  Dark matter (DM) annihilation could in principle contribute to the diffuse
cosmic gamma-ray back- ground (CGB). While with standard assumptions for
cosmological and particle physics parameters this contribution is expected to
be rather small, a number of processes could boost it, including a
larger-than-expected DM annihilation cross-section, or the occurance of DM
substructures such as DM mini-spikes around intermediate-mass black holes. We
show that angular correlations of the CGB provide a tool to disentangle the
signal induced by DM annihilation in mini-spikes from a conventional
astrophysical component. Treating blazars as a known background, we study the
prospects for detecting DM annihilations with the Fermi Gamma-Ray Space
Telescope for different choices of DM mass and annihilation channels.
