Microscopic primordial black holes and extra dimensions

We examine the production and evolution of microscopic black holes in the early universe in the large extra dimensions scenario. We demonstrate that, unlike in the standard four-dimensional cosmology, in large extra dimensions absorption of matter from the primordial plasma by the black holes is significant and can lead to rapid growth of the black hole mass density. This effect can be used to constrain the conditions present in the very early universe. We demonstrate that this constraint is applicable in regions of parameter space not excluded by existing bounds.

Figure 1

$M_{\mathrm{thresh}}$ (see text) as a function of temperature, for a thermalized (solid) and empty (dashed) bulk. Here, $M_{*}=1\mathrm{TeV}$ and from bottom to top, $n=2$, 3, 4, 5, 6, 7.

Figure 2

The maximum mass $M_{\max }$ attained by a black hole in the empty bulk scenario shown as a function of time after the big bang. From top to bottom, $n=3$, 4, 5, 6, 7.

Figure 3

The solid lines show the evolution of the mass of a black hole with $M_0=10M_{\mathrm{thresh}}$ for $M_{*}=1\mathrm{TeV}$ and $n=3$, assuming an empty bulk. From top to bottom, $T_0=1000$, 900, 400, 50 GeV. The dashed line is $M_{\max }$.

Figure 4

(a) Differential production rate of microscopic black holes in the early universe for $n=3$. From top to bottom, $T=700$, 500, 400, 300, 200 GeV. (b) Total production rate. From left to right, $n=3$, 4, 5, 6, 7.

Figure 5

Bounds on $T_I$ and $M_{*}$ from BBN and overclosure of the universe for an empty bulk. The dashed lines represent $T=M_{*}$ above which the semiclassical description fails. The regions above the solid lines are ruled out. (a) For an empty bulk, from bottom to top, $n=3$, 4, 5. (b) For a thermalized bulk, from bottom to top $n=3$, 4, 5, 6, 7. The inset is a magnification of the $n=3$ curve showing the kink arising from a switch from the overclosure bound to the BBN bound.

Figure 6

Diffuse gamma ray bounds from KK graviton decay. From left to right, $n=7$, 6, 5, 4, 3. The region to the left of the curves is excluded.