Interaction Definition and 653 Threads

When we start by postulating local SU(2) gauge invariance for our weak isospin doublets \begin{align} \psi &= \begin{pmatrix} \nu_{e} \\ e^{-} \end{pmatrix}_{L} \end{align} etc., we have to introduce massless gauge fields to preserve the Lagrangian's invariance. For SU(2) this demands 3...

When current flows through the armature winding of a dc motor, what exactly happens in there that produces the torque? Is there a force due to the interaction between two magnetic fields or Lorentz force acts on the conductor electrons? Basically, why does motoring effect take place? Is it due...

The problem statement. When an exercises say " the interaction in a QFT has dimensions Δ" , what does it mean?, it means the field or the Lagrangian has this mass dimension? In this exercise I'm trying to find the classical beta function (β-function) for the assciated couling.

In QFT, we can expand the propagator and obtain the diagrammatic expansion to build up the Green's function. If we have a hamiltonian of the type H = H_{0}+V, where V is the perturbation, we can build up the Feynman diagrams,and if we could build up all of them to infinite order, we would...

Hi there, so my question is as follows. I understand that only the weak interaction can change the flavour of a quark, but why? Idea 1: It's due to the change in flavour also meaning a change in mass, thus a massive exchange particle is needed (gravity is negligible so forget the massive...

Hello everyone, I would like to ask a couple of questions related with the interaction mechanisms of photons and electrons with matter. Through searching about this subject, I have concluded that they both have different penetration depth and different interaction mechanisms. But apart from...

What are the conditions necesairy to collapse a wave function of a electron, photon or an atom (alpha particle mostly?). Wavelength? Asking because I cannot understand why in this video the wave function does not collapse in this box. Seems like in the outside there should be massive...

Hi, What is the basic idea about particle interaction in QM? Say you have first one single charged particle in an "empty universe". Here I think the first issue is given: That's impossible, you'll need masses (or better: energy) from a GRT view. Okay, say we watch this single charged...

Hi there, I've been reading a textbook on Physics as applied to nuclear medicine, in particular focusing on how photons interact with matter. The textbook states (without reference) that "there are nine possible interactions between photons and matter, of which only four are of significance to...

Regarding interacting green's function, I found two different description: 1. usually in QFT: <\Omega|T\{ABC\}|\Omega>=\lim\limits_{T \to \infty(1-i\epsilon)}\frac{<0|T\{A_IB_I U(-T,T)\}|0>}{<0|T\{U(-T,T)\}|0>} 2. usually in quantum many body systems...

Homework Statement A metal sphere, with charge q1=-2.80μC is held still and off the ground on an insulating rod. Another smaller metal sphere with charge q2=-7.80μC is projected towards q1. When the two spheres are 0.80m apart, q2 moves at 22ms-1. Assume the spheres are point charges, neglect...

I was studying my notes and specifically for the ##e^+e^- \rightarrow \mu^+ \mu^-## process, cross section is given by \sigma = \frac{4\pi}{3} \left( \frac{\alpha \hbar c}{W} \right)^2 where ##\alpha = \frac{g_{EM}^2}{4\pi}## and ##W## is the centre of mass energy. Is this the same for...

Does anyone know any good introduction to V-A weak interaction theory?

I just want to know what is the effect of proton spin & coloumbs repulsive force & nuclear interaction on binding energy. Plzz explain with derivation.

I just want to know what is the effect of proton spin & coloumbs repulsive force & nuclear interaction on binding energy. Please explain with derivation.

I have just started reading about a classical electromagnetic treatment of light-matter interaction (beginning with dispersion relations, and then moving on to the standard phenomena - reflection, refraction, etc.). The discussion begins with a forewarning that light is not 'continuous' as the...

I learned that photons can exite and ionize electrons in an atom, bring them to higher energy level etc. However I've seen a few questions on electrons bombarding electrons in an atom and exiting the orbital electrons to higher energy level. Is this the same as the photoelectric effect when...

