Pion and sigma meson properties in a relativistic quark model

A variety of strong and electroweak interaction properties of a pion and a light scalar sigma meson are computed in a relativistic quark model. Under the assumption that the resulting coupling of these mesons to the constituent quarks is identical, the sigma meson mass is determined as M-sigma=385.4 MeV. We discuss in detail the gauging of the nonlocal meson-quark interaction and calculate the electromagnetic form factor of the pion and the form factors of the pi(0)-->gammagamma and sigma-->gammagamma processes. We obtain explicit expressions for the relevant form factors and evaluate the leading and next-to-leading orders for large Euclidean photon virtualities. Turning to the decay properties of sigma, we determine the width of the electromagnetic sigma-->gammagamma transition and discuss the strong decay sigma-->pipi. In a final step we compute the nonleptonic decays D-->sigmapi and B-->sigmapi relevant for the possible observation of the sigma meson. All our results are compared to available experimental data and to results of other theoretical studies.