Multi-component DHOST analysis in galaxy clusters

TL;DR

This study tests a modified gravity theory called DHOST in galaxy clusters, finding it can better explain some observations related to dark energy but is less favored when considering dark matter effects.

Contribution

It provides the first observational analysis of DHOST theories in galaxy clusters using combined X-ray and lensing data, exploring both dark energy and dark matter scenarios.

Findings

DHOST model mildly favored over GR for dark energy description.

DHOST alleviates mass estimate discrepancies in galaxy clusters.

Model disfavored when considering dark matter effects.

Abstract

Extended Theories of Gravity with additional scalar degrees of freedom have recently acquired increasing interest due to the presence of a screening mechanism that allows suppressing at small scales (e.g., the Solar System scale) every modification restoring General Relativity. In this work, we consider a second-order Extended Theory of Gravity belonging to the family of Degenerate High Order Scalar Tensor theories (DHOST) characterized by a partial breaking of the Vainshtein screening mechanism. We study this model in two different scenarios as a description of dark energy only and as a description of both dark matter and dark energy. Such scenarios have been tested here by analysing a sample of 16 high-mass galaxy clusters targeted by the Cluster Lensing and Supernova survey with Hubble (CLASH) program using two complementary probes, namely X-ray and strong-and-weak gravitational lensing observations. In mass modelling, we adopt a multi-component approach including hot gas and galactic stellar contributions. For the majority of the clusters in our sample, results show mild Bayesian evidence in favour of the DHOST model as a description of dark energy over General Relativity. This model also appears to alleviate the discrepancy present in General Relativity between X-ray hydrostatic and lensing mass estimates. For the second scenario where gravity acts as both dark energy and dark matter due to the partial breaking of the Vainshtein screening mechanism at cluster scales, the model is statistically disfavoured compared to General Relativity.