Conflicts with de Sitter Vacua in Superstring Theory

Abstract

Models of our universe lack consistency at different energy scales, so we require a theory with ultraviolet (UV) completion such as string theory. A suitable candidate to model our universe in this framework is de Sitter space, a spacetime which expands and has positive curvature. When describing the expansion of this space, however, one computes the wrong sign for the cosmological constant that would not allow for an expanding universe. This motivates one to consider corrections from a quantum theory to reproduce the correct positive sign for the cosmological constant. The conditions that cause this incorrect sign are known as the \textit{swampland criteria}, and prevent de Sitter space from being realized in a consistent manner at different energy scales. We look at a framework to avoid the swampland restriction in a UV-complete theory by considering de Sitter space resulting from compactifications of type IIB superstring theory. In particular, we demonstrate that the definitions of particles in an expanding UV-incomplete theory leads to inconsistencies in the definition of the de Sitter vacuum states. Furthermore, we review previous attempts to prevent these inconsistencies by constructing coherent states that expand and have the desired de Sitter isometries over supersymmetric Minkowski space. These states add quantum corrections to the metric operator, resulting in the cosmological constant carrying the correct sign. Therefore, the de Sitter space can be used in a UV-complete theory to model our universe.