  A pseudoscalar or scalar particle $\phi$ that couples to two photons but not
to leptons, quarks and nucleons would have effects in most of the experiments
searching for axions, since these are based on the $a \gamma \gamma $ coupling.
We examine the laboratory, astrophysical and cosmological constraints on $\phi$
and study whether it may constitute a substantial part of the dark matter. We
also generalize the $\phi$ interactions to possess $SU(2) \times U(1)$ gauge
invariance, and analyze the phenomenological implications.
