What is Quantum chromodynamics: Definition and 20 Discussions

In theoretical physics, quantum chromodynamics (QCD) is the theory of the strong interaction between quarks and gluons, the fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type of quantum field theory called a non-abelian gauge theory, with symmetry group SU(3). The QCD analog of electric charge is a property called color. Gluons are the force carrier of the theory, just as photons are for the electromagnetic force in quantum electrodynamics. The theory is an important part of the Standard Model of particle physics. A large body of experimental evidence for QCD has been gathered over the years.
QCD exhibits three salient properties:

Color confinement. Due to the force between two color charges remaining constant as they are separated, the energy grows until a quark–antiquark pair is spontaneously produced, turning the initial hadron into a pair of hadrons instead of isolating a color charge. Although analytically unproven, color confinement is well established from lattice QCD calculations and decades of experiments.
Asymptotic freedom, a steady reduction in the strength of interactions between quarks and gluons as the energy scale of those interactions increases (and the corresponding length scale decreases). The asymptotic freedom of QCD was discovered in 1973 by David Gross and Frank Wilczek, and independently by David Politzer in the same year. For this work, all three shared the 2004 Nobel Prize in Physics.
Chiral symmetry breaking, the spontaneous symmetry breaking of an important global symmetry of quarks, detailed below, with the result of generating masses for hadrons far above the masses of the quarks, and making pseudoscalar mesons exceptionally light. Yoichiro Nambu was awarded the 2008 Nobel Prize in Physics for elucidating the phenomenon, a dozen years before the advent of QCD. Lattice simulations have confirmed all his generic predictions.

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  1. M

    Could there ever be a chromo-electric field weapon?

    In Star Trek, they mention a Chromo-electric pulse and Chromo-electric force field. I know chromo-electric fields hold the nuclear force together with gluons but could a highly advanced civilization use chromo-electric fields for weapons or protection?
  2. VVS2000

    Physics Choice of specialization for Quantum Chromodynamics PhD?

    I am entering into the 2nd year of my masters and I plan to do my phd in quantum chromodynamics. So for my specialization, would it be helpful if I choose nuclear and particle physics or quantum field theory?
  3. RicardoMP

    Feynman one-loop integral ##I_{21}##

    Starting from the general formula: $$I_{n,m}=\frac{1}{(4\pi)^2}\frac{\Gamma(m+2-\frac{\epsilon}{2})}{\Gamma(2-\frac{\epsilon}{2})\Gamma(n)}\frac{1}{\Delta^{n-m-2}}(\frac{4\pi M^2}{\Delta})^{\frac{\epsilon}{2}}\Gamma(n-m-2+\frac{\epsilon}{2})$$ I arrived to the following...
  4. RicardoMP

    A What Is the Renormalized Gluon Dressing Function?

    Consider, for example, the gluon propagator $$D^{\mu\nu}(q)=-\frac{i}{q^2+i\epsilon}[D(q^2)T^{\mu\nu}_q+\xi L^{\mu\nu}_q]$$ What exactly is the renormalized gluon dressing function ##D(q^2)## and what is its definition? My interest is in knowing if I can then write the bare version of this...
  5. RicardoMP

    A Trace of a product of Dirac Matrices in a Fermion loop

    I'm working out the quark loop diagram and I've drawn it as follows: where the greek letters are the Lorentz and Dirac indices for the gluon and quark respectively and the other letters are color indices. For this diagram I've written...
  6. T

    Axial Transformation of a pion

    Homework Statement I'm considering a non-linear chiral theory where the Lagrangian is in terms of the field #\Sigma = e^{\frac{2i\pi}{f}}# where #\pi# is my pion matrix containing pion, kaon, and #\eta#. I need to calculate the transformation of #\pi# up to order #\pi^2# under an axial...
  7. A

    A Is field theory needed in Regge-theory?

    I have been reading some papers from G.F. Chew and S. C. Frautschi and they do not even bother to introduce the concept of "Field" when they describe hadron interactions. My impression is that they do not need to because interactions seem to be described by single Regge-trajectories. However...
  8. YoungPhysicist

    Quantum Introduction to Quantum Chromodynamics: A Textbook

    Is there a good introduction textbook or pdf for quantum chromodynamics?
  9. Suppaman

    B Theories of Quantum Physics, do they exist?

    Every time I watch another YouTube video about the "spooky" stuff or multiple slit experiments they never have a proposed explanation of how they work. It would seem to me that if you had a proposed idea then people could think of experiments to prove or disprove the idea. But with no ideas it...
  10. Urs Schreiber

    Insights A First Idea of Quantum Field Theory - 20 Part Series - Comments

    Greg Bernhardt submitted a new PF Insights post A First Idea of Quantum Field Theory - 20 Part Series Continue reading the Original PF Insights Post.
  11. BiGyElLoWhAt

    I Why Plot Spin vs Mass^2 in Particle Physics?

    Maybe this is more quantum, but I'm not sure. I was watching Susskinds first String lecture on youtube, and he was talking about how, within each particle family, you get a straight line called a regge trajectory if you plot spin vs. mass^2. He also mentioned that there was some slight insight...
  12. Kyx

    I Understanding Quantum Chromodynamics: The Colorful World of Quarks Explained

    So, a particle made of quarks is only stable if the 'colours' of the quarks add up to white So, red + antired = white blue + antiblue = white green + antigreen = white red + blue + green = white red + antired + red + blue + green = white But what causes the 'colour'? And why do they have to...
  13. Alfie Simpson

    What is QCD (quantum chromodynamics)?

    Can someone give me a brief overview of QCD, I'd like to know famous physicists that worked in the field, the main theory's it includes, when did it begin and why do we study it? Thank you.
  14. Drakkith

    Quantum Chromodynamics Binding Energy

    Binding energy is typically used to talk about the amount of energy needed to separate bound particles. This means that it represents the energy lost when particles enter a bound state. So, why does this article use the term "binding energy" to talk about the energy/mass content of a proton...
  15. G

    Gluons relating to quantum chromodynamics

    I know gluons relating to quantum chromodynamics are the force that holds quarks or whole nuclei of the atom together, is it considered a particle, or since its a force,is it just representing something invisible, is it actually there, like quarks or protons and neutrons. The same with all bosons.
  16. seouldavid

    Lectures on Quantum Chromodynamics from CERN

    This contains many links to physics video lectures on quantum chromodynamics (QCD) from CERN - introduction to QCD, QCD and collider physics, QCD Phenomenology etc. http://www.infocobuild.com/education/audio-video-courses/physics/qcd-cern.html
  17. P

    Is a Year-Long Quantum Chromodynamics Class Worth the Exam Stress?

    If I had to teach a class on a year-long Quantum Chromodynamics I would give an exam about everything they should know in physics on the first day of class worth half of the grade for the rest of the quarter. That way I’d know that these FOOLS would know their STUFF and not be wasting my time! eb
  18. R

    Quantum Chromodynamics for QFT Students

    What is a good introductory book on Quantum Chromodynamics that assumes QFT as a prerequisite?
  19. P

    References for quantum chromodynamics

    Hey all, I am currently in a 300 level physics class, Concepts of Modern Physics, and as a semester project we are required to research a topic and do a presentation. I chose QCD because I have done some reading on it and it seemed the most interesting on the list. Although, i would like to...
  20. K

    Quantum chromodynamics and gravity

    A graviton is supposedly massless and has spin 2. But these characteristics of the graviton come from quantum mechanics in which it is assumed that the graviton does not interact with other force carrying particles.Is it possible that a graviton has a colour charge for example, and interacts...