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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.

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128 views

Why is it that the interacting fields cannot be decomposed into Fourier modes like free fields?

In quantum field theory, a free scalar field can be decomposed into Fourier modes. But why is that, an interacting field cannot have Fourier decomposition? Can we not decompose any arbitrary ...
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Does spin state matters during interaction?

I'm asking whether the interaction between a pair of spin-up or spin-down electrons be any different from the interaction between a pair of electrons that comprises of opposite spin state? I think ...
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134 views

Higgs Coupling - Fifth Force [duplicate]

To which of the four forces of nature does the coupling of the Higgs scalar field to other quantum fields ultimately belong to, if any? If it doesn't fall into any of the four known categories of ...
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1answer
124 views

Is it a coincidence that there are 4 fundamental interactions and 4 quantum numbers? [closed]

I can imagine that a system where each component has four defining characteristics would also have four ways those components can interact; the characteristics define interaction for each group. I ...
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3answers
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How neutrons interact if not through an electromagnetic interaction?

According to the question Do positively charged particles exchange photons? there was an answer Yes. Photons are the carriers for the electromagnetic force, regardless of the charges involved. ...
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1answer
61 views

Interaction in spin models

In the Heisenberg Spin model, the spin components of spins in the same direction at different lattice sites couple together. Is there a physical scenario where, say, the $x$ Spin component of a spin ...
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4answers
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What is the “truth” of the electrostatic force?

I want to ask a question about the Coulomb force or the electrostatic force. As you can see, there are these statements: 1) The electric force is a "vector quantity". 2) The electric force between ...
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Can similar charges attract each other?

Yesterday my teacher was giving us an introduction to the fundamental forces of nature. She asked why opposite charges attract to each other and similar charges repel each other. This question gave me ...
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1answer
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What's the significance of a dimensionless coupling constant?

In the preface to Mark Srednicki's QFT book (an online draft version can be found here http://web.physics.ucsb.edu/~mark/qft.html), Mark mentions that the $\phi^3$ theory in 6 dimensions would be a ...
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$\phi^{n}$ quantum scalar field theories where $n$ is not an integer

Consider a quantum scalar field theory with interaction terms of the form $\phi^{n}$, where $n$ is not an integer. Where are some examples of widely-studied quantum field theories which involve such ...
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Does the Higgs field correspond to a “fifth” fundamental force? [duplicate]

I am pretty much a layman regarding particle physics. Reading popular accounts on the Higgs particle and the Higgs field, which supposedly explains (all?) the masses of the elementary particles by ...
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3answers
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How can Pauli's exclusion principle originate forces?

Recently I've seem two situation in which the Pauli exclusion principle is said to originate forces. The first was a derivation of the Lennard-Jones potential in the context of Solid State Physics ...
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1answer
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Feynman diagram representation of variational derivative of S-matrix

For quite some time I am struggling to understand section 6.4 in Weinberg volume 1. He observes there that if interaction hamiltonian density is extended by coupling to c-number fields $\epsilon$, $$ \...
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About the notion of the self-interaction of a field

In QFT it's very common to hear (read) about the self-interactions of a field. e.g. there's the self-interaction terms of the Higgs field, that come with $\lambda^3$ and $\lambda^4$, right? But I ...
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180 views

Is it possible that there is a 5th force or is it proven that there is no other force?

I heard about in high energy the 4 fundamental forces can combine. They were not separated until $10^{-11}$ seconds after the big bang and as the univers gets cold, they begun to seperate. Is it ...
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1answer
280 views

Is virtual particle the same thing as force particle?

Is virtual particle the same thing as force particle? Which of the above categories do photon, graviton and gluon fall into? Virtual particle, force particle, or both?
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Do all four fundamental forces have effects on space time?

Since gravity, a fundamental force, takes effect through ripples in spacetime, do the other fundamental forces do the same? For example, since gravitational waves are ripples in space time, are ...
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1answer
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Forces: In what manner do they act on objects?

Newton's laws explain how the application of a force affect other objects. But, in what manner is this force applied? I know about contact forces and action at a distance forces, so my question is not ...
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2answers
475 views

What does a physical surface look like at a subatomic level?

At the macroscopic level, we are all quite familiar with the concept of a physical surface. From wikipedia: https://en.wikipedia.org/wiki/Surface_(topology) In mathematics, a surface is a ...
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If the strong nuclear force is stronger than electrostatic repulsion, why don't nuclei collapse into a point?

Today in class we were discussing the strong nuclear force, and our teacher was explaining about how the strong nuclear force counteracts the repulsion force between protons in a nucleus. When asked ...
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2answers
859 views

Sufficient conditions for a interaction to be classified as weak, strong, …?

Let us say I have been given the equation of a interaction/decay/etc. between particles: $$X+Y\rightarrow A+B$$ Are their any sufficient conditions that we can use to determine the type of interaction ...
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1answer
565 views

How do non-contact forces work?

One question has been bugging me ever since I started learning physics, the textbooks successfully describe the empirical observations but haven't given any reasoning behind it. What I want to ...
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0answers
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How do force carrying particles “give” force? [duplicate]

So, I am not taking physics in school, but I do have an interest in it, and I was wondering, in the standard model, all of the force carrying particles (photons, Z Bosons, W Bosons, gluons, and (...
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4answers
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How can fields interaction give rise to particles?

We say light a matter-wave, meaning along with its wave property it shows particle nature. But how can fields interaction (electric and magnetic) give rise to particles (photon)? I wish someone could ...
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The meaning of 'coupling'?

