The Cosmological Constant Problem and the Extra Dimensions of $\mathcal{N}=2$ $\mathcal{D}=5$ Supergravity

Abstract

We propose an interpretation for the cosmological constant problem based on modeling the universe as a 3-brane embedded in the bulk of 5-dimensional supergravity with hypermultiplets. When solving the modified Friedmann equations the complex structure moduli of the Calabi-Yau manifold cancel the large value of the vacuum energy density on the brane, wherein this value transfers to an Anti-de Sitter fifth dimensional bulk compactified on a scale $ (\sim 10^{-26} ~\text{m}) $. An effective dark energy density is produced on the brane which equals the observed value responsible for the late-time acceleration of the universe. The bulk undergoes a decelerated contraction while we show that cosmic expansion of the brane-universe consists with the recent observed data of the $\Lambda$CDM model. On the other hand, through this model, the hierarchy between the electroweak scale $(M_{EW}= 100 ~ \text{GeV})$ and the Planck scale $(M_{pl} \sim 10^{18} ~ \text{GeV})$ is interpreted by compactifying the 6-extra dimensions of $\mathcal{D}=5$ supergravity on a sub-millimeters scale, where the fundamental scale of gravity within these extra dimensions is $\mathcal{M}_{EW}$.