  We report on a possible application of the HBT phenomenon in testing the
existence of two hypothetical phenomena. First, it is argued that the existence
of a rapidly developing parton cascade in the earliest stages of a high energy
nuclear collision process can be tested by studying two-photon HBT correlations
over a wide longitudinal momentum scale - corresponding to the early photon
emission time from the hypothetical parton system. This method provides the
needed selectivity for the early emitted photons, since the photons emitted at
later times correlate over progressively narrower momentum scales. Second, in a
similar way we argue that the existence of a hypothetic dark matter candidate,
the Weakly Interacting Massive Particle (WIMP), may be tested by studying HBT
correlations of cosmic gamma rays at a relatively long detection time scale -
corresponding to the very narrow spectral line of the photons emerging from
WIMP annihilations. Background photons leave no signature since they
essentially do not correlate.