In quantum mechanics if two quantities $A$ and $B$ are said to be coupled what does this actually mean? I would guess that it means we have a term like $A\cdot B$ in the Hamiltonian but this is only ...
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1answer
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Why can the 2p0 to 1s transition in hydrogen with dipole interaction not be solved without splitting into x,y,z polarisation?

The $2p_0$ and $1s$ wavefunctions for hydrogen; $ \psi_{2p_0} = \dfrac{1}{4\sqrt{2\pi}} \left(\dfrac{Z}{a_b}\right)^{\frac{3}{2}} \dfrac{Z r}{a_b} e^{\frac{-Zr}{2a_b}} \cos(\theta) $ $ \psi_{1s} = ...
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1answer
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Angular momentum in annihilation $n\overline{n} \rightarrow \pi^0 \pi^0$

Consider the annihilation of a neutron by an anti-neutron $$ n\overline{n} \rightarrow \pi^0 \pi^0 $$ so that the initial relative angular momentum is zero. Because the spin of neutrons is $1/2$, $J_i$...
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1answer
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Is it possible the weak force isn´t fundamental? [closed]

Once the strong force was thought to be a fundamental force mediated by the massive pion. Later colour and gluons were introduced. The old strong force was a residue force of the new fundamental force....
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How can I determine the interaction knowing the decay formula?

I know the kind of interaction occurring in very common reaction. For example, I know that the interaction: $e^- + e^+ \longrightarrow \mu^+ + \mu^-$ is driven by the electromagnetic force (there is ...
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Clarification of the concept of Boson Mediator and 'Mediation' in Physics? [closed]

I would like to have a clear concept of Higgs 'mediator' and that 'mediation' speak in physics, what you 'swap' a particle with ...
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1answer
301 views

Mystery $p^0$ particle [closed]

Some exercises in my physics book mention a particle denoted $p^0$, but I can't seem to find any information about this particle, neither in my book nor on the web. I've been able to deduce from the ...
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1answer
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why does the Lennard-Jones potential fail to accurately describe forces between simple molecules, eg ammonia?

I have found only one reason, this being polarisation isn't accounted for. See for example this PDF - it is in the middle of the second paragraph, first page. What other reasons lead to the failure ...
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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 & ...
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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 ...
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1answer
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Backing out of interactions: Does physics account for such a thing?

Does physics account for interactions between light and matter ever being "not completed" or backed out of? Here's what led me to the question. In learning about interference in light, I ended up ...
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0answers
490 views

Neutrino interaction probability [closed]

Just a quick question, if a single 1GeV neutrino (muon neutrino) were fired at a block of iron with a given density, $\rho$, and the neutrino-nucleon interaction cross section is $\sigma$, what would ...
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0answers
524 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 ...
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1answer
116 views

What would happen if there was a fifth fundamental force? [closed]

Preceding this question, as a student of physics, my knowledge of theoretical physics is somewhat limited. So I came across this article, which posited what the universe would be like if three ...
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4answers
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Why don't we call the fermions in the standard model force carriers?

Maybe this is a chicken-and-egg problem, but couldn't we call all the bosons fundamental and treat the fermions as force carriers between them? EDIT: After all we never see the asymptotic states of ...
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3answers
758 views

If neutrons aren't affected by electromagnetic force, what causes it to bounce off matter?

Say a neutron is heading for a mountain, what would cause it to bounce off said amalgamation of matter? Electromagnetism is ruled out, gravity is too weak, (if I'm not mistaken) nuclear strong force ...
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1answer
112 views

The charges of the forces

I am trying to establish a simplified understanding of the fundamental forces to explain them to a young audience. If we say that gravity has one charge (attractive), electromagnetism has two charges ...
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1answer
971 views

Why is there no fundamental force following from the $SU(4)$ symmetry?

I've understood that the three fundamental interactions described by the Standard Model (the electromagnetic, the weak and the strong force) are thought to correspond (roughly) to gauge invariances ...
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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 ...
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1answer
856 views

What is the relation between interaction range and the mass of gauge bosons?

I have just started to read spontaneous symmetry breaking, where it is mentioned that EM fields are infinite in range, so the gauge boson has to be massless, while for the strong and weak interactions,...
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1answer
220 views

Can two photons form a gravitational bound state? [duplicate]

I've always wondered if it's possible to bind two photons, in particular by gravitational interaction. Photons don't have a rest mass, but do nevertheless have a gravitational mass, by which they can ...
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2answers
129 views

Questions about particles and their forces

Consider the hypothetical scenario where 2 particles are headed for each other in a collision course but neither interact with a common force. Do these particles simply pass through each other?
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Why don't photons attract?

I was reading in Griffiths, Quantum mechanics 2nd Edition about the Exchange forces, so it says that identical bosons attract each other, like the case of Einstein Bose condensates, identical fermions ...
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0answers
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Friction forces on car wheel [duplicate]

I know that frictions means a lot for car wheel. I've been looking all around a lot and trying to figure all out. I have found out about Coefficient of friction depends on slip ratio(which I am still ...
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4answers
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What are “Force Carriers”?

The concept of "force carriers" is hard for me to understand. I can understand "energy carriers". I can understand mass x acceleration but I can't see how this applies. Does anyone have a ...
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Should 4 fundamental forces really be 3 because of electroweak unification?

I read @ http://www.particleadventure.org/ Physicists concluded that, in fact, the weak and electromagnetic forces have essentially equal strengths. This is because the strength of the interaction ...