  We discuss the photoproduction of omega- and rho0-mesons off protons in the
particular channel where the target proton is excited to a Roper resonance
N*(1440). We propose a simple meson-exchange model for these processes in order
to evaluate their cross sections near threshold and at low momentum transfers.
It is suggested in particular that the differential cross section for the
associated photoproduction of a rho0-meson and a Roper resonance in these
kinematic conditions could provide direct information on the strength of the
scalar-isoscalar excitation of the N*(1440) and hence on the magnitude of an
effective sigma N N*(1440) coupling. The latter quantity is poorly known and of
much interest for the nuclear many-body problem.
