Avoiding Boltzmann Brain domination in holographic dark energy models

TL;DR

This paper investigates whether holographic dark energy models can avoid domination by Boltzmann Brains, finding parameter conditions that prevent such paradoxes while considering observational constraints.

Contribution

It analyzes both local and global perspectives of holographic dark energy models to identify parameter regimes that prevent Boltzmann Brain domination.

Findings

Parameter c outside a narrow range avoids BB domination in local view.

Global view imposes stricter bounds on c, conflicting with observational bounds.

Models can be BB-safe if parameters are carefully chosen.

Abstract

In a spatially infinite and eternal universe approaching ultimately a de Sitter (or quasi-de Sitter) regime, structure can form by thermal fluctuations as such a space is thermal. The models of Dark Energy invoking holographic principle fit naturally into such a category, and spontaneous formation of isolated brains in otherwise empty space seems the most perplexing, creating the paradox of Boltzmann Brains (BB). It is thus appropriate to ask if such models can be made free from domination by Boltzmann Brains. Here we consider only the simplest model, but adopt both the local and the global viewpoint in the description of the Universe. In the former case, we find that if a parameter $c$, which modulates the Dark Energy density, lies outside the exponentially narrow strip around the most natural $c = 1$ line, the theory is rendered BB-safe. In the later case, the bound on $c$ is exponentially stronger, and seemingly at odds with those bounds on $c$ obtained from various observational tests.