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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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Gluons pions and the strong nuclear force

Within Baryons is the force holding them together purely gluons or are pions involved? Between protons and neutrons in a nuclei is it purely the exchange of pions between baryons which hold the ...
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How do we know that gluons have no electric charge?

Since the W boson carries electric charge and there is no a priori reason that massless electrically charged bosons cannot exist, I'm wondering if the lack of gluon electric charge has been confirmed ...
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Do gluons interact with each other by the strong foce?

I learned that strong force between quarks are mediated by gluons. What does this say about interactions between gluons? Do they interact with each other by the strong force?
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Why do quarks and gluons have colour?

I asked a question here a few days ago and got some fantastic answers so I'm going to continue. Let me preface this by saying I know quarks do not actually have 'colour', but colour is some sort of ...
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Comparison between $\rho^0$ and $J/\psi$ decay mode

Why must a hadronic decay of the $J/\psi$ meson include (at least) three gluons? Why is the decay mediated by a single gluon allowed for the $\rho^0$ meson?
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How to think about color charged objects

When imagining color charged objects, I know we can treat color and anti-color much like electromagnetism. What I'm having trouble with is imagining the interaction of similarly coloured objects. Now ...
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Does the external leg contraction of gluon in QCD carry group generator index?

While I am trying to compute the amplitude for the following Feynman diagram I realized that the external leg contraction of $g$ should carry group generator index $A$ or $B$, is that right? If so, ...
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How do we know that gluons travel at the speed of light?

Since gluons are located within nucleons and immediately outside of them, how do experiments determine parameters like their speed? Is it possible we could be assuming they travel at the speed of ...
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Question about Gluon self energy diagram/symmetry factor

I am a qft beginner and have a question: In Peskin & Schroeder chapter 16.5 there is given an expression for a gluon self energy diagram: According to the feynman rules we get $\frac{1}{2} \int \...
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Spin-helicity formalism for gluon-gluon amplitudes

In Schwarz's QFT he introduces in chapter 27 the Spin-Helicity formalism as a way of calculating gluon-gluon interactions much easier than going through all the Feynman calculus from the beginning to ...
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How do we show that gluon-fields have color?

I understand how to derive the QCD lagrangian based on certain assumptions about Quark fields and $SU(3)$ gauge invariance and in the final expression one finds the term $(A_µ)^c*T_c$ where $T_c$ is ...
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What is direct interaction, if exist, between gluons and pions?

Gluons mediate the strong force between quarks. Pions mediate the nuclear force or nucleon-nucleon interaction or residual strong force. I had thought of some scalar bosons for my idea because if I'm ...
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Conversion of gluons into hadrons

Why and how does a gluon become a hadron when it leaves a hadron? Is this an analogous process to the way a quark becomes a meson, when it is "forced" out of (let's say) a proton?
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Covariant Derivative in QCD: How does it act on gluons?

Let the covariant derivative be $$D_\mu = \partial_\mu + \text ig\ A_\mu^a t^a,\quad a=1,\ldots,8$$where $g$ is the bare QCD coupling, $A_\mu^a$ are the eight gluon fields and $t^a=\tfrac{1}{2}\lambda^...
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Do gluons decay?

I have seen examples of other particles that decay into gluons but do gluons themselves ever decay. Since gluons are not composed of anything else I assume they are fundamental. On there other hand ...
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Gluon field calculations [closed]

How do I calculate the qcd covariant derivative I can’t figure out the value of the gluon field I have tried many sites on the internet This equation shows the covariant derivative: $$ D_\mu = \...
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Can we find a free gluon?

I have read these questions: Quark intrinsic angular momentum and the Proton Spin Crisis About free quarks and confinement https://en.wikipedia.org/wiki/Gluon And it made me curious. I understand ...
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How can massless gluons interact with each other?

Massless particles, such as photons and gluons, move with the speed of light and consequently experience no time. According to Special Relativity, time stops at the speed of light. As a result, ...
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Do gluons move faster than light?

Gluons are massless so move at the speed of light. Gluons also are supposed to exchange gluons themselves. Wouldn't this require the gluons which are exchanged between gluons to move even faster than ...
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Importance of Glueball [closed]

In Wikipedia, "In particle physics, a glueball (also gluonium, gluon-ball) is a hypothetical composite particle.[1] It consists solely of gluon particles, without valence quarks. Such a state is ...
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How does mass of the exchange particles affect the range of a force? [duplicate]

I read an article asserting that nuclear force is a short range force because of gluon's mass, and EM force is a long range force because photons massless. I also want to know, why quantum ...
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What is the physical meaning of the Gell-Mann matrices generating SU(3)?

I understand on a surface level that there are these matrices that generate the group SU(3). However, when reading books on gauge theory they appear to make the jump from SU(3) having 8 generators to ...
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Does the field (force-carrying) of a gluon or boson have a magnetic-like shape? Not spherical

The challenge of force-carrying boson is that many experiments generate results that are not consistent. Hence, quantum statistics. It is established that things like 'strong nuclear interaction/...
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Quark-Gluon color relationship in pure QCD

Consider pure QCD, flavor turned off. There are 3 quarks and 3 anti-quarks given by the fundamental IRR of SU(3) and its conjugate rep. We associate the three colors and anti-colors with the three ...
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Can photons be converted to gluons

Is there any method we can use to convert a photon into a gluon, as they are similar in many respects. For instance, if we pass a $100\,{\rm keV}$ photon through a strong electric field, can this ...
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How do partons' spin/orbital angular momenta contribute fractionally to the nucleon spin structure?

