de Sitter Thin Brane Model

TL;DR

This paper explores a de Sitter thin brane model to address the large mass hierarchy problem in an expanding universe, finding that a negative 5D cosmological constant naturally explains the hierarchy and yields KK modes around 100 GeV.

Contribution

It introduces a de Sitter thin brane model with negative 5D cosmological constant, providing a natural explanation for the large hierarchy and analyzing KK mode spectra.

Findings

Negative $ m \Lambda_5$ naturally explains the hierarchy.

KK modes have masses around 100 GeV, independent of Hubble parameter.

Large hierarchy between Hubble scale and Planck scale is achieved.

Abstract

We discuss the large mass hierarchy problem in a braneworld model which represents our acceleratively expanding universe. The Randall-Sundrum (RS) model with warped one extra dimension added to flat 4-dimensional space-time cannot describe our expanding universe. Here, we study instead the de Sitter thin brane model. This is described by the same action as that for the RS model, but the 4-dimensional space-time on the branes is $\rm dS_4$. We study the model for both the cases of positive 5-dimensional cosmological constant $\Lambda_5$ and negative one. In the positive $\Lambda_5$ case, the 4-dimensional large hierarchy necessitates a 5-dimensional large hierarchy, and we cannot get a natural explanation. On the other hand, in the negative $\Lambda_5$ case, the large hierarchy is naturally realized in the 5-dimensional theory in the same manner as in the RS model. Moreover, another large hierarchy between the Hubble parameter and the Planck scale is realized by the ${\mathcal O}(10^2)$ hierarchy of the 5-dimensional quantities. Finally, we find that the lightest mass of the massive Kaluza-Klein modes and the intervals of the mass spectrum are of order $10^2\,\rm GeV$, which are the same as in the RS case and do not depend on the value of the Hubble parameter.