Graceful exit from a stringy landscape via MSSM inflation

TL;DR

This paper proposes embedding MSSM inflation into the string landscape to resolve the graceful exit problem of old inflation and the fine-tuning issue, enabling natural reheating and a relaxing cosmological constant.

Contribution

It demonstrates how MSSM flat direction inflation can be integrated into the string landscape to address multiple issues in early universe cosmology.

Findings

MSSM inflation can be embedded in the string landscape.

Regions with favorable initial conditions for eternal inflation are generated.

Reheating into Standard Model particles is naturally achieved.

Abstract

The cosmological evolution of the string landscape is expected to consist of multiple stages of old inflation with large cosmological constant ending by tunnelling. Old inflation has a well known graceful exit problem as the observable universe becomes empty, devoid of any entropy. Simultaneously, in the quest for reheating the right degrees of freedom, it is important that the final stage of inflation reheat Standard Model sector. It is known that inflation can occur naturally along a flat direction of the Minimal Supersymmetric Standard Model (MSSM), solving the reheating problem, but the initial conditions require a large degree of fine-tuning. In this paper, we study how inflation of a MSSM flat direction can be embedded into the string theory landscape to solve both the graceful exit problem of old inflation and the fine-tuning problem of MSSM inflation, elaborating on ideas of Bousso and Polchinski. The fluctuations of the MSSM flat direction during old inflation create regions with initial conditions favorable for eternal inflation, which also allows the cosmological constant to continue to relax. This final phase of inflation also provides all the usual benefits of MSSM inflation, including straightforward reheating into Standard Model degrees of freedom.