Experimentally it is found that the spin and orbital angular momenta of quarks and gluons contribute fractionally to the total nucleon spin $1/2$, as in: $$\frac{1}{2} =\frac{1}{2} \Sigma_q + \...
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Do gluons have only two possible eigenvalues of helicity?

In the Standard Model, gluons are massless spin-1 bosons just as photons are, so it stands to reason that they only have two possible eigenvalues of helicity for the same reason that photons, which ...
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Why are gluons necessary?

I understand that quarks are attracted to each other when they have different color charges to become neutral. I also understand that gluons are the exchange particles of the strong force by switching ...
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Counting gluons in a proton, are we sure measurement doesn't affect the number?

Regarding gluons in a hadron, when you look with one resolution you see a certain number, but looking closer you see some of these particles have split. How are we actually looking at these? Can we be ...
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Why electron and positron annihilate would produce hadron (jet of gluon)?

Electron (fermion) is an elementary particle just like positron and they interact via boson which is photon, electromagnetic force. I like to know why is gluon (hadron) being emitted when electron and ...
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Gluon photon mixing — why not?

In the electroweak theory there is a mixing between forces which results in the photon being part weak and mostly electromagnetic and the Z0 being mostly weak and partly electromagnetic. Why doesn't ...
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Why do weak interactions exclude gluons?

Weak interactions seem the most universal after gravitation. A very few particles avoid them, only the photon and gluon, plus right leptons. The photon, however, is a part of the electroweak ...
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How to determine Gauge Boson charge?

Given the field strength: $$F^a_{\mu\nu} = \partial_\mu A^a_\nu - \partial_\nu A^a_\mu + g \; f^{abc} A^b_\mu A^c_\nu$$ We'd get interactions between three and four bosons, former one will look like:...
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Why are gluons believed to be massless?

Earlier questions under a similar title referred to the short range of the strong force. My question is completely different. I'd like to know why gluons are considered massless in the Standard Model (...
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Quark colour charge at gluon emission/absorption

Suppose I have a very simple QCD diagram, where a quark emits a gluon and continues on. Can I describe such process through "usual" quantum mechanics? More specifically, can I use the concept of ...
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Leading order DGLAP evolution

Consider the leading-order (LO) DGLAP ((Dokshitzer–Gribov–Lipatov–Altarelli–Parisi) equation $$x \mu^2 \frac{d xg(x,\mu^2)}{d\mu^2}= \alpha_s \int_x^1 dz P_{gg}(z) \frac{x}{z} g(\frac{x}{z}, \mu^2) + \...
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Do gluons have properties other than color charge that distinguish them from each other?

Gluons in quantum chromodynamics (QCD) come in eight color charge varieties. But, it has never been clear to me if they differ from each other in other respects the way that, for example, photons do. ...
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Strangeness and G-parity of glueballs

I know that glueballs are virtual particles predicted by QCD and that they form a color singlet. I am stucked in the problem, which seems to be a easy one, of finding the strangennes and G-parity of ...
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Since gluon fields do not appear apart from quarks, did gluon fields first appear during the quark epoch?

Big Bang cosmology and grand unification theories say that the strong force and the electroweak force separated during the electroweak epoch, i.e., $10^{-36}$ to $10^{-32}$ seconds after the Planck ...
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Quark chiral condensate v.s. gluon condensate

In Wikipedia, it says that "The evidence for QCD condensates comes from two eras, the pre-QCD era 1950–1973 and the post-QCD era, after 1974. The pre-QCD results established that the strong ...
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What is the ratio of gluons to baryons?

Gluons bond quarks into baryons (i.e., protons and neutrons). For example, two up quarks and one down quark form a proton while one up quark and two down quarks form a neutron. Is there one gluon per ...
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Can we observe “classical waves” produced by the weak and strong nuclear force bosons?

A real photon is wieved as an electromagnetic wave. In addition, if gravitons exist, we can view real gravitons as gravitational waves. However, can we observe the waves from the weak and strong ...
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How (or when) do gluons change the color of a quark?

I know a baryon is only stable when it contains a quark of each color. And as far as I know, the gluon essentially changes the color of a quark and moves onto the next, and this is what holds the ...
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Do electrons interact with gluons?

I know the straightforward answer to this question is no: electrons are leptons which by definition don't interact via the strong force, gluons are the mediators of the strong force and hence ...
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Where did all the negative potential energy in gluons went to?

I have watched PBS Space Time that gluons could be viewed as negative potential energy (tension between quarks) and that they actually are 99% of all the mass in protons and neutrons. Now the way I ...
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What's the difference between a meson and a glueball?

There is a blog post by Matt Strassler about the structure of hadrons. He contrasts the "conventional" picture of hadrons shown below: with one that he considers to be more accurate: From the ...
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What exactly is the color charge in QCD? [duplicate]

I don't have strong background in particle physics. Though, I had learnt a little of it. I have gone through the basic of these stuffs (pretty OK). If I have done my homework right, color charge (R,G,...
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Properties of the nucleons and the nucleus from the interactions between quarks and gluons

Is it possible to deduce the properties of the nucleus or that of the nucleons from the QCD interactions between the constituent quarks and gluons?
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Viable combinations of gluons interacting with colour singlet states

A proton-proton scattering event cannot take place with the exchange of a single gluon. The argument is that an attempt to draw a Feynman diagram for this process results in colourful outgoing states ...
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quark annihilation into two gluons

We're working through the Griffith's introduction to elementary particle physics and are wondering about the quark antiquark annihilation process. There are actually three first order processes, but ...