Dangerous Angular KK/Glueball Relics in String Theory Cosmology

TL;DR

This paper investigates the potential cosmological dangers posed by long-lived Kaluza-Klein particles and glueballs in string theory models with warped throats, analyzing their interactions, decay channels, and observational constraints.

Contribution

It provides a detailed study of the interactions and decay mechanisms of angular KK modes and glueballs, and derives cosmological constraints on warped compactification parameters.

Findings

Angular KK modes can be long-lived and pose cosmological risks.

Observational constraints exclude significant regions of warped geometry parameter space.

Couplings of angular KK particles can be weaker than gravity.

Abstract

The presence of Kaluza-Klein particles in the universe is a potential manifestation of string theory cosmology. In general, they can be present in the high temperature bath of the early universe. In particular examples, string theory inflation often ends with brane-antibrane annihilation followed by the energy cascading through massive closed string loops to KK modes which then decay into lighter standard model particles. However, massive KK modes in the early universe may become dangerous cosmological relics if the inner manifold contains warped throat(s) with approximate isometries. In the complimentary picture, in the AdS/CFT dual gauge theory with extra symmetries, massive glueballs of various spins become the dangerous cosmological relics. The decay of these angular KK modes/glueballs, located around the tip of the throat, is caused by isometry breaking which results from gluing the throat to the compact CY manifold. We address the problem of these angular KK particles/glueballs, studying their interactions and decay channels, from the theory side, and the resulting cosmological constraints on the warped compactification parameters, from the phenomenology side. The abundance and decay time of the long-lived non-relativistic angular KK modes depend strongly on the parameters of the warped geometry, so that observational constraints rule out a significant fraction of the parameter space. In particular, the coupling of the angular KK particles can be weaker than gravitational.