A Smolin-like branching multiverse from multiscalar-tensor theory

TL;DR

This paper introduces a multiscalar-tensor theory modeling a branching multiverse with scalar fields that can mimic dark matter and reproduce Newtonian gravity, offering a new framework for multiverse and gravity research.

Contribution

It develops a novel multiscalar-tensor model with a branching multiverse structure, incorporating scalar fields that emulate dark matter and exhibit unique screening properties.

Findings

The model reproduces Newtonian gravity in the appropriate limit.

Scalar fields act as dark matter candidates with active decoupling.

Stability conditions for the multiscalar system are established.

Abstract

We implement a Smolin-like branching multiverse through a directed, acyclic graph of $N$ metrics. Our gravitational and matter actions are indistinguishable from $N$ decoupled statements of General Relativity, if one varies with respect to metric degrees of freedom. We replace $N-1$ metrics with scalar fields by conformally relating each metric to its unique graph predecessor. Varying with respect to the $N-1$ scalar fields gives a multiscalar-tensor model which naturally features dark matter candidates. Building atop an argument of Chapline and Laughlin, branching is accomplished with the emergence of order parameters during gravitational collapse: we bootstrap a suitably defined $N$ scalar field model with initial data from an $N-1$ field model. We focus on the nearest-neighbour approximation, determine conditions for dynamical stability, and compute the equations of motion. The model features a novel screening property where the scalar fields actively adjust to decouple themselves from the stress, oscillating about the requisite values. In the Newtonian limit, these background values for the scalar fields exactly reproduce Newton's law of gravitation.