Constraints on Primordial Black Holes From Big Bang Nucleosynthesis
  Revisited
  As space expands, the energy density in black holes increases relative to
that of radiation, providing us with motivation to consider scenarios in which
the early universe contained a significant abundance of such objects. In this
study, we revisit the constraints on primordial black holes derived from
measurements of the light element abundances. Black holes and their Hawking
evaporation products can impact the era of Big Bang Nucleosynthesis (BBN) by
altering the rate of expansion at the time of neutron-proton freeze-out, as
well as by radiating mesons which can convert protons into neutrons and vice
versa. Such black holes can thus enhance the primordial neutron-to-proton
ratio, and increase the amount of helium that is ultimately produced.
Additionally, the products of Hawking evaporation can break up helium nuclei,
which both reduces the helium abundance and increases the abundance of
primordial deuterium. Building upon previous work, we make use of modern
deuterium and helium measurements to derive stringent constraints on black
holes which evaporate in $t_{\rm evap} \sim 10^{-1}$ s to $\sim 10^{13}$ s
(corresponding to $M \sim 6\times 10^8$ g to $\sim 2 \times 10^{13}$ g,
assuming Standard Model particle content). We also consider how physics beyond
the Standard Model could impact these constraints. Due to the gravitational
nature of Hawking evaporation, the rate at which a black hole evaporates, and
the types of particles that are produced through this process, depend on the
complete particle spectrum. Within this context, we discuss scenarios which
feature a large number of decoupled degrees-of-freedom (\ie~large hidden
sectors), as well as models of TeV-scale supersymmetry.
