Talk:Pion

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[edit] ToDo List

The following article enhancements should be dealt with at some point:

  1. pions mediate the nucleon-nucleon force.
  2. The Yukawa potential is a non-relativistic description for them,
  3. The relativistic equation for pions is the Klein-Gordon equation
  4. They are pseudoscalars under parity inversion,
  5. They couple to the axial vector current, the couple is the axial coupling constant which is a "fundamental"/"important" parameter of the nucleon.
  6. pion is part of the triplet representation aka adjoint representation of SU(2) flavour symmetry, because the up and down quarks belong doublet rep of SU(2) and a pion is a quark and anti-quark, and su(2) cross su(2)-bar is the adjoint rep.
  7. The SU(2) flavour symmetry allows fun games with chiral symmetry and in particular, since su(2) also describes spatial rottations, one can play games with non-trivial topological mappings of the embedding of pion fields into 3D space. i.e. mappings because of the non-trivial fundamental group.
  8. Skyrme's topological soliton aka skyrmion aka 'cloud of pions' aka 'chiral model' is a decent one-parameter model of the nucleon (proton/neutron), which predicts a variety of nuclear properties fairly accurately with only one free parameter.

linas 01:00, 24 May 2005 (UTC)

Do pions mediate the strong force? gluons do this job! Lluis M. 12:00, 24-12-2005
No and Yes. Pions mediate what is now called the inter-nucleon force, but used to be called the strong force before quarks were discovered. linas 15:55, 23 December 2005 (UTC)

It should be said somewhere that pions are the (pseudo-)Goldstone bosons associated to the chiral SU(2) spontaneus symmetry breaking of QCD.

SU(2) \otimes \overline{SU(2)} \approx SO(3) \oplus U(1)

doesn't look right. I'm not even sure what \overline{SU(2)} means, but if we ignore the overline, the LHS isn't the same as the RHS. Not that I know what \approx means in this context.

Agreed. It didn't make any sense (what on earth is the direct sum of two lie groups?). I've removed it. It doesn't detract from
the section. Below is exactly what I removed.
Thus, one has
SU(2) \otimes \overline{SU(2)} \approx SO(3) \oplus U(1)
which is one of the many relationships which lends weight to the quark model of pions and nucleons.
Shambolic Entity 04:30, 9 November 2006 (UTC)

errm...the feynman diagram for the pion decay is not correct: the W boson is represented by a dashed line, not a wavy one (which represents the photon). unfortunately atm. i do neither have time nor the experience to create a new one. anyone?! cheers. Diekuhmachtmuh 11:48, 17 November 2006 (UTC)

ok, edit: i just recognized that in respect to the electroweak unification, W- and Z-bosons are represented by the same symbolic propagator as the photon, that is, a wavy line. however, im almost all books and sources the like that i came across, W and Z are still represented by dashed lines. so much about consistency and convention, argl ;-). cheers. Diekuhmachtmuh 12:03, 17 November 2006 (UTC)

pions are not leptons, right? (see "History")

Pions are Bosons. Also, the Pi-Zero quark make-up below the image is wrong. Should be: \mathrm{\frac{u\bar{u} - d \bar{d}}{\sqrt{2}}}. I'll change it later today. Arthur (Lazyrussian) (talk) 13:01, 3 June 2008 (UTC)