Infrared Hierarchy, Thermal Brane Inflation and Superstrings as Superheavy Dark Matter

TL;DR

The paper investigates a brane-world scenario with TeV-scale quantum gravity and large extra dimensions, aiming to avoid the standard high-reheating-temperature problems. It introduces a thermal stabilization mechanism in which repelling branes are glued by temperature, producing a brief thermal brane inflation with $n_e = \ln(T_{in}/T_c)$ e-foldings and a low reheating temperature $T_R$, followed by brane separation and the stretching of sub-millimeter strings that can act as superheavy dark matter. It further explores an infrared (inverted-hierarchy) mechanism that can stabilize brane separation at large distances, linking the size of extra dimensions to IR dynamics. The work analyzes the role of bulk gravitons and bulk vacuum-energy effects, arguing that under reasonable assumptions the scenario can yield a consistent cosmology with a viable dark-matter candidate and without overproducing bulk relics.

Abstract

In theories with TeV scale quantum gravity the standard model particles live on a brane propagating in large extra dimensions. Branes may be stabilized at large (sub-millimeter) distances from each other, either due to weak Van der Waals type interactions, or due to an infrared analog of Witten's inverse hierarchy scenario. In particular, this infrared stabilization may be responsible for a large size of extra dimensions. In either case, thermal effects can drive a brief period of the late inflation necessary to avoid the problems with high reheating temperature and the stable unwanted relics. The main reason is that the branes which repel each other at zero temperature can be temporarily glued together by thermal effects. It is crucial that the temperature needed to stabilize branes on top of each other can be much smaller than the potential energy of the bound-state, which drives inflation. After 10-15 $e$-foldings bound-states cool below the critical temperature and decay ending inflation. The parallel brane worlds get separated at this stage and superstrings (of a sub-millimeter size) get stretched between them. These strings can have the right density in order to serve as a superheavy dark matter.