Cosmological Constraints on Theories with Large Extra Dimensions

TL;DR

This paper derives cosmological bounds on theories with large extra dimensions, showing that the fundamental scale must be significantly higher than 10 TeV, which constrains the size of extra dimensions beyond current experimental reach.

Contribution

It provides new lower bounds on the fundamental scale and size of extra dimensions using cosmological data, especially for the case of two extra dimensions.

Findings

Bound M_F > 110 TeV from gamma radiation constraints

Bound M_F > 6.5 h^(-1/2) TeV from graviton overclosure

Extra dimensions are constrained to be smaller than 10^-5 mm

Abstract

In theories with large extra dimensions, constraints from cosmology lead to non-trivial lower bounds on the fundamental scale M_F, corresponding to upper bounds on the radii of the compact extra dimensions. These constraints are especially relevant to the case of two extra dimensions, since only if M_F is 10 TeV or less do deviations from the standard gravitational force law become evident at distances accessible to planned sub-mm gravity experiments. By examining the graviton decay contribution to the cosmic diffuse gamma radiation, we derive, for the case of two extra dimensions, a conservative bound M_F > 110 TeV, corresponding to r_2 < 5.1 times 10^-5 mm, well beyond the reach of these experiments. We also consider the constraint coming from graviton overclosure of the universe and derive an independent bound M_F > 6.5 h^(-1/2) TeV, or r_2 < .015 h mm.