Predicting the cosmological constant with the scale-factor cutoff measure

TL;DR

This paper investigates how a scale-factor cutoff measure in multiverse models influences the predicted distribution of the cosmological constant, aligning well with observations and suppressing larger-than-observed values.

Contribution

It introduces a simple multiverse model with a scale-factor cutoff to regulate spacetime volume, providing predictions for Lambda that match observations.

Findings

The scale-factor cutoff suppresses large Lambda values beyond ten times the observed.

Predicted distribution of Lambda aligns with observational data.

Discusses implications for curvature and density contrast distributions.

Abstract

It is well known that anthropic selection from a landscape with a flat prior distribution of cosmological constant Lambda gives a reasonable fit to observation. However, a realistic model of the multiverse has a physical volume that diverges with time, and the predicted distribution of Lambda depends on how the spacetime volume is regulated. We study a simple model of the multiverse with probabilities regulated by a scale-factor cutoff, and calculate the resulting distribution, considering both positive and negative values of Lambda. The results are in good agreement with observation. In particular, the scale-factor cutoff strongly suppresses the probability for values of Lambda that are more than about ten times the observed value. We also discuss several qualitative features of the scale-factor cutoff, including aspects of the distributions of the curvature parameter Omega and the primordial density contrast Q.