| DATE: |
2006-11-17 16:00 - 17:00 |
| PLACE: |
Kenkyu Honkan Rm. 321 |
| TITLE: |
A Skyrme-type description of baryons derived from low dimensional NJL models |
| CONTACT: |
tsuda |
| SPEAKER: |
Konrad Urlichs (Erlangen University) |
| LANGUAGE: |
English |
| ABSTRACT: |
The NJL model in 1+1 dimensions is a quantum field theory of fermions with a four-fermion interaction term. The Lagrangian shows a continuous chiral symmetry, spontaneously broken by the vacuum. In the large N limit this model can be described analytically, using mean field methods. Baryons emerge as topologically non-trivial pion field configurations. The baryon number is equal to the winding number, counting how many times the mean field winds around the circle of degenerate vacuum states. This picture is reminiscent of the Skyrme model used in nuclear physics. This result can be extended to the massive model, where shape and mass of the baryon (=Skyrmion) are given in a systematic expansion in powers of the pion mass. Because the mean field varies slowly in space for small pion masses, the derivative expansion is the relevant theoretical tool. We also formulate a 2+1 dimensional version of the NJL model, which again leads to a Skyrme type description of baryons. In contrast to 1+1 dimensions, the baryon is not massless, but a state with vanishing binding energy.
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