Analytic Description of Primordial Black Hole Formation from Scalar
  Field Fragmentation
  Primordial black hole (PBH) formation is a more generic phenomenon than was
once thought. The dynamics of a scalar field in inflationary universe can
produce PBHs under mild assumptions regarding the scalar potential. In the
early universe, light scalar fields develop large expectation values during
inflation and subsequently relax to the minimum of the effective potential at a
later time. During the relaxation process, an initially homogeneous scalar
condensate can fragment into lumps via an instability similar to the
gravitational (Jeans) instability, where the scalar self-interactions, rather
than gravity, play the leading role. The fragmentation of the scalar field into
lumps (e.g. Q-balls or oscillons) creates matter composed of relatively few
heavy "particles", whose distribution is subject to significant fluctuations
unconstrained by comic microwave background (CMB) observations and unrelated to
the large-scale structure. If this matter component comes to temporarily
dominate the energy density before the scalar lumps decay, PBHs can be
efficiently produced during the temporary matter-dominated era. We develop a
general analytic framework for description of PBH formation in this class of
models. We highlight the differences between the scalar fragmentation scenario
and other commonly considered PBH formation models. Given the existence of the
Higgs field and the preponderance of scalar fields within supersymmetric and
other models of new physics, PBHs constitute an appealing and plausible
candidate for dark matter.
