Effect of pion thermal width on the sigma spectrum

Abstract

We study the effect of the thermal width of $\pi$ on the spectral function of $\sigma$. In order to take into account a finite thermal width of $\pi$, we replace the internal pion mass in the self-energy of $\sigma$ with that of the complex pole found in a previous paper. The obtained spectral function for $T\aplg 100 {\rm MeV}$ turns out to possess two broad peaks. Although a sharp peak at $\sigma\to\pi\pi$ threshold was observed in the one-loop calculation without the pion thermal width, the peak is shown to be smeared out. We also search for the poles of the $\sigma$ propagator and analyze the behavior of the spectral function with these poles.