Abstract
We present estimates for the rates of the processes χχ→γγ and χχ→Vγ, where χ is a heavy-neutral-fermion candidate for galactic cold dark matter and V is a vector quarkonium state J/ψ(3097) or Υ(9460). A discrepancy with a previous estimate of the rate of the photino pair annihilation process γ̃γ̃→γγ is uncovered and its origin discussed. We explore the possibility that some of the processes considered may be astrophysically significant sources of monochromatic γ-ray lines, in the energy range of a few to a few tens of GeV, for which theoretical estimates of the background γ-ray flux are unfortunately subject to large uncertainties.

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