"An interaction is required to manifest physical reality because it creates distinctions." my friend referring to the double-slit experiment, is it true? He said that the physical world, in order to exist, we need to interact (with our senses) lol

Hello. I'm looking for a good book that explains light matter interaction comprehensively and specifically addresses photoluminescent materials (such as phosphor powders). I wanted this reference to get detailed answers to, e.g.: what is the mechanism of scattering, absorption and emission...

Homework Statement Two horizontal parallel conducting rods are connected such that a conducting crossbar free to slide along them has a constant current I running through it (Figure 1) . The rods are separated by a distance ℓ and are in an external uniform magnetic field of magnitude B directed...

The question is for which of the ##1P## meson states - ##1^{1}P_{1}, 1^{3}P_{0},1^{3}P_{1}, 1^{3}P_{2} ## ##D_{s}## states decaying to a ##1S## state is the decay: ##D_{s}**^{+} -> D_{s}^{+}\pi^{0} ## possible? Solution So the strong interaction conserves parity. Parity of meson is given by...

I won't go into any details because it is really not important. In class we handled a problem dealing with an incoming photon that crashes into an electron, the electron gains momentum and a new photon is emitted too. My first question is about Maxwellian E&M. I understand that according to...

Homework Statement [/B] 1.) A muon is created by a cosmic ray interaction at an altitude of 60km. Imagine that after its creation, the muon hurtles downward at a speed of 0.998, as measure by a ground-based observer. After the muon’s “internal clock” registers 2.0μs , the muon decays? a.) If...

I did the math and figured that Fel between two protons at 1 mm is 2.307E-22 N, and the Fg at the same distance is 1.867E-36 obviously these values change with the number of protons, and distance. this is an issue because I'm trying to imagine a hypothetical object as charged as possible while...

Homework Statement Neglecting hydrogen-bonding, calculate the interaction energy between (i) H3O+ and H2O and (ii) H3O+ and H3O+, if each pair is separated by 0.3 nm and assuming that the aqueous solvent can be treated as a medium with constant relative permittivity. Using your result...

Homework Statement Estimate the energies of interaction at 25 °C between (i) two hydrogen molecules and (ii) two nitrogen molecules, if each pair is separated by 0.3 nm. Explain fully and clearly your reasoning and any assumptions you make in your answer. State the source of the values of any...

Hello! In Van der Waals interaction, how to prove that : H= - (2*e^2*x1*x2) / R^3 ?

Can anyone help with an ongoing argument we are having. When a particle interacts with a vector field e.g. the electric field, it experiences a force trying to move it which depends on the particle charge and the local field condition, - but when it interacts with a scalar field e.g. the Higs...

I´m looking for a software that would allow me to test atom interaction acurretly in 3D, with public variables (i.e. customizable parameters) like the pressure and the temperature. I´m looking for something that takes into account S, P, D orbits with their real shape and the real numbers of...

I found this in a Phd thesis consider a two level atom interacting with the electromagnetic field. The atom is described by ##H_{at} = \hbar ω_0 J_z## a monomode electric field is described by ##H_{em} = \hbar \omega (a^\dagger a + 1/2)## We have ##E = E_0(a^\dagger + a)## and the dipolar...

The standard Heisenberg picture equation of motion is $$i\hbar\frac d{dt}A_H=[A_H,H],$$ assuming no explicit ##t##-dependence on the Heisenberg-picture operator ##A_H##. I've been trying to go directly from this equation to the corresponding interaction-picture equation, $$i\hbar\frac...

Hi everyone, I have a simple and foolish question. I want to compare the energy of a given mass (obviously e=mc2); let's say the energy of a hydrogen atom, with the energy that binds together the fundamental particles of that atom (strong interaction). I know that e=mc2 holds always true, and...

Homework Statement (a)Find splitting between F=0 and F=1 in hydrogen (b) Find the constant ##A## and nuclear magnetic moment Homework EquationsThe Attempt at a Solution Hyperfine splitting is given by: H_{hf} = \frac{A}{2} \left[ F(F+1) - I(I+1) - J(J+1) \right] The intervals are given by...

