Finite temperature spectral functions of the linear O(N)-model at large-N applied to the π–σ system

Abstract The thermal evolution of the spectral densities derivable from the two-point functions of the elementary and the quadratic composite fields of the O ( N ) model is studied in the isosinglet channel and in the broken symmetry phase at infinite N . The results are applied with realistic parameter values to the N =4 case. They provide a reasonable description of the σ meson at T =0. Threshold enhancement is observed around T∼1.07 m π . For higher temperatures the maximum of the spectral function in the single meson channel decreases and becomes increasingly rounded.