The Cosmological Constant and the String Landscape

TL;DR

This paper reviews theories of the cosmological constant, focusing on fixed versus adjustable vacuum energy, and examines the string landscape as a potential adjustment mechanism with future research directions.

Contribution

It provides a comparative analysis of fixed and adjustable vacuum energy theories and evaluates the string landscape as a novel adjustment mechanism.

Findings

The string landscape offers a possible explanation for the small value of the cosmological constant.

Challenges remain in understanding the dynamics and selection of vacua in the landscape.

Future research directions include exploring the viability and implications of the landscape mechanism.

Abstract

Theories of the cosmological constant fall into two classes, those in which the vacuum energy is fixed by the fundamental theory and those in which it is adjustable in some way. For each class we discuss key challenges. The string theory landscape is an example of an adjustment mechanism. We discuss the status of this idea, and future directions.