Effective upliftings in Large volume compactifications

TL;DR

This paper reviews mechanisms for achieving de Sitter or Minkowski vacua in type-IIB string compactifications, proposing a criterion based on the small variation of uplifting terms and exploring a novel dilaton-dependent uplifting approach.

Contribution

It introduces a new criterion for effective uplifting in large volume scenarios and proposes a novel dilaton-dependent uplifting mechanism for obtaining dS vacua.

Findings

Uplifting terms with $V_{up} \\sim 1/\\mathcal{V}^\\gamma$ should satisfy $\\gamma^2 \\ll 12$.

The proposed dilaton-dependent uplifting can achieve dS vacua.

The criterion explains why previous models failed to uplift successfully.

Abstract

After reviewing several mechanisms proposed to get a dS/Minkowski vacuum in moduli stabilization scenarios of type-IIB superstring orientifold compactifications we propose a criterium for characterizing those that may effectively lead to a positive small cosmological constant. We suggest that the variation in the expectation value of a good uplifting term, due to the shift in the minimum of the potential after uplifting, is much smaller than the original cosmological constant. This is studied with some detail in Large volume scenarios where the dependency on the volume direction is rather generic and easy to spot. Here we find that an uplifting term in the potential, with generic form $V_{up}\sim 1/{\cal V}^\gamma$, should be restricted to the one satisfying $\gamma^2\ll 12$. Such a bound might explain why in models previously studied no uplifting has been achieved, and gives motivations to study a novel proposal of dilaton dependent uplifting mechanism for which no numerical studies has been performed before. We find that in this case it is actually possible to get a dS vacuum, but still leave open the question of a more precise discrimination feature the good uplifting mechanisms should satisfy.