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Questions tagged [gluons]

Gluons are vector gauge bosons that mediate strong interactions of quarks and themselves in quantum chromodynamics. There are eight of them, as they are in the adjoint representation of the SU(3) color group, and carry the color charge of the strong force, which results into the binding of hadrons.

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Why do protons not show a "classical" mass defect?

An atomic nucleus consists of protons and neutrons, held together by the strong nuclear force (i.e. gluons). The heavier a nucleus gets, the more neutrons have to be added to overcome the increasing ...
enzo's user avatar
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Yang-Mills mass gap caused by gluonballs or because dark matter WIMPs?

Yang-Mills quantum field theory predicts the existence of the lightest massive Bosonic (i.e. integer spin) particle. This massive Boson will be much lighter than the $W$ and $Z$ Boson and therefore ...
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Why so much kinetic energy inside a proton?

I'm reading 'Waves in an impossible sea' by Matt Strassler - a very good, popular science book, by the way - and he explains that the rest mass of a proton mostly comes from the kinetic energy of the ...
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How are $\pi$ Mesons Created in the Residual Strong Interaction?

Watching this episode of PBS Space Time, they run an animation of how pi mesons are exchanged by nucleons as the residual strong interaction to overcome proton electromagnetic repulsion. https://youtu....
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Does most of the Universe's mass come from pions (or 'virtual' pions) rather than gluons and quarks?

After the discovery of the Higgs boson, we were all told that most of a proton's or neutron's mass does not actually come from their three main ('valence') quarks and their interaction with the Higgs, ...
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Why are two gluons needed for Feynman diagram?

Why do we need two gluons for the decay $$\pi^-+ p\rightarrow\pi^-+n+\pi^+\:\:?$$ If we have always the gluon $$\frac{1}{\sqrt{2}}(r\bar{r}-g\bar{g})$$ it should be possible with only one gluon ...
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Energy of "free" gluon

Does exist, if it make sense, a formula to describe the energy of a gluon, since its creation to its absorption, like the formula of Planck for the photon $\hbar\nu$?
Vilnius's user avatar
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How exactly does the strong interaction decrease with distance?

So, we all know that the strong force asymptotes but the thing is I've never gotten a good description as to why Can someone explain; How the Strong force weakens with distance? I think I have got ...
Mike Mutethia's user avatar
3 votes
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No gluon interaction between nucleons

Given the spatial overlap of nucleon wave functions within the nucleus, why is the bonding of nucleons only the result of pion exchange and not of gluon interactions between quarks in different ...
Paul Weinreb's user avatar
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Why does the Yukawa potential fail for the strong force? [duplicate]

The gluon is a massless particle, so according to the Yukawa potential the strong force should have a $r^{-1}$ potential. However, that is clearly not the case. Is it because the gluons themselves can ...
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What is a polarized/unpolarized parton?

In QCD physics, certain partonic distributions like Generalized Parton Distributions (GPDs) and Transverse Momentum Distributions (TMDs) are defined for the case where the parton is either unpolarized,...
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Why are gluons massless as their range is finite?

The range of electromagnetic waves and gravitational force is infinity and the particles exchanged during these interactions are photons and gravitons respectively. Both are massless following the ...
Vanshika Dhiman's user avatar
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Justifying the identification of eight gluons with the ${\bf 8}$ from ${\bf 3}\otimes{\bf 3}^*$

When we combine the fundamental ${\bf 3}$ and antifundamental ${\bf 3}^*$ of color $SU(3)$ of QCD i.e. single quark of three colors and a single antiquark of 3 anticolors, nine states are obtained. ...
Solidification's user avatar
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Spin and rotation of gluon field components

The gluon field has 4 spacetime components: $A_\mu = (A_0, A_1, A_2, A_3)$, like the electromagnetic field. Firstly, how to find each component of the gluon field? And how to perform a rotation on ...
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Gluon scattering in AdS

In recent years there has been interest in computing scattering amplitudes of (super)gluons in Anti-de Sitter (AdS) space in all kinds of stringy theories in different spacetime dimensions (see for ...
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How do we measure the gluon scattering?

In QFT, we often calculate the 'Feynman amplitude' for gluon scattering. As we know, Gluon is gauge boson mediating the strong force between quarks. By color confinement, Quarks are never seen in our ...
Sasha Shin's user avatar
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Why is gluon massless from GUT point of view?

