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 ...

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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 ...
3
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1answer
51 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 ...
3
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0answers
36 views

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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0answers
17 views

The “force” of gravity is an illusion: things follow geodesics in space-time warped by mass-energy - can other forces be explained by similar models? [duplicate]

As I understand it, the force of gravity between two objects is not really a force, but appears to be so. It behaves in such a way that the Newtonian force explanation works in many cases, but the ...
2
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4answers
122 views

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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1answer
267 views

Lorentz invariance, energy-momentum conservation & the locality of interactions

I have been reading these notes ("Minkowski Spacetime: A Hundred Years Later", by Vesselin Petkov) 1, in which the author states (in the middle of the text on page 137) that "The only Lorentz ...
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0answers
27 views

What is meant by interactions being mediated by force-carrier particles?

When a photon interacts with an electron, what is observed to happen? Force-carrier particles are described as the mediators of these interactions. What does this mean and how is this concluded?
3
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2answers
99 views

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
24 views

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
54 views

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 $1/2$, $J_i$...
7
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1answer
331 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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1answer
58 views

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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4answers
3k views

Long/short-range interaction

A potential of the form $r^{-n}$ is often considered long-range, while one that decays exponentially is considered short-range. Is this characterization simply relative/conventional, or is there a ...
0
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1answer
30 views

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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0answers
30 views

Lagrangian Interaction Type and Spin-Dependence

So I'm transitioning from reading particle physics books to the literature, specifically as it pertains to dark matter models. In this case I'm talking about t-channel DM-nucleon scattering. They ...
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votes
2answers
51 views

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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0answers
54 views

Mystery $p^0$ particle

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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0answers
45 views

Quartic interactions of a complex scalar field

For a quartic self-interaction of a complex scalar field (matrix), one can write the terms: $aTr((\phi^*\phi)^2)$ and $bTr(\phi^*\phi)^2$ ; the trace and the "double" trace term, with two different ...
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1answer
26 views

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 ...
3
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0answers
21 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 & ...
0
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0answers
23 views

Elementary particles interaction time (in LHC, for example)

Feynman description of an interaction contains diagrams with different total time steps (that contribute only a little to the amplitude, I guess). Is there a calculation, for a given interaction, what ...
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0answers
35 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 ...
7
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4answers
253 views

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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0answers
38 views

Superficial degree of divergence for scalar theories

I have a few questions regarding the derivation of the degree of divergence for feynman diagrams. The result is $$D = [g_E] - \sum_{n=3}^{\infty} V_n [g_n]$$ (following notation in Srednicki, $P118$) ...
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1answer
81 views

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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1answer
100 views

Five-component field

Recently I was reading about 5-component field $(\varphi , \psi_{\mu})$, for which $$ \hat {p}^{\mu} \varphi = mc\psi^{\mu}, \quad \hat {p}_{\mu}\psi^{\mu} = mc\varphi . $$ This field refers to the ...
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0answers
50 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 ...
0
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0answers
78 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 ...
5
votes
1answer
133 views

Fifth force in string theory [closed]

I can't seem to get a clear description of what the "fifth force" in string theory is. What is the fifth force in string theory? What does it do? What mediates it?
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1answer
87 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 ...
8
votes
4answers
248 views

Is there some special case where a fermion can mediate a force?

Looking at the comments of this questions Does the gravitino contribute to the gravitational interaction? and even considering that the answers here in this other question Why are all force particles ...
2
votes
1answer
277 views

$G$-parity in an electromagnetic decay

I am looking at the decay $\eta\rightarrow\pi^+\pi^-\gamma$ and I would assume that the decay itself (ignoring the $\pi\pi$ final state interaction that is obviously strong) is electromagnetic since ...
5
votes
3answers
126 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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0answers
21 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
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1answer
50 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 ...
2
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1answer
51 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,...
1
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1answer
53 views

Can two photons form a bound state?

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 nevertheless have a gravitational mass, by which they can ...
1
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2answers
53 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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4answers
125 views

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 ...
0
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0answers
60 views

Friction forces on car wheel

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 ...
1
vote
1answer
104 views

Newton's third law at the quantum level? [closed]

let's look at force at the atomic level to understand the newtons third law of motion. I'll use Helium atoms as an example. Now imagine we start with one atom HE2 stationary, and throw another atom ...
1
vote
0answers
41 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 ...
6
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0answers
101 views

How do proteins perform their function? [closed]

Let's, for example, take a ribosome. It is an enzyme that is in turn just a molecule that must follow the laws of physics. Correct me if I'm wrong, but it can be looked upon as a molecular machine ...
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0answers
81 views

Question about interacting fields and feynman diagrams [closed]

The picture is taken from Chapter 4: 'Interacting Fields and Feynman Diagrams in An Introduction to Quantum Field Theory by Peskin and Schroeder. There is a two point correlation function $\left<0\...
1
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0answers
25 views

How can a net force of 0 still lead to movement and how is movement possible with interaction pairs? [duplicate]

So I always thought of movement as interaction pairs. For example, I thought that a rocket moves by applying a force of hot exhaust gases, which then apply a reaction force back on the rocket ...
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6answers
9k views

Why is gravitation force always attractive?

Why is the gravitational force always attractive? Is there another way to explain this without the curvature of space time? PS: If the simple answer to this question is that mass makes space-time ...
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0answers
80 views

Propagator with derivative interaction

I work with this interaction Lagrangian density $$\mathcal{L}_{int} = \mathcal{L}_{int}^{(1)} + \mathcal{L}_{int}^{(2)} + {\mathcal{L}_{int}^{(2)}}^\dagger = ia\bar{\Psi}\gamma^\mu\Psi Z_\mu +ib(\phi^...
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0answers
46 views

Generating functional for free and interacting theories [closed]

I'm asking probably a stupid question. We define the generating functional for free theories as $$ Z_0[J] = \int D \psi e^{i\int d^4x \left[ L_0(x) + J_l(x)\psi^l(x) \right]} $$ with $L_0$ the free ...
3
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2answers
132 views

How is dark matter detected?

What methods do we use to detect Dark Matter? If I understand correctly, due to lack of electromagnetic interaction it should be able to phase through normal matter nearly like through void - since ...
0
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1answer
37 views

Interaction Hamiltonian and shifts

When we quantize a free field theory, we set $\phi(x)$ to be the operators and we take the Fourier transform to determine the creation and annihilation operators $a_\omega,a^\dagger_\omega$ such that $...