Lagrangian $${\cal L}=\frac{1}{2}\partial_{\mu}\phi\partial^{\mu}\phi+\frac{1}{2}\partial_{\mu}\psi\...
1
vote
0answers
46 views

Can the MSW effect be modified by non-standard neutrino-neutrino interactions?

The MSW effect describes how propagation of neutrinos through matter can resonantly enhance the neutrino mixing. The reason for this enhancement is that the presence of electrons in matter changes the ...
1
vote
0answers
535 views

What is a hard core in inter particle potential?

I am reading the book A Modern Course in Statistical Physics by Reichl. In it, there is the following statement The theory of interacting semi-classical fluids is also easily described by the Grand ...
1
vote
0answers
62 views

Comparison of vacua and annihilation operators of Klein-Gordon theory and phi-fourth theory

The ground state or vacuum of an interacting theory is, in general, different from the ground state or vacuum of a free theory. In what cases are the two vacuums the same as each other? Can an ...
1
vote
0answers
36 views

Trinification lepton Yukawa interactions

We have a trinification model of $SU(3)_c\otimes SU(3)_L\otimes SU(3)_R$, where the first is the usual colour group, the second a left $SU(3)$ and the third a right $SU(3)$. As usual, leptons and ...
1
vote
0answers
89 views

Creation of momentum on vertex (quantum field theory)

For a an interaction term like $g(\overline{\psi} \gamma^\mu \psi) \partial_\mu \phi$ in which $\psi$ is a Dirac spinor and $\phi$ a scalar field (d=4), should we expect this vertex to have a momentum ...
1
vote
0answers
85 views

Does the force of releasing the latch of a spring-latch contraption affects the force generated by the spring?

There is this contraption in my class, where a rod is attached to a latch and a spring. By pulling the latch back behind a piece of metal, the latch is secured, the rod if pulled back and the spring ...
1
vote
0answers
72 views

Do interaction free experiments violate Quantum Physics?

Although I know that interaction free experiments come under Quantum Physics, Don't the kind of violate the Heisenberg uncertainty principle? Because you get a value without interacting with the ...
1
vote
0answers
53 views

Is it possible for quasiparticles to form charge density wave of quasiparticles?

What if the quasiparticle has fractional charge? -----UPDATE------ For example, 1d kink has e/2 charge, if view kink like electrons in 1d (we know there is 1d charge density wave of electrons), is ...
1
vote
0answers
75 views

Interactions with high helicities particles

As it can be shown, there are no interacting helicity-3 (and higher) particles (i.e., massless spin-3 or higher particles) in soft limit (small momentums of emitting particles of given helicity). Сan ...
1
vote
0answers
101 views

Exotic coupling

I have encountered the minimal coupling between a field and charges before $$H = \frac{1}{2m}(p-qA)^2,$$ whereby I am considering the classical case. The description minimal leads me to ask if ...
1
vote
0answers
518 views

Range of forces from mass of force carrier?

Why is $\frac{\hbar}{mc}$ a good estimate of the range of the four forces, where $m$ is the mass of the carrier particle of the force? Inputting the pion mass gives $1.4\ \mathrm{fm}$ for the hadronic ...
0
votes
0answers
26 views

How do interaction terms appear in the Lagrangian?

How does forcing the Lagrangian to be invariant under $U(1)$ group give rise to the electromagnetic interaction term?
0
votes
0answers
48 views

How to determine which force mediates an interaction?

I have been given an assignement gives me a number of interactions, asks me to determine which, among these interactions are permitted under conservation laws (Charge, Baryon number, Leptonic numbers, ...
0
votes
0answers
7 views

Why in the iron based superconductor interband interaction is dominating?

What is the mechanism of intraband and interband interaction in the iron based superconductor? and Why interband interaction is dominating?
0
votes
0answers
46 views

Can all fields contribute to the potential energy that appears in QM Hamiltonian?

Most importantly: can that potential energy in the QM Hamiltonian able to describe the motion of a single particle in an external electromagnetic field? Background: In non-relativistic QM using the ...
0
votes
0answers
23 views

Deriving effective interactions, e.g. phonon-mediated electron-electron interaction

Upshot of the question: how can I derive the effective electron-electron interaction brought about by the electron-phonon interaction? I've read derivations of the electron-phonon interaction and ...
0
votes
0answers
48 views

Propagators in interaction with derivatives

Given a Lagrangian density containing an interaction with derivates, it's easy how to guess the Feynman rules for vertexes. However i was wondering about propagators: in S-matrix expansion it's ...
0
votes
0answers
220 views

Derivation of the complete Bethe Bloch formula

I can not find anywhere the explicit calculation for the complete Bethe Bloch formula including all the correction factors. I would like to have at least one idea of ​​the calculation that is actually ...
0
votes
0answers
61 views

Calculation of a 4-point function by path integrals

In Srednicki's book in chapter 8 a four-point function is computed as a sum of products of propagators: $$<0|T\phi(x_1)\phi(x_2) \phi(x_3)\phi(x_4)|0> = \frac{1}{i^2}[\Delta(x_1 -x_2)\Delta(...
0
votes
0answers
53 views

Properties of Feynman diagrams in Fermi's effective interaction theory

What are the properties of the Feynman diagrams in Fermi's effective interaction theory and how can one draw a Feynman diagram in this theory in relation to the Feynman diagram in the standard model ...
0
votes
0answers
66 views

Lagrangian term for multiple particle interactions in curved spacetime

I have the following question. Suppose one wants to describe the dynamics of $N$ interacting classical particles in a metric background given by the line element: $$ds^{2}=g_{\mu\nu}dx^{\mu}dx^{\nu}.$$...
0
votes
0answers
25 views

How would an interaction with a single charge, and a charged weightless carrying particle behave?

We learnt about, among the other three fundamental interactions, the strong interaction. The particles that are affected by it are those with color-charge. It's carrying particles, gluons, have a ...