Dilepton and photon emission rates from a hadronic gas

We analyze the dilepton and photon emission rates from a hadronic gas using chiral reduction formulas and a virial expansion. The emission rates are reduced to pertinent vacuum correlation functions, most of which can be assessed from experiment. Our results indicate that in the low mass region, the dilepton and photon rates are enhanced compared to most of the calculations using chiral Lagrangians. The enhancement is further increased through a finite pion chemical potential. An estimate of the emission rates is also made using Haagʹs expansion for the electromagnetic current. The relevance of these results to dilepton and photon emission rates in heavy-ion collisions is discussed.