  We suggest a theoretical framework for the description of double photon and
proton-antiproton photoproduction off the proton gamma + p -> 2 gamma + p and
gamma + p -> antip + p + p which takes into account the contribution of the
scalar mesons f0(1370), f0(1500) and f0(1710). These scalars are considered as
mixed states of a glueball and nonstrange and strange quarkonia. Our framework
is based on the use of effective hadronic Lagrangians that phenomenologically
take into account two-gluon exchange effects governing the gamma + p -> 2 gamma
+ p and gamma + p -> antip + p + p processes. Present results can be used to
guide the possible search for these reactions by the GlueX Collaboration at
JLab.
