What is Gluon: Definition and 69 Discussions

A gluon () is an elementary particle that acts as the exchange particle (or gauge boson) for the strong force between quarks. It is analogous to the exchange of photons in the electromagnetic force between two charged particles. In layman's terms, they "glue" quarks together, forming hadrons such as protons and neutrons.
In technical terms, gluons are vector gauge bosons that mediate strong interactions of quarks in quantum chromodynamics (QCD). Gluons themselves carry the color charge of the strong interaction. This is unlike the photon, which mediates the electromagnetic interaction but lacks an electric charge. Gluons therefore participate in the strong interaction in addition to mediating it, making QCD significantly harder to analyze than quantum electrodynamics (QED).

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  1. Astronuc

    I Experiment finds gluon mass in the proton (?)

    Article published at Phys.org - Experiment finds gluon mass in the proton https://phys.org/news/2023-03-gluon-mass-proton.html An interesting diagram accompanies the article. Article in Nature (requires subscription or purchase, but one can read the abstract)...
  2. James1238765

    I Use of Gell-Mann matrices as the SU(3) basis for gluon states?

    The 8 gluon fields of SU(3) can be represented (generated) by the 8 Gel-Mann matrices: $$ \lambda_1 = \begin{bmatrix} 0 & 1 & 0 \\ 1 & 0 & 0 \\ 0 & 0 & 0 \end{bmatrix} , \lambda_2 = \begin{bmatrix} 0 & -i & 0 \\ i & 0 & 0 \\ 0 & 0 & 0 \end{bmatrix} , \lambda_3 = \begin{bmatrix} 1 & 0 & 0 \\ 0...
  3. J

    I What happens to a gluon that does not have enough energy to hadronize?

    A real gluon created from say, some particle annihilation or decay, should hadronize when in space correct? Well what if that gluon does not suffice in energy to form quarks? Does it become a glueball? That leads me into another question, why are glueballs theorized to have specific masses...
  4. S

    I What evidence supports the theory of gluon masslessness?

    Gluons are supposed to have precisely 0 rest mass. However, gluons are always colour confined into hadrons with binding energies of hundreds of MeV. How is gluons´ lack of rest mass proven? Presumably through some symmetries, or lack of some processes. Which kinds of asymmetries and processes...
  5. S

    B Why Photon & Gluon are Exceptions from Higgs Field

    The photon and the gluon in the Standard Model do not interact with the Higgs field and are hence massless and travel at the speed of light. Is there a simple explanation why these two elementary particles are the exceptions?
  6. M

    I Understanding Gluon Self-Interaction and Quark/Gluon Jet Differentiation

    Hello! Based on QCD we can have gluon self-interaction i.e. a vertex with 3 or 4 gluons. What were the experimental evidences by which the existence of these vertices was confirmed? Also, how does one differentiate between a quark and a gluon induced jet? Thank you!
  7. C

    I No "i" in the Triple gluon vertex Feynman Rule

    This is probably a simple question but puzzled me a little when trying to explain something to somebody. In all resources online and in most books I've seen, the triple gluon vertex has no overall 'i' factor while e.g. the four gluon vertex always does. The photon and gluon propagators as well...
  8. A

    Amplitude with Feynman diagrams and gluon propagators

    The term which is relevant for the calculus is: $$ \bar u(p) \gamma^\alpha \frac{1}{\displaystyle{\not}p+\not k} \gamma^\nu \frac{1}{\displaystyle{\not}p'-\not k} \gamma^\beta v(p') \frac{k_\alpha k_\beta}{k^2} $$ $$ \bar u(p) \displaystyle{\not}k \frac{1}{\displaystyle{\not}p+\not k}...
  9. M

    B Quark Gluon Plasma In the Presence of Charged Leptons?

    It is my understanding that a state of matter known as quark-gluon plasma has been produced artificially and studied in various labs. How is the presence of varying densities of charged leptons such as electrons thought to influence the behavior of any naturally occurring examples of quark gluon...
  10. Paul Colby

    I Gluon creation and annihilation operators

    Hi, When one quantizes EM the resulting gauge boson, the photon, ends up being its own antiparticle. From what I read of gluons, they have anti particles. I can follow how anti particles come about quantizing a complex-valued field like that for electrons. For the spin 1/2 case non-interacting...
  11. ohwilleke

    B How many gluons on average are there in a proton at once?

