A new bound on the low reheating temperature with dark matter
  We investigate a new bound on the low reheating temperature in a scenario
where the Universe experiences early matter-domination before reheating after
which the standard big bang cosmology begins. In many models of dark matter
(DM), the small scale fluctuations of DM grow during the early
matter-domination era and seed the formation of the ultracompact minihalos
(UCMHs). Using the constraints on the number of UCMHs from gamma-ray
observations, we find a lower bound on the reheating temperature between ${\cal
O}(10)~{\rm MeV} - {\cal O}(100)~{\rm MeV}$ for WIMP dark matter depending on
the nature of DM. A similar bound could be obtained for non-WIMP dark matter by
observing UCMHs gravitationally such as pulsar timing, microlensing and so on
in some future observations.
