Measures on transitions for cosmology from eternal inflation

TL;DR

This paper develops measures for counting transitions between vacua in eternal inflation, emphasizing the importance of transition histories over vacuum counts for predicting cosmological observables.

Contribution

It introduces new measures for counting vacuum transitions, crucial for making predictions in eternal inflation scenarios with slow-roll inflation.

Findings

Transition-based measures differ from vacuum-based measures.

Predictions depend on the history after the last vacuum transition.

The approach clarifies how to connect landscape measures with observable predictions.

Abstract

We argue that in the context of eternal inflation in the landscape, making predictions for cosmological -- and possibly particle physics -- observables requires a measure on the possible cosmological histories as opposed to one on the vacua themselves. If significant slow-roll inflation occurs, the observables are generally determined by the history after the last transition between metastable vacua. Hence we start from several existing measures for counting vacua and develop measures for counting the transitions between vacua.