Small Instantons and Weak Scale String Theory

TL;DR

This paper explores how shrinking instantons in heterotic string compactifications can lead to very low string scales and weakly coupled gauge groups, potentially impacting supersymmetry breaking mechanisms.

Contribution

It demonstrates that small instantons can generate new gauge symmetries and allow for arbitrarily low heterotic string scales, offering novel insights into string phenomenology.

Findings

Weakly or strongly coupled heterotic string scales can be arbitrarily low.

SO(32) and E8×E8 gauge groups can become very weakly coupled.

Small instantons may play a role in supersymmetry breaking.

Abstract

We consider heterotic string compactifications to four dimensions when instantons shrink to zero size. If the standard model gauge group originates from the new gauge symmetry associated with the small instantons singularity, then the weakly or strongly coupled heterotic string scales can be taken to be arbitrarily low. The SO(32) and E_8\times E_8 gauge groups can then be very weakly coupled even at the string scale and behave as non-abelian global symmetries. We comment on a possible role of small instantons in supersymmetry breaking.