Chiral quark model with infrared cut-off for the description of meson properties in hot matter

Abstract

A simple chiral quark model of the Nambu--Jona-Lasinio (NJL) type with a quark confinement mechanism is constructed for the description of the light meson sector of QCD at finite temperature. Unphysical quark production thresholds in the NJL model are excluded by an infrared cut-off in the momentum integration within quark loop diagrams. This chiral quark model satisfies the low energy theorems. Using the vacuum masses and decay widths of π- and ρ-mesons for fixing the model parameters, the properties of the σ- meson are derived. Within the Matsubara formalism, the model is systematically extended to finite temperatures where chiral symmetry restoration due to a dropping constituent quark mass entails a vanishing of the infrared cut-off (deconfinement) at the pion Mott temperature T_c=186 MeV. Besides of the pion mass and weak decay constant, the masses, coupling constants and decay widths of σ- and ρ-mesons in hot matter are investigated. The quark-antiquark decay channel of the light mesons is opened for T>T_c only and becomes particularly strong for the ρ- meson. The two-pion decay channel below T_c has almost constant width for the ρ- meson up to T_c, but for the σ-meson it closes below T_c such that a scalar meson state with vanishing width is obtained as a precursor of the chiral/deconfinement transition.