The cosmological constant in the brane world of string theory on $S^{1}/Z_{2}$

TL;DR

This paper explores how string theory brane worlds with extra dimensions can naturally reduce the cosmological constant to observed levels and provides stable radion configurations, offering a potential solution to the cosmological constant problem.

Contribution

It derives explicit field equations for orbifold branes in string theory and demonstrates a mechanism to lower the cosmological constant using large extra dimensions, with stability analysis included.

Findings

Effective cosmological constant can be lowered to observed value

Radion stability is confirmed via Goldberger-Wise mechanism

Generalized Friedmann equations are derived for brane cosmology

Abstract

Orbifold branes in string theory are investigated, and the general field equations on the branes are given explicitly for type II and heterotic string. It is shown that the effective cosmological constant on each of the two branes can be easily lowered to its current observational value, using large extra dimensions. This is also true for type I string. The radion stability is studied by using the Goldberger-Wise mechanism, and shown explicitly that it is stable. Therefore, brane world of string theory provides a viable and built-in mechanism for solving the long-standing cosmological constant problem. Applying the formulas to cosmology, we obtain the generalized Friedmann equations on each of the two branes.