Phenomenology, astrophysics, and cosmology of theories with submillimeter dimensions and TeV scale quantum gravity

Abstract

We recently proposed a solution to the hierarchy problem not relying on low-energy supersymmetry or technicolor. Instead, the problem is nullified by bringing quantum gravity down to the TeV scale. This is accomplished by the presence of n ≥ 2 new dimensions of sub-millimeter size, with the SM fields localised on a 3-brane in the higher dimensional space. In this paper we systematically study the experimental viability of this scenario. Constraints arise both from strong quantum gravitational effects at the TeV scale, and more importantly from the production of massless higher dimensional gravitons with TeV suppressed couplings. Theories with n > 2 are safe due mainly to the infrared softness of higher dimensional gravity. For n = 2, the six dimensional Planck scale must be pushed above ∼ 30 TeV to avoid cooling SN1987A and distortions of the diffuse photon background. Nevertheless, the particular implementation of our framework within type I string theory can evade all constraints, for any n ≥ 2, with string scale m s ∼ 1 TeV. We also explore novel phenomena resulting from the existence of new states propagating in the higher dimensional space. The Peccei-Quinn solution to the strong CP problem is revived with a weak scale axion in the bulk. Gauge fields in the bulk can mediate repulsive forces ∼ 10 6 − 10 8 times stronger than gravity at sub-mm distances, as well as help stabilize the proton. Higher-dimensional gravitons produced on our brane and captured on a different "fat" brane can provide a natural dark matter candidate.

New developments in the Casimir effect

“…This means that the Casimir effect becomes a new non-accelerator test for the search of hypothetical forces and associated light and massless elementary particles. Tests of this type take on great significance in the light of the exciting new ideas that the gravitational and gauge interactions may become unified at the weak scale (see, e.g., [290]). As a consequence, there should exist extra spatial dimensions compactified at a relatively large scale of 10 −3 m or less.…”

Estimate for the size of the compactification radius of a one extra dimension universe

“…and refer the reader to the bibliography [9] for more details. Now, comparing (1) and (4), we find the following constraint relation…”

The Casimir effect in the presence of compactified universal extra dimensions

“…However, recently models with compactification radii up to the mm-scale and with a lowered Planck-Mass (TeV region) have been introduced [5,6,7,8,9,10,11,12]. In the ADD [7] and RS [10] type of models, the hierarchyproblem is solved or reformulated, resp.…”