On Fluxed Instantons and Moduli Stabilisation in IIB Orientifolds and F-theory

TL;DR

This work tackles moduli stabilization in Type IIB orientifolds with chiral matter by studying E3-instantons carrying world-volume flux. It shows that instanton flux can cancel charged zero modes from D7-brane intersections, rendering nonperturbative contributions gauge-invariant and capable of fixing the Kähler moduli and NS-axions, even in the presence of chirality. By combining macroscopic gauging with a microscopic zero-mode analysis, the authors demonstrate a theta-function structure from flux sums and the possibility to stabilize all $T_\alpha$ and $G^a$ within the geometric regime, potentially via a single ample instanton. The discussion extends to F-theory, where Higgsing of abelian U(1)s through exceptional gauge sector dynamics provides an additional mechanism to realize moduli stabilization in chirally engineered vacua, highlighting a robust path for realistic compactifications.

Abstract

We study the superpotential induced by Euclidean D3-brane instantons carrying instanton flux, with special emphasis on its significance for the stabilisation of Kahler moduli and Neveu-Schwarz axions in Type IIB orientifolds. Quite generally, once a chiral observable sector is included in the compactification, arising on intersecting D7-branes with world-volume flux, resulting charged instanton zero modes prevent a class of instantons from participating in moduli stabilisation. We show that instanton flux on Euclidean D3-branes can remove these extra zero modes and helps in reinstating full moduli stabilisation within a geometric regime. We comment also on the F-theoretic description of this effect of alleviating the general tension between moduli stabilisation and chirality. In addition we propose an alternative solution to this problem based on dressing the instantons with charged matter fields which is unique to F-theory and cannot be realised in the weak coupling limit.