Heating in Brane Inflation and Hidden Dark Matter

TL;DR

This work analyzes how energy from brane-antibrane annihilation at the end of brane inflation in warped, multi-throat compactifications is transferred to Standard Model degrees of freedom. By modeling KK modes, tunneling between throats, and the ensuing thermodynamic history, it shows that warped geometries suppress gravitons and KK relics, enabling reheating compatible with BBN even in complex multi-throat layouts. It identifies three new dark matter candidates—warped KK modes in the SM throat, hidden DM from KK modes tunneled to other throats, and high-angular-momentum KK remnants—each with distinct production and interaction properties, and it highlights a dynamical mechanism that preferentially heats long throats. The results imply rich phenomenology for hidden sectors, cosmic rays, and gravitational signatures, offering novel avenues to test string-inspired cosmologies through dark matter and high-energy astrophysical observations.

Abstract

Towards the end of brane inflation, the brane pair annihilation produces massive closed strings. The transfer of this energy to Standard Model (SM) open string modes depends on where the SM branes and the brane annihilation are located: in the bulk, in the same throat or in different throats. We find that, in all cases as long as the brane annihilation and the SM branes are not both in the bulk, the transfer of energy to start the hot big bang epoch can be efficient enough to be compatible with big bang nucleosynthesis. The suppression of the abundance of the graviton and its Kaluza-Klein (KK) thermal relics follows from the warped geometry in flux compactification. This works out even in the scenarios where a long period of tunneling is expected. In the multi-throat scenario, we find a dynamical mechnism of selecting a long throat as the SM throat. We establish three new dark matter candidates: KK modes with specific angular momentum in the SM throat, those in the brane annihilation throat, and different matters generated by KK modes tunneled to other throats. Since the latter two couple to the visible matter sector only through graviton mediation, they behave as hidden dark matter. Hidden dark matter has novel implications on the dark matter coincidence problem and the high energy cosmic rays.