Scalar Mesons in Radiative Decays and pi-pi Scattering

In this write-up, I summarize the analyses on the low-lying scalar mesons I have done recently with my collaborators. I first briefly review the previous analyses on the hadronic processes related to the scalar mesons, which shows that the scalar nonet takes dominantly the $qq\bar{q}\bar{q}$ structure. Next, I summarize our analysis on the radiative decays involving the scalar mesons, which indicates that it is difficult to distinguish $qq\bar{q}\bar{q}$ picture and $q\bar{q}$ picture just from radiative decays. Finally, I summarize our recent analysis on the $\pi$-$\pi$ scattering in the large $N_c$ QCD, which indicates that the $\sigma$ meson is likely the $qq\bar{q}\bar{q}$ state.