    A proton is made of quarks and gluons bound by the strong force in a confined system. Further, all protons are basically interchangeable parts for the purposes of this question. Each one is identical in all material respects. Scientists know a lot about gluon energy density in protons. We have...
  12. S

    B Do Gluons Emit Photons?

    I've been googling this and can't come up with a direct answer. Can a gluon emit a photon? I know. 1. All Standard Model particles with mass interact via the weak force. 2. All quarks and gluons interact via the strong force. 3. All quarks, charged leptons and massive weak force bosons emit...
  13. C

    I Charge conjugation properties of the gluon

    The intrinsic charge parity of a species is the ##\eta_C## defined in the equation $$\mathcal C |\psi \rangle = \eta_C |\psi \rangle $$ which can take on values ##\pm 1##. Since the gluon carries a colour charge, it is not an eigenstate of the C (charge conjugation) operator. 1) Why do I...
  14. C

    I Identifying gluon in Feynman diagram

    Consider the process in the picture below where an ##r \bar r## state goes to an ##r \bar r## state through mediation of a gluon. The gluon may carry the colour anticolour combination ##r \bar r##. I'm just wondering... 1) Can we have a gluon with the colour assignments just ##r \bar r##? If...
  15. C

    Adjoint transformation of gluon

    It is commonly written in the literature that due to it transforming in the adjoint representation of the gauge group, a gauge field is lie algebra valued and may be decomposed as ##A_{\mu} = A_{\mu}^a T^a##. For SU(3) the adjoint representation is 8 dimensional so objects transforming under...
  16. FallenApple

    I Why do quarks prefer to live on top of fluctuating gluon fields?

    So below is an animation of a quantum field's energy density fluctuating. Specifically, a gluon field. So the empty spots are not truly empty but where the field is at the lowest energy. I saw a video from veritasium stating that the quarks are likely to live on top of those lumps. Why...
  17. romsofia

    A Misunderstanding gluon saturation?

    After attending a seminar, a confusion arose. I attempted to ask the speaker the question, but it seems that my question may not be well posed, so I'll try here. As I understand it, gluon saturation are places we expect there to be gluons based on some transverse momentum after our...
  18. J

    A Gluon spin and quark confinement

    Gluons are spin 1 particles so the Strong Force can both attract and repulse. The constituent partons of a meson are a quark and an antiquark so they must carry a given color and its anticolor, respectively, in order that there is no net color carried by the parton. In that case, the force...
  19. baxishta

    B Gluon Color: Possessing 2 Eigenvalues & Relationship to Tao

    if "color" is one of the eigenvalues, how may a single gluon be in possession of 2 of them and still be unique? also, a 2-color gluon is reminiscent of a 2-color tao, no?
  20. A AM ARYA

    I How can Gluon travel at speed of light?

    How can Gluon travel at speed of light when it is bound inside a proton or neutron?
  21. K

    What would be the physics of a hypothetical gluon star?

    imagine a hypothetical star composed of gluon stars, color neutral on whole, consisting solely of gravitationally bound glueballs. what would be its expected physics ? i.e for the mass of the sun, what would its radius be? would it emit radiation and if so what spectrum? would it be stable or...
  22. N

    Gluon Mass: Does Spontaneous Symmetry Breaking Give Them Mass?