Homework Statement I am trying to calculate the following quantity: $$<0|T\{\phi^\dagger(x_1) \phi(x_2) exp[i\int{L_1(x)dx}]\}|0>$$ where: $$ L_1(x) = -ieA_{\mu}[\phi^* (\partial_\mu \phi ) - (\partial_\mu \phi^*)\phi] $$[/B] I am trying to find an expression including the propagators...

In all the places where Spin-Orbit interaction is discussed, the equations are derived by going to electron's rest frame and considering the interaction of nucleus' magnetic field with electrons spin magnetic moment. But from SR, we know that there as to be an explantion from the nucleus's rest...

The corrections to the energy per electron in a jellium model (uniform distribution of positive ion charge approximation to the regulated long range order ionic array) is given by (in units of Ry) $$E/N = \frac{2.21}{(r_s/a_o)^2} - \frac{0.916}{(r_s/a_o)} + 0.0622 \ln (r_s/a_o) - 0.096 +...

Hello! This is my first time posting, so please correct me if I have done anything incorrectly. There's something that I don't understand about the spin-orbit interaction. First of all I know that [\hat{S} \cdot \hat{L}, \hat{L_z}] \ne 0 [\hat{S} \cdot \hat{L}, \hat{S_z}] \ne 0 so this means...

I have been asked to determine the "shock regime" of a oblique shock / bow shock interaction based on the angle of the impinging shock and flow conditions. What does this mean? My initial thoughts were that I was being asked to determine whether the shock was strong or weak, but since the...

Hi. In this video: he ignores the magnetic field from current 2(I2). Could anyone give me a good explanation why?

Recently it struck me that I'm not sure I understand the weak interaction at all. What causes it to happen? I know that its mediated by the W and Z bosons and has a short range as a result of the large mass these bosons posses, but what does that range refer to? Range from what?!

Could an energetic neutrino (of any flavor), on passing near an electron, nucleon, or nucleus, be stimulated to emit a neutrino pair (of any flavor)? An example might be an energetic electron-neutrino, passing close to a nucleus, and emitting a muon-neutrino/muon-antineutrino pair., with the...

If a symmetric distribution of charge has no electric dipole moment, where does the \mu term we write in the part of the hamiltonian representing interaction with light come from? We suppose it is induced by the electric field of the light?

Anyone can help me how to argue that interaction lagrangian is invariant under gauge transformation?

Homework Statement Consider two spin 1/2 particles interacting through a dipole-dipole potential \hat{V} = A\frac{(\hat{\sigma_1} \cdot \hat{\sigma_2})r^2 - (\sigma_1 \cdot \vec{r})(\sigma_2 \cdot \vec{r})}{r^5} If both spins are fixed at a distance d between each other, and at t = 0 one of...

I have personally been deeply fascinated by the processes and principles that underlie the QED and have done some recent research myself. However, recently my teacher posted me a question that stunned me. He went,"Why do like charges repel and unlike attract?" In QED I understand that this is...

Homework Statement This is not homework but relevant to an interaction model that I am developing. I assume an even distribution of sources on a spherical 3d-hypersurface, the sources having a potential as a function of pairwise 4-distance between any two sources. I wish to obtain the sum...

Homework Statement A 0.62-kg basketball dropped on a hardwood floor rises back up to 64% of its original height. If the basketball is dropped from a height of 1.6m , how much energy is dissipated in the first bounce? How much energy is dissipated in the fourth bounce? Homework Equations U(x) =...

Homework Statement Hey guys! I'm not convinced by what I obtained so far, please tell me whether I'm in the right or wrong direction. The Hamiltonian has the form ##H=-h\sum _i s_i## where ##s_i=\pm 1## and ##h=kT##. 1)Calculate the partition function and the Gibbs free energy. 2)Calculate the...

Can you look at an interaction term in your lagrangian or hamiltonian, like L_{\rm int} or H_{\rm int}, and say immediately how its diagrams will diverge (as in quartic, quadratic, linear, log, etc.)?

Homework Statement Thin rod of the length l is placed with one of its ends placed at the center Oof the thin ring of radius R as shown, perpendicular to the plane of the ring. Rod is charged with total charge Q that is distributed along the rod’s length with the linear charge density...