Published online by Cambridge University Press: 05 November 2009
We introduce here quarks and gluons. The analogy with electrodynamics at short distances disappears at larger distances with the emergence of the string tension, the force that confines the quarks and gluons permanently into bound states called hadrons.
Subsequently we introduce the simplest relativistic field theory, the classical scalar field.
QED, QCD, and confinement
Quantum electrodynamics (QED) is the quantum theory of photons (γ) and charged particles such as electrons (e±), muons (μ±), protons (p), pions (π±), etc. Typical phenomena that can be described by perturbation theory are Compton scattering (γ + e– → γ + e–), and pair annihilation/production such as e+ + e– → μ+ + μ–. Examples of non-perturbative phenomena are the formation of atoms and molecules. The expansion parameter of perturbation theory is the fine-structure constant α = e2/4π.
Quantum chromodynamics (QCD) is the quantum theory of quarks (q) and gluons (g). The quarks u, d, c, s, t and b (‘up’, ‘down’, ‘charm’, ‘strange’, ‘top’ and ‘bottom’) are analogous to the charged leptons νe, e, νμ, μ, ν, and. In addition to electric charge they also carry ‘color charges’, which are the sources of the gluon fields. The gluons are analogous to photons, except that they are self-interacting because they also carry color charges. The strength of these interactions is measured by αs = g2/4π (alpha strong), with g analogous to the electromagnetic charge e.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.