An alternative to anti-branes and O-planes?

TL;DR

This work shows that de Sitter vacua can arise in type IIA flux compactifications on an isotropic $\mathbb{Z}_{2}\times \mathbb{Z}_{2}$ orbifold using D6-branes without O-planes or anti-branes by combining perturbative flux-induced superpotentials with a non-perturbative sector from gaugino condensation. A two-term non-perturbative superpotential $W_{\mathrm{(non-pert.)}}=(Z_{1}+iZ_{2})e^{i\alpha S}+(Z_{3}+iZ_{4})e^{i\beta T}$ stabilizes directions that remain runaway under the perturbative potential, though generic uplift schemes induce tachyons due to large off-diagonal mass mixing. A systematic search around the origin of moduli space yields two fully stable dS critical points with positive non-isotropic spectra and positive tadpoles $N_{6}^{||}$ and $N_{6}^{\perp}$, showing that dS without anti-branes or O-planes is possible in this framework albeit with important non-perturbative corrections. The paper discusses scale separation prospects, finding that Planck, string, and KK scales can be hierarchically separated in a controlled limit, while a clean separation of the Hubble scale remains delicate and may require fine-tuning. Overall, the results advance the exploration of metastable dS vacua in string theory beyond the standard KKLT ingredients, while highlighting important open questions about prefactor dependence on moduli and full ten-dimensional consistency.

Abstract

In this paper we consider type IIA compactifications in the isotropic Z2 x Z2 orbifold with a flux-induced perturbative superpotential combined with non-perturbative effects. Without requiring the presence of O-planes, and simply having D6-branes as local sources, we demonstrate the existence of de Sitter (dS) critical points, where the non-perturbative contributions to the cosmological constant have negligible size. We note, however, that these solutions generically have tachyons. By means of a more systematic search, we are able to find two examples of stable dS vacua with no need for anti-branes or O-planes, which, however, exhibit important non-perturbative corrections. The examples that we present turn out to remain stable even after opening up the fourteen non-isotropic moduli.