# Cosmological constant: relaxation vs multiverse

## TL;DR

This paper explores a scalar field with a bottomless potential, analyzing how its dynamics can lead to a multiverse with a small cosmological constant, potentially resolving some anthropic selection issues.

## Contribution

It introduces a model where rebounces in scalar field cosmology can select for small vacuum energy, offering a new perspective on the cosmological constant problem.

## Key findings

- Rebounce dynamics can avoid singularities in scalar field cosmologies.
- Probabilities in the multiverse can be better defined without usual ambiguities.
- The model predicts a small cosmological constant more naturally than standard anthropic arguments.

## Abstract

We consider a scalar field with a bottom-less potential, such as $g^3 \phi$, finding that cosmologies unavoidably end up with a crunch, late enough to be compatible with observations if $g \lesssim 1.2 H_0^{2/3} M_{\rm Pl}^{1/3}$. If rebounces avoid singularities, the multiverse acquires new features; in particular probabilities avoid some of the usual ambiguities. If rebounces change the vacuum energy by a small enough amount, this dynamics selects a small vacuum energy and becomes the most likely source of universes with anthropically small cosmological constant. Its probability distribution could avoid the gap by 2 orders of magnitude that seems left by standard anthropic selection.