Electromagnetic trace anomaly in a generalized linear sigma model

摘要

We build the electromagnetic trace anomaly effective term for a generalized linear sigma model with twochiral nonets, one with a quark-antiquark structure and the other one with a four-quark content. In theleading order of this framework, we study the decays into two photons of the lowest isosinglet scalarmesons. We find that the direct inclusion of underlying mixing among two- and four-quark components inthe trace anomaly term is essential in order for the model prediction to agree with the available experimentaldata on the decay width of f_0(980) to two photons. Consequently, this sets a lower bound of 0.5 KeVon thedecay with of f_0(500) to two photons.