Large radii and string unification

TL;DR

This paper investigates how large internal dimensions in heterotic string models influence strong coupling effects and gauge unification, linking thresholds to dual theories like type I superstring and M-theory.

Contribution

It demonstrates that large internal dimensions lead to thresholds near the unification scale, providing a scenario for unifying gravity and gauge interactions in string theory.

Findings

Thresholds appear near 10^16 GeV for one large dimension.

Inverse M-theory dimension size correlates with four-fermion operator activation energy.

Large dimensions affect strong coupling effects and unification scales.

Abstract

We study strong coupling effects in four-dimensional heterotic string models where supersymmetry is spontaneously broken with large internal dimensions, consistently with perturbative unification of gauge couplings. These effects give rise to thresholds associated to the dual theories: type I superstring or M-theory. In the case of one large dimension, we find that these thresholds appear close to the field-theoretical unification scale $\sim 10^{16}$ GeV, offering an appealing scenario for unification of gravitational and gauge interactions. We also identify the inverse size of the eleventh dimension of M-theory with the energy at which four-fermion effective operators become important.