Vorschau

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Abstract

We analyze whether a D7-brane position modulus in Type IIB string compactifications can be a suitable inflaton candidate. To this end, we study two rather different scenarios: In the first, the inflaton is associated with the distance of two D7-branes. Inflation is driven by a brane-flux-induced D-term energy and proceeds as the branes approach each other. It ends in a tachyonic instability. This model thus represents a string-theoretic version of D-term hybrid inflation. In the second model, the inflaton is the position modulus of a single D7-brane. During inflation this modulus traverses a large distance in Planck units. This is possible due to a monodromy in field space. The brane displacement leads to a continuously changing F-term energy which drives (chaotic) inflation. We explicitly analyze the intricate interplay of each scenario with moduli stabilization. In particular, since Kähler moduli are fixed by higher-order terms in the scalar potential, their masses are typically relatively small. We demonstrate that, nonetheless, in our models the inflaton potential does not upset Kähler moduli stabilization. Finally, we show that both models can be in agreement with the most recent cosmological observations, while their implications for the size of the tensor-to-scalar ratio are very different.