Negative vacuum energy densities and the causal diamond measure

TL;DR

This paper examines how the causal diamond measure predicts vacuum energy densities in the string landscape, revealing it poorly fits observations when negative values are considered, with most observers measuring smaller or negative densities.

Contribution

It analyzes the implications of negative vacuum energy densities on the causal diamond measure's predictive success in the string landscape.

Findings

Causal diamond measure predicts a poor fit to observed vacuum energy densities with negative values.

Most observers in the landscape measure smaller or negative vacuum energies than ours.

The measure's predictions are significantly affected by the inclusion of negative vacuum energy densities.

Abstract

Arguably a major success of the landscape picture is the prediction of a small, non-zero vacuum energy density. The details of this prediction depends in part on how the diverging spacetime volume of the multiverse is regulated, a question that remains unresolved. One proposal, the causal diamond measure, has demonstrated many phenomenological successes, including predicting a distribution of positive vacuum energy densities in good agreement with observation. In the string landscape, however, the vacuum energy density is expected to take positive and negative values. We find the causal diamond measure gives a poor fit to observation in such a landscape -- in particular, 99.6% of observers in galaxies seemingly just like ours measure a vacuum energy density smaller than we do, most of them measuring it to be negative.