  Caustics are formally singular structures, with infinite density, that form
in collisionless media. The non-negligible velocity dispersion of dark matter
particles renders their density finite. We evaluate the maximum density of the
caustics within the framework of secondary infall model of formation of dark
matter haloes. The result is then used to demonstrate that caustics can be
probed by properly stacking the weak-lensing signal of about 600 haloes. CFHTLS
accompanied by X-ray observations and the space-based experiments like SNAP or
DUNE can provide us with the required statistics and hence a way of
distinguishing between the viable dark matter particle candidates. The
extension of our results to more realistic models including the effects of
mergers of haloes is briefly outlined.
