Seeking the Ground State of String Theory

TL;DR

This paper discusses the challenges in identifying the ground state of string theory, explores various stabilization ideas, and considers the implications of a potentially low string scale and enhanced symmetries.

Contribution

It reviews the difficulties in understanding the string ground state and evaluates stabilization schemes like Kahler stabilization and Maximally Enhanced Symmetry.

Findings

Systematic approximation methods are unlikely to fully determine the ground state.

Gauge coupling properties suggest possible systematic insights.

Maximally Enhanced Symmetry is a natural and potentially predictive hypothesis.

Abstract

Recently, a number of authors have challenged the conventional assumption that the string scale, Planck mass, and unification scale are roughly comparable. It has been suggested that the string scale could be as low as a TeV. The greatest obstacle to developing a string phenomenology is our lack of understanding of the ground state. We explain why the dynamics which determines this state is not likely to be accessible to any systematic approximation. We note that the racetrack scheme, often cited as a counterexample, suffers from similar difficulties. We stress that the weakness of the gauge couplings, the gauge hierarchy, and coupling unification suggest that it may be possible to extract some information in a systematic approximation. We review the ideas of Kahler stabilization, an attempt to reconcile these facts. We consider whether the system is likely to sit at extremes of the moduli space, as in recent proposals for a low string scale. Finally we discuss the idea of Maximally Enhanced Symmetry, a hypothesis which is technically natural, compatible with basic facts about cosmology, and potentially predictive.