    I know gauge theory predicts gluons are massless. But under spontaneous symmetry breaking do they get a mass? If they are massless why is the strong force such short range? Is it because of quark confinement and asymptotic freedom? It seems like a paradox.
  23. A

    Why Mesons Can't Be Made of 2 Quarks Alone

    As far as I know a Baryon is made of three Quarks (eg uud, udd etc) and a Meson of two Quarks, a Quark/Antiquark pair. As I am not a student / scholar in Physics but very deeply interested in this field, I couldn't find any explanation, why a Meson is omly made up by a Quark/Antiquark pair. What...
  24. OdysseasTS

    Schools Beamline for schools, Greek Delegation

    Hey! So I found this ( http://home.web.cern.ch/about/updates/2014/11/beamline-schools-competition-2015-launches-today ) and my high school's physics teachers liked the concept! So I've created a team to participate in this years contest. We were thinking to do something relevant with antimatter...
  25. Feeble Wonk

    Graviton represented as a gluon pair

    I'm not a physicist, but I'm pathologically curious about such things. I've recently heard that there is a growing school of thought among theoretical physicists that the graviton (and resultant gravitational force) is actually just an extension of the strong force conveyed by a gluon pair. This...
  26. E

    Advice for gluon vertex textbook

    Hello everyone, i'm having a hard time trying to derive the three gluon vertex in QCD, using the generating functional. Could someone please suggest a reference where it is computed step by step? My teacher lecture notes are not clear, and basically I don't understand what he's doing. A very...
  27. L

    Cross Section: Quark-Gluon vs. Quark-Photon

    This isn't a homework problem. I am preparing for a particle physics exam and although I understand the theoretical side of field theory, I have little idea how to approach practical scattering questions like these. THE PROBLEM: Dark matter might be observed at the LHC with monojet and...
  28. F

    What Are the Best References for the Two-Loop Gluon Propagator?

    Does anybody know a good reference for the gluon propagator at two loop? I need it in Feynman gauge, but to have it in light-cone gauge as well is a plus. Preferably a paper, or a book that is common (i.e. easy to find in our university's library :-) ). Thanks!
  29. S

    Is there a blue-anti blue gluon?

    the only reason i am not sure about the existence of blue-anti blue gluons is because i have never seen them in any of the explanations i have read or watched and that is what confuses me.
  30. C

    About the gluon feild and propagator

    I am confused about the very step from Eq.(14) to Eq.(15) in the paper http://arxiv.org/pdf/hep-ph/0308157.pdf There is one ##ig## in (14), while ##(ig)^2## in (15), where does it come from? Regards!
  31. Spinnor

    Feynman diagram for gluon exchange, time up, gluon horizontal.

    Consider the Feynman diagram below from, http://hyperphysics.phy-astr.gsu.edu/hbase/particles/expar.html where I assume time runs upwards and the gluon in the graphic runs horizontal and is labled as a green_antiblue gluon. If the gluon runs horizontal can one still label a gluon as being...
  32. O

    Are gluon lines drawn in opposite directions the same in Feynman diagrams?

    I draw Feynman diagrams in JaxoDraw. But If I draw gluon line up to down or down to up, I get different results for gluon lines. I share a picture to explain my problem. Are these two diagrams the same? http://img809.imageshack.us/img809/3184/rq9z.jpg
  33. H

    Hadrons rest mass comes from gluon field?

    I am confused on an issue relating to gluons and mass. As I understand it, quarks don't actually have a lot of rest mass. In fact, most of the rest mass found in Hadrons arises from the interactions and energy of the Gluon field between quarks(??). This sounds like GR to me, meaning that the...
  34. J

    Whatever happened to AdS/CFT and the Quark Gluon Plasma?

    Nice posting by Bee Hossenfelder on her Blog !.. http://backreaction.blogspot.nl/2013/09/whatever-happened-to-adscft-and-quark.html A decade ago, the AdS/CFT correspondence was celebrated as a possible description of the quark gluon plasma. RHIC measurements of heavy ion collisions at that...
  35. T

    Red quark going to a red quark via an gluon emission

    Hi, I'm currently doing a course in particle physics at masters level and I have this problem: I know that having an red:anti-red gluon isn't possible as this produces an non-zero trace for its representation, but if I have a red quark that emits a gluon and afterwards is still a red quark...
  36. P

    What happens to the gluon linking Quarks at time of formation of quark

    what happens to the gluon linking Quarks at time of formation of quark star? whether the quark star consists of only quarks or quark gluon plasma?
  37. G