For not violating the gauge invarinace, of course, the gluon is massless. In respect of Spontaneous Symmetry breaking(SSB), however, I wonder why the gluon is massless, compared the $W^+$, $W^-$, $Z$ ...
Sasha Shin's user avatar
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If massless objects ALWAYS travel at the speed of light and gluons are massless, how are they trapped within hadrons without a need for event horizon?

From what I heard, unless we have some kind of other influence, all things and light move at the straight lines in spacetime. If they have a mass, then they can never reach the speed of light, but all ...
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Why do gluon jets have more particles?

From papers on the concept of quark/gluon jet tagging, I've seen that gluon jets have more particles and a broader radiation pattern. Why does carrying more color charge allow them to produce more ...
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What happens inside a proton?

This post contains 3 questions but they are very similar. I saw from this question What's inside a proton? and other websites that protons aren't really made up of three quarks, but a lot of ...
User9387425's user avatar
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What gives rise to mass gap for gluons, even if they are massless?

It is known that QED does not have a mass gap. On the other hand, at the heuristic level, QCD has a mass gap. But photons and gluons are both "massless". Could anyone explain (at least at ...
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Is there an energy release from gluon expansion and contraction?

When an electron drops to a lower orbit, energy is released as a photon. Gluons expand and contract in-between quarks, described like springs or rubber bands that have tremendous force when extended ...
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Glue vs spring, the approach

Why does quantum mechanics use the term "glue" instead of "spring"? Is the strong force wchich keeps quarks together so different from the behavior of springs that they must have a ...
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Are glueballs confined without a connection to quarks?

Without being bound to quarks through the strong force, is there any reason why glue balls would be confined? Are they confined
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How to determine where a gluon should be emitted in a Feynman diagram?

I have been learning how to draw Feynman diagrams for various decays. I just came across an interesting video where they draw the following diagram for $K^+ \to 2\pi^++\pi^-$: My question is as ...
WaterDrop's user avatar
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Understanding depiction of gluons in the nuclear force Feynman diagram

In this Feynman diagram for the nuclear force, it labels this exchange as a pion. However, I was under the impression that this force was mediated by gluons. In the caption for this picture, it says ...
Relativisticcucumber's user avatar
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Are gluon particles analogous to flux tubes?

I've always been told gluons are the force "particles" mediating the strong force. And I've learned that Fluxtubes are what hold quarks together. Are these fluxtubes the "particle" ...
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Do gluons interact via virtual photons?

On a video on Youtube, I commented how a PBS Space Time episode helped me understand the speed of light by calling it the speed of causality. In response, I received the following comment: "Let'...
Curious Layman's user avatar
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Tadpole diagram in one-loop QCD gluon self-energy renormalization

I am trying to study QCD renormalization at 1-loop order. So, when I take into account the gluon self-energy corrections, the book I am studying from says that there are three diagrams who contribute ...
ar em's user avatar
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Does each vector in $su(3)$ represent a different kind/type of gluon (infinite kinds/types of gluons); or, are they all considered the same kind/type?

According to Does gluons have names?, it seems that there is no way to give names to gluons because they are not "always the same". So, it seems to imply that the same gluon can change its ...
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Why are glueballs or particles made entirely of gluons unstable?

I am wondering why glueballs or particles made entirely of gluons are unstable. What prompts them to decay because each individual gluon themselves are massless and only together are they massive. So ...
Roghan Arun's user avatar
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5 votes
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Why are gluons color charged but not photon? Could there be a charged EM force carriers like gluons or neutral color charge carrier like photon?

Gluons have a color charge why don't photons have an electric charge like gluons?
unknow unknown's user avatar
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Do pions not interact with other pions via the strong force?

Imagine a positive and negative pion, their only interaction between each other would be due to electromagnetism and the weak force, right? It is not like these two pions can form neutral pions due to ...
Aravind Karthigeyan's user avatar
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Is the gluon also a repulsive force?

In the picture of a proton we see 3 quarks, held together by gluons. But the two $u$ quarks repel each other , so the gluons act through the strong force, whereas the $u$ and $d$ quarks attract each ...
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Does Yang-Mills have free gauge bosons?

Is there any physical problem with a propagating non-Abelian gauge boson? That is, a plane wave mode $A_\alpha^\mu e^{ikx}$, where $A_\alpha^\mu=b_\alpha\epsilon^\mu$, with $b_\alpha$ a constant ...
Ahron Maline's user avatar
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How do we know that the gluon travels at $c$? [duplicate]

How do we know gluons travel at the speed of light? can this be derived or is it just an assumption based on the similarity to photons?
Don Yost's user avatar
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Is the concept of bicolored gluons mathematically precise/meaningful? Please explain

Each flavour of quark carries a colour quantum number: red, green or blue. I know what it means mathematically. But elementary textbooks (e.g, particle physics by Griffiths) also say that gluons are ...
Solidification's user avatar
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1 answer
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Is sub-atomic particles (quarks) bunch of compressed photons? [closed]

According to theoretical physics,protons,neutrons and electrons are made up of sub particles called quarks which are the building block of matter (baryons). what if the quarks are bunch of compressed ...
Abel's user avatar
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Feynman diagram

In this picture first diagram, can't the gluon be a $Z$ boson? Similarly, can't the $Z$ boson in the second diagram be a gluon?
lalala's user avatar
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A gluon can have nine independent, bicolored states. How are some of the additions of these individual states, like $r\bar{r}+g\bar{g}+b\bar{b}$?

This came from the 25th page of the following pdf: http://www.gammaexplorer.com/wp-content/uploads/2014/03/Quarks-and-Leptons-An-Introductory-Course-in-Modern-Particle-Physics.pdf Sorry if I am asking ...
Coopthecomposer's user avatar
1 vote
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Has the quadruple gluon vertex of QCD been observed experimentally?

QCD has triple and quadruple gluon vertices in Feynman diagrams. Has the quadruple gluon vertex been observed? For example, did jet events confirm it? Or did some other experiments see evidence for ...
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1 answer
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Can a gluon split into three gluons: $g \rightarrow ggg$? (four gluon vertex)

I know $gg \rightarrow gg$ is possible, but is $g \rightarrow ggg$ possible? I don't see this anywhere although I think you could conserve colour charge (e.g. $r\bar{g} \rightarrow r\bar{g} + g\bar{b}...
nemo's user avatar
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Is $SU(3)$ (and not $U(3)$) the symmetry group of color interactions because $U(1)$ is already used for EM?

I have already seen this question. It was answered that $U(3)$ can be decomposed into $SU(3) \times U(1)$, and $U(1)$ is already used for the EM interaction. Still, I wonder why the EM interaction ...
MatterGauge's user avatar
7 votes
1 answer
976 views

Do gluons care about flavor?

I think the answer to my question is no, but I can't find an explicit statement about this on my books or online. I know that gluons are the vector bosons for QCD, the $SU(3)$ gauge theory of color, ...
Mauro Giliberti's user avatar
9 votes
3 answers
1k views

Is it possible for an isolated quark to exist if it's bound to one or more non-virtual gluons to render the system color neutral?

We know color-neutral bound systems of quarks exist in the form of hadrons, we suspect color-neutral bound systems of gluons exist in the form of glueballs, we have a candidate particle which may be ...
Adam Lincoln Steele's user avatar
1 vote
0 answers
87 views

If gluons can make other gluons, why don't they keep multiplying into infinity?

This video from Physics Videos by Eugene Khutoryansky says that since gluons have color charge, they can attract each other by making more gluons, and this is why the strong force doesn't behave like ...
zucculent's user avatar
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3 votes
1 answer
679 views

Number of gluons inside a proton/neutron

In the model of constituent quarks, of course very different of the picture of QFT about what a QCD proton/neutron is, protons are made of 3 quarks. However, how many gluons are inside a proton? After ...
riemannium's user avatar
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Do gluons mediate the interactions between different flavors of quark?

From some of the quite professional sources (Basics from QCD by CERN; QCD from PDG), the QCD lagrangian is written in the form of $$ L = \Sigma_{f} \; \bar{\psi}^{(f)} i \gamma^\mu D_\mu \psi^{(f)} + ...
王凯越 Kaiyue Wang's user avatar
2 votes
1 answer
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How is the colour quantum number not conserved in this process?

I stumbled upon this CERN article, where I found this diagram describing the process $gg \rightarrow HH$: I'm still new to QCD, and I don't see how a coloured gluon can decay into colourless final ...
Physicist_285's user avatar
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Can the process gluon + gluon $\rightarrow$ 2 Higgs proceed in the following way in the standard model?

At order $g_s^2$, usually only a triangle quark loop and box diagram are considered, I was wondering, is there some reason that excludes these diagrams from the possible standard model channels?
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