Bose and Fermi Excitations in Hot and Dense QCD

por Oleg Kalashnikov (Lebedev Inst., Moscow)

jueves 18 feb. 1999 12:00 → 13:00 Europe/Madrid

Sala Seminarios (Dpto. de Fisica Teorica (UVEG))

The spectra of Bose and Fermi excitations are reviewed in hot and dense Abelian and non-Abelian theories for different gauges. Due to the medium all these spectra are multi-split and their branches have, as a rule, the finite energy gap at zero momentum (the effective thermal mass). The Bose (gluon or photon) spectra always have three branches (two transversal and one longitudinal) with the equal thermal masses proportional gT. The Fermi spectra have four or more branches which are very sensitive to the chosen gauge and the values of the m,\mu-parameters. Usually there are two one-particle (perturbative) branches and four collective ones: two branches represent the massive quasi-particle excitations with the usual properties and the other two - quasi-hole ones which occur only in the medium. The problem of gauge invariance which stays especially sharply for all Fermi spectra remains unsolved and we only demonstrate this difficulty comparing a number of the calculational results in the Feynman and Coulomb gauges.