Seeking de-Sitter Vacua in the String Landscape

Abstract: In this report, we present a concise review on the various moduli stabilisation schemes proposed in the context of type IIB superstring compactifications using Calabi-Yau orientifolds. We discuss the details of the known schemes by classifying them into two categories; the first one includes non-perturbative superpotential contributions leading to the well-known class of models like KKLT, Racetrack and LVS, while the second one includes only perturbative corrections arising from the series of $\alpha^\prime$- and string-loop effects, leading to a new scheme - known as perturbative LVS. In addition, we motivate and briefly discuss about the global embedding requirements for all these moduli stabilisation schemes, and present some details for the perturbative LVS scheme by focusing on a concrete CY orientifold setting. In this context, the resulting 4D effective supergravity model indeed does not receive any non-pertubative superpotential effects due to the lack of necessary divisor topologies, and the K\"ahler moduli stabilisation is performed entirely by perturbative effects, leading to AdS minimum with exponentially large VEV for the overall volume of the internal CY manifold. It is further shown how this class of AdS solutions can be uplifted to de-Sitter solutions by using a couple of prescriptions such as $D$-term uplifting and the $T$-brane uplifting.