    How does a gluon hold quarks together

    Here is a quote from Susskind's the Cosmic Landscape: I'm having a very difficult time wrapping my head around this. I'm pessimistic that it can be explained how gluon's hold quarks together because in order to explain x you need to break x down into parts and as of yet we do not know of...
  38. O

    Understanding Gluon Octet Mixing: Calculating Probabilities and Color Charges

    Hi, it's my first post :) I've been working on a learning app about subatomic particles for some time, and now we'd need to represent gluons. I want to do this correctly by representing the eight possible gluons in the octet, but don't really know how to read the name of a gluon. I know...
  39. maverick280857

    Gluon Scattering - Colored Feynman Rules for Yang Mills Theory

    Hi, I'm reading Appendix 1 of Section N2 (Gluon Scattering) in "Quantum Field Theory in a Nutshell" by Anthony Zee. The generators for SU(N) have the usual algebra [T^a, T^b] = i \epsilon^{a b c}T^c Suppose we adopt the following normalization \text{tr}(T^a T^b) = \frac{1}{2}\delta^{a b}...
  40. M

    Exploring the Gluon Octet: States and Equations

    Below are 2 states in the gluon octet. What is the difference between: and What do these equations represent?
  41. E

    Why gluon cannot decay to quark and photon

    What are flavor arguments that prevent a gluon from decaying into quark and photon, or anti-quark and photon, etc?
  42. P

    Conformal invariance of gluon amplitudes

    Hi, I'm very ashamed to not understand how even the simplest gluon amplitudes are conformally invariant. See eg http://arxiv.org/abs/hep-th/0312171 pages 11-12. M(1^-,2^-,3^+)=\delta(\sum_i \lambda_i\tilde{\lambda}_i)\frac{\langle12\rangle^4}{\langle12\rangle \langle...
  43. S

    Color of gluon mediating quark-antiquark process?

    I have the following process: q(R) + \bar{q}(\bar{B}) \rightarrow q(R)+\bar{q}(\bar{B}) In words: a quark with red color-charge and an antiquark with an anti-blue color-charge are incoming, and a red quark and anti-blue antiquark are emerging. Since I am not sure how else to draw that, I try...
  44. S

    Strong Force alternative theory besides gluon

    Hi I am just a newb with interest in physics. Maybe someone can help me out: Is there any theory that explains the strong force or bonding together of protons and neutrons in the center of the atom with a vortex in the center of the atom similar to a black holes vortex. And theorizes that...
  45. Z

    If the singlet gluon existed (and I realize it doesn't)

    OK, here's a question that's unusual in that it regards a particle state that's pretty much taken to be nonexistent. Nonetheless, my curiosity is piqued. I've read from multiple sources that if the singlet gluon existed, it would couple with equal strength to all baryons because they are also...
  46. A

    Color of Gluon Jets in Electron-Positron Annihilation

    What is the color of gluon (or gluon jets) predicted according to QCD? Here, I am talking about electron-positron annihilation that may cause gluon jets.
  47. M

    Color conservation in gluon fragmentation

    Hi, When a gluon fragments to a quark anti-quark pair (c c_bar for an example), how is color conserved? Gluon is colored but c c_bar pair is colorless. Thanks.
  48. Z

    Does gluon oscillation violate color conservation?

    Since the actual mass-eigenstate gluons are not the simple red-antired, red-antigreen, etc. but rather linear combinations thereof, is color charge still absolutely conserved? It seems that if we (perhaps naïvely) treat a gluon as simply fluctuating from one of the color-anticolor combinations...
  49. T

    QCD gluon propagator in axial gauge, polarization sum

    Hi! I have a process with multiple feynman diagrams where gluon propagators occur. When I use an axial gauge for the gluon propagator, do I have to use the same n-vector for every propagator? Following this I wonder whether I can use the same n-vector for every polarization sum in axial gauge...
  50. P

    Computing the 1-loop Correction to the 3 Gluon Vertex with Non-Zero Quark Mass

    Anyone know a reference in the literature that computes the correction to the 3 gluon vertex due to a quark loop with non-zero quark-mass?