We study cosmological properties of type IIA compactifications on orientifolds of SU(3)-structure manifolds with non-vanishing geometric flux. These compactifications give rise to effective 4D N = 1 supergravity theories that do not fall under some recentlyproven no-go theorems against de Sitter vacua and slow-roll inflation. Focusing on a wellunderstood class of models based on coset spaces, however, we can use a refined no-go theorem that rules out de Sitter vacua and slow-roll inflation in all but one case. The refined no-go theorem uses the dilaton and a specific linear combination of the Kähler moduli, which is different from the overall volume modulus. It puts a lower bound on the first slow-roll parameter: ǫ ≥ 2. The only case not ruled out is the manifold SU(2)×SU(2), for which we indeed find critical points with ǫ numerically zero. However, all the points we could find have a tachyon corresponding to an eta-parameter η −2.4.
We consider string theory compactifications of the form AdS 4 ×M 6 with orientifold six-planes, where M 6 is a six-dimensional compact space that is either a nilmanifold or a coset. For all known solutions of this type we obtain the four-dimensional N = 1 low energy effective theory by computing the superpotential, the Kähler potential and the mass spectrum for the light moduli. For the nilmanifold examples we perform a cross-check on the result for the mass spectrum by calculating it alternatively from a direct Kaluza-Klein reduction and find perfect agreement. We show that in all but one of the coset models all moduli are stabilized at the classical level. As an application we show that all but one of the coset models can potentially be used to bypass a recent no-go theorem against inflation in type IIA theory.
We consider type IIB flux compactifications on six-dimensional SU(2)-structure manifolds with O5-and O7-planes. These six-dimensional spaces allow not only for F 3 and H 3 fluxes but also for F 1 and F 5 fluxes. We derive the four-dimensional N = 1 scalar potential for such compactifications and present one explicit example of a fully stabilized AdS vacuum with large volume and small string coupling. We then discuss cosmological aspects of these compactifications and derive several no-go theorems that forbid dS vacua and slow-roll inflation under certain conditions. We also study concrete examples of cosets and twisted tori and find that our no-go theorems forbid dS vacua and slow-roll inflation in all but one of them. For the latter we find a dS critical point with ǫ numerically zero. However, the point has two tachyons and eta-parameter η ≈ −3.1.
It is shown that the RR charges of Gepner models are not all accounted for by the usual tensor product and permutation branes. In order to characterise the missing D-branes we study the matrix factorisation approach to the description of D-branes for Gepner models. For each of the A-type models we identify a set of matrix factorisations whose charges generate the full lattice of quantised charges. The additional factorisations that are required correspond to generalised permutation branes.
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