Coping With Strongly Coupled String Theory

TL;DR

This paper demonstrates that under certain assumptions, strongly coupled string theories can still yield reliable low-energy predictions, with supersymmetry and discrete gauge symmetries constraining the effective action.

Contribution

It shows that strong coupling effects can be controlled and understood through supersymmetry and discrete gauge symmetries, providing a framework for analyzing strongly coupled string theories.

Findings

Low energy spectrum remains consistent at strong and weak coupling.

Corrections to the superpotential and gauge coupling are small.

Large corrections to the Kahler potential occur, but do not alter low-energy predictions.

Abstract

String theory, if it describes nature, is probably strongly coupled. As a result, one might despair of making any statements about the theory. In the framework of a set of clearly spelled out assumptions, we show that this is not necessarily the case. Certain discrete gauge symmetries, combined with supersymmetry, tightly constrain the form of the effective action. Among our assumptions are that the true ground state can be obtained from some perturbative ground state by varying the coupling, and that the actual numerical value of the low energy field theoretic coupling ${g^2 \over 4\pi}$ is small. It follows that the low energy theory is approximately supersymmetric; corrections to the superpotential and gauge coupling function are small, while corrections to the Kahler potential are large; the spectrum of light particles is the same at strong as at weak coupling. We survey the phenomenological consequences of this viewpoint. We also note that the string axion can serve as QCD axion in this framework (modulo cosmological problems).