  In this paper, we discuss limits on various astro-particle scenarios if the
scale \textit{and} the reheat temperature of the last relevant inflation were
very high. While the observed "B" like pattern of polarizations of the CMB
suggest a very high ($\ge 10^{16}\ GeV$) scale of a primordial (which motivated
this work initially) and may reflect effects of dust, we believe that
addressing these issues is nonetheless very useful. We recall the potential
difficulties with various topological defects - monopoles, strings and domain
walls generated at the SSB (spontaneous symmetry breaking) of various gauge
symmetries. The main part of the paper is devoted to discussing difficulties
with long-lived heavy particles, which could be dark matter but cannot
efficiently annihilate to the required residual density because of basic
S-Matrix unitarity/analyticity limits. We indicate in simple terms yet in some
detail how the WIMP miracle occurs at $M(X)\sim{TeV}$ and how the axiomatic
upper bound presently updated to $M(X) \le{110 TeV}$ was originally derived by
Greist and Kamionokowski. We also argue that generically we expect the stronger
$M(X)\le{20\ GeV}$ bound to hold. We then elaborate on the pure particle
physics approaches aiming to enhance the annihilation and evade the bounds. We
find that the only and in fact very satisfactory way of doing this requires
endowing the particles with gauge interactions with a confinement scale lower
than $M(X)$. We also comment on models with light $O(KeV)$ dark matter, which
was supposed to be frozen in via out-of equilibrium processes so as to have the
right relic densities pointing out that in many such cases \textit{very} low
reheat temperatures are indeed required and speculate on the large desert
scenario of particle physics. Most of what we discuss is not new but was not
presented in a coherent fashion.
