# Distinguishing cosmologies using the turn-around radius near galaxy clusters

## TL;DR

This study investigates the potential of using the turn-around radius around galaxy clusters to constrain cosmological models, accounting for environmental complexities and measurement uncertainties through numerical simulations.

## Contribution

It quantifies realistic error-bars in measuring the turn-around radius and assesses its effectiveness in distinguishing between standard and alternative cosmological models.

## Key findings

- Error-bars are typically around 20% for b4b5CDM cosmology.
- Only extreme dark energy models can be distinguished from b4b5CDM given current measurement uncertainties.
- Environmental effects significantly impact the precision of turn-around radius measurements.

## Abstract

Outside galaxy clusters the competition between the inwards gravitational attraction and the outwards expansion of the Universe leads to a special radius of velocity cancellation, which is called the turn-around radius. Measurements of the turn-around radius hold promises of constraining cosmological parameters, and possibly even properties of gravity. Such a measurement is, however, complicated by the fact that the surroundings of galaxy clusters are not spherical, but instead are a complicated collection of filaments, sheets and voids. In this paper we use the results of numerically simulated universes to quantify realistic error-bars of the measurement of the turn-around radius. We find that for a $\Lambda$CDM cosmology these error-bars are typically of the order of $20\%$. We numerically simulate three different implementations of dark energy models and of a scalar dark sector interaction to address whether the turn-around radius can be used to constrain non-trivial cosmologies, and we find that only rather extreme models can be distinguished from a $\Lambda$CDM universe due to the large error-bars arising from the non-trivial cluster environments.