Cosmological Constraints on Bulk Neutrinos

TL;DR

Effects on cosmic microwave background anisotropies, big bang nucleosynthesis, deuterium and 6Li photoproduction, diffuse photon backgrounds, and structure formation are considered.

Abstract

Recent models invoking extra spacelike dimensions inhabited by (bulk) neutrinos are shown to have significant cosmological effects if the size of the largest extra dimension is R > 1 fm. We consider effects on cosmic microwave background anisotropies, big bang nucleosynthesis, deuterium and Li-6 photoproduction, diffuse photon backgrounds, and structure formation. The resulting constraints can be stronger than either bulk graviton overproduction constraints or laboratory constraints.

Figures (2)

• Figure 1: Cosmological constraints on Class I bulk neutrinos. Photoproduction and DEBRA constrain regions between the dot-dashed and short-dashed lines, respectively. The CMB constrains parameters below the labeled BOOMERanG, MAP, and Planck lines and above the long-dashed line. BBN constrains the region between the light solid lines. Parameters must lie above the heavy solid line to be consistent with the inferred age of the universe. The vertical lines arise from the neutrino oscillation and $^3$H endpoint limits on neutrino masses nuexptssolarpdgsuperk. Also shown is the $218 {\rm\,\mu m}$ Eöt-Wash limit on the size of two congruent large extra dimensions adelberger.
• Figure 2: Structure formation constraints on Class II bulk neutrino models with numbers of extra dimensions $n=6,5,4$ ($\Omega^{\rm HDM} > 0.1$ to the right of the slanted lines). By assumption, the size of the largest extra dimension is $R$, and all other dimensions have sizes $\ll {\rm pm}$. For example, the solar neutrino solutions of Dvali & Smirnov and Caldwell, Mohapatra, & Yellin models lie near $\odot$.