The refractive properties of the gluon plasma in SU(2) gauge theory

Abstract

The deconfined phase in finite temperature SU(2) gauge theory shows clear interaction effects in the temperature range 1≦T/T _c≦2. The interaction measure Δ≡(ɛ−3P)/T ⁴, defined in terms of the energy density ɛ and the pressureP, peaks at some temperatureT above the critical temperatureT _c and is different from zero in the entire temperature interval mentioned. High statistics lattice calculations provide numerical results for the pressureP and the entropy densitys≡(ɛ+P)/T. We interpret these results in terms of an ideal gas of quasi-gluons propagating in a refractive medium. The refractive properties of the medium are parametrized in terms of a temperature-dependent effective massM(T) of the excitations, which is determined from the lattice data. It shows a quite non-trivial behaviour:M(T) decreases fromT=T _c untilT≃2T _c; beyond this point it starts increasing again, and at high temperatures it approaches the perturbative thermal massM(T)∼gT.