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.
http://arxiv.org/abs/0804.3210
Introduction to String Theory and Gauge/Gravity duality for students in QCD and QGP phenomenology
Authors: Robi Peschanski (Saclay)
(Submitted on 20 Apr 2008)
Abstract: String theory has been initially derived from motivations coming from strong interaction...
Hi,
As you knew "Asymp. freedom in QCD" did explain th strong interactions...
I want anyone to simplify this theory and show that:
why g factor above 1?
and
Is Feynman rules still work for strong interactions, I mean as it successfully interpret QED interactions?
Thanks in advance
I have been working in the properties of the large gauge transformation of QCD in the temporal gauge and I have shown that these satisfy U_{n}U_{m} and commutes with the translations where the large gauge transformations U_n and U_m belongs to the homotopy classes characterized by winding...
Homework Statement
I'm doing a dissertation on heavy ion collisions and one of the things they look for in the collisions is chiral symmetry resolution - what is it?
Homework Equations
The Attempt at a Solution
I understand that it is a type of symmetry that is usually broken...
Which is the connection between the perimeter law for Wilson loops and quantum fluctuations of matter fields (presenting in the QCD Lagrangian); and why quantum fluctuations of gauge (Yang-Mills, gluonic) fields infolve the area law for appropriate Wilson loops? Senk You. Leonid.
I find it awkward that quarks are in fundamental representation of SU(3) while gluons are in adjoint representation of SU(3). Is there a reason as to why this is the case? Why aren't they in the same representation or in the current specific representation?
Hi, I was wondering, what does the realm of quantum mechanics cover? I mean, I always hear a talk about how it would be a holy grail of physics if we could somehow combine GR and QM. But what about QCD, QED, and other theories. Why aren't they mentioned? Is it because QM encompasses them?
CarlB called attention to this paper by Johan Hanssen: http://arxiv.org/abs/hep-ph/0011060, on the BTSM forum. Hanssen asserts that because the Lagrangian of QCD is nonlinear, since the structure constants for su(3) do not vanish, therefore you can't do Fourier transforms on the fields, and...
What is the relationship between pQCD and NRQCD?
Is it that pQCD is for high energy/short-distance regime, e.g. quark gluon plasma? And NRQCD is for low energy/long-distance regime, e.g. quarkonium ?
And what is relation between heavy quark effective theory and pQCD and that between heavy...
i am encoutering a problem
i use helicity method to caculate six photon amplitude in scalar QED but i don't know explicit form of wave fuction QED . And i need a book with title
" R. Gastmans, Ubiquitous photon: Helicity method for QED and QCD"
where can i find it?
thank you
In modify minimal subtract sheme,using dimension regulation, I calculate the
the renormalization constant of massive quark and massless quark,get the same result.But in some papers,they are different.
Is there a review or any book on MS renormalization,that giving all the self energy and...
Has there ever been/is there a project for lattice QCD which uses idle home PCs to assist in QCD calculations, similar to SETI@home?
Just wondering as it seems like the kind of project that is perfectly suited to the @home structure.
Why is QCD non-perturbative at low energies?
In QCD isn't the expansion parameter the fine structure constant?
\alpha_s \approx \frac{1}{137}
Does this somehow depend on energy, which wouldn't make sense to me. I cannot seem to find a good answer anywhere, so I thought I would ask here...
Why can people learn about QED and QCD and not about:QGD(i.e.Quantum gravitodynamics)?What are then the difficulties (both physically and mathematically speaking)that prevented theoretical physicists to develop such a theory??