The Swampland, Quintessence and the Vacuum Energy

TL;DR

This paper examines the challenges of implementing quintessence models with varying couplings in quantum theories, highlighting issues with quantum corrections and proposing potential resolutions.

Contribution

It analyzes the quantum correction problems in quintessence models with varying parameters and suggests conditions for their consistent realization in quantum theories.

Findings

Varying couplings in quintessence models face severe quantum correction issues.

Achieving consistency requires fine-tuning, unknown cancellation mechanisms, or coupling only to very light states.

Quantum corrections can destabilize the effective potential in these models.

Abstract

It has recently been conjectured that string theory does not admit de Sitter vacua, and that quintessence explains the current epoch of accelerated cosmic expansion. A proposed, key prediction of this scenario is time-varying couplings in the dark sector, induced by the evolving quintessence field. We note that cosmological models with varying couplings suffer from severe problems with quantum corrections, beyond those shared by all quintessence models. The vacuum energy depends on all masses and couplings of the theory, and even small variations of parameters can lead to overwhelmingly large corrections to the effective potential. We find that quintessence models with varying parameters can be realised in consistent quantum theories by either: 1) enforcing exceptional levels of fine-tuning; 2) realising some unknown mechanism that cancels all undesirable contributions to the effective potential with unprecedented accuracy; or 3) ensuring that the quintessence field couples exclusively to very light states, and does not backreact on heavy fields.