We nonperturbatively investigate a fermion spectrum at finite temperature in a chiral invariant linear sigma model. Coupled Schwinger-Dyson equations for fermion and boson are developed in the real time formalism and solved numerically. From the coup
ling of a massless fermion with a massive boson, the fermion spectrum shows a three-peak structure at some temperatures even for the strong coupling region. This means that the three-peak structure which was originally found in the one-loop calculation is stable against higher order corrections even in the strong coupling region.
In this write-up we summarize the main result of our analysis on the thermal dilepton production rate from the dropping rho based on the vector manifestation (VM). In the analysis, we showed that the effect of the strong violation of the vector domin
ance (VD) predicted by the VM, substantially suppresses the dilepton production rate compared with the one predicted by assuming the VD together with the dropping rho.
In this write-up, we summarize our recent analysis of radiative decays involving light scalar mesons. Our analysis using the vector meson dominance model at tree level indicates that it may be difficult to distinguish $qqbar{q}bar{q}$ picture and $qb
ar{q}$ picture for the light scalar nonet. Our result on the process of $phi to pi^0 eta gamma$ shows that the derivative-type $f_0 Kbar{K}$ interaction reproduces experimental data below 950 GeV well, but gives a poor fit above 950 GeV, i.e., in the energy region around the mass of $a_0(980)$, but that the discrepancy can be compensated by the effect of the $K$ loop.
