We consider a model with a toroidally compactified extra dimension giving
rise to a temperature-dependent 4d effective potential with one-loop
contributions due to the Casimir effect, along with a 5d cosmological constant.
The forms of the effective potential at low and high temperatures indicates a
possibility for the formation of a domain wall bubble, formed by the modulus
scalar field, surrounding an evaporating black hole. This is viewed as an
example of a recently proposed black hole vacuum bubble arising from
matter-sourced moduli fields in the vicinity of an evaporating black hole [D.
Green, E. Silverstein, and D. Starr, Phys. Rev. D74, 024004 (2006),
arXiv:hep-th/0605047]. The black hole bubble can be highly opaque to lower
energy particles and photons, and thereby entrap them within. For high
temperature black holes, there may also be a symmetry-breaking black hole
bubble of false vacuum of the type previously conjectured by Moss [I.G. Moss,
Phys. Rev. D32,1333 (1985)], tending to reflect low energy particles from its
wall. A double bubble composed of these two different types of bubble may form
around the black hole, altering the hole's emission spectrum that reaches
outside observers. Smaller mass black holes that have already evaporated away
could have left vacuum bubbles behind that contribute to the dark matter.Comment: 20 pages; to appear in Phys.Rev.