Supersymmetric Large Extra Dimensions and the Cosmological Constant: An Update

TL;DR

The article surveys supersymmetric large extra dimensions (SLED) as a potential resolution to the cosmological constant problem, positing two large extra dimensions where gravity propagates and brane tensions cancel bulk curvature at the classical level. It argues that bulk supersymmetry can keep quantum corrections small, yielding a residual vacuum energy $\delta\rho \sim m_{sb}^4$ with $m_{sb} \sim v$, consistent with observations in principle, while highlighting critical obstacles such as Weinberg's no-go, potential hidden tunings, the evolving radius problem, and the need for explicit bulk quantum calculations and radius stabilization. The work further discusses cosmological and observational implications, including possible quintessence-like behavior and distinctive collider/gravitational signatures, while acknowledging that a definitive proof requires detailed calculations of bulk quantum effects and stabilization mechanisms. Overall, SLED offers a promising but contingent framework that connects low-energy physics with extra-dimensional gravity, warranting further theoretical and experimental exploration.

Abstract

This article critically reviews the proposal for addressing the cosmological constant problem within the framework of supersymmetric large extra dimensions (SLED), as recently proposed in hep-th/0304256. After a brief restatement of the cosmological constant problem, a short summary of the proposed mechanism is given. The emphasis is on the perspective of the low-energy effective theory in order to see how it addresses the problem of why low-energy particles like the electron do not contribute too large a vacuum energy. This is followed by a discussion of the main objections, which are grouped into the following five topics: (1) Weinberg's No-Go Theorem. (2) Are hidden tunings of the theory required, and a problem? (3) Why should the mechanism not rule out earlier epochs of inflation? (4) How big are quantum effects, and which are the most dangerous? (5) Can the mechanism be consistent with cosmological constraints? It is argued that there are plausible reasons why the mechanism can thread the potential objections, but that a definitive proof that it does depends on addressing well-defined technical points. These points include identifying what fixes the size of the extra dimensions, checking how topological obstructions renormalize and performing specific calculations of quantum corrections. More detailed studies of these issues, which are well reach within our present understanding of extra-dimensional theories, are currently underway. As such, the jury remains out concerning the proposal, although the prospects for acquittal still seem good.