Indistinguishability of Warm Dark Matter, Modified Gravity, and Coupled Cold Dark Matter

TL;DR

This paper demonstrates that warm dark matter, modified gravity, and coupled cold dark matter models are indistinguishable using standard cosmological observations, highlighting the need for alternative probes to differentiate them.

Contribution

It reveals the degeneracy among WDM, modified gravity, and coupled CDM models in cosmological observations, emphasizing the necessity for new methods to distinguish these theories.

Findings

WDM, modified gravity, and coupled CDM are indistinguishable with current cosmological data.

Standard expansion and growth history observations cannot differentiate these models.

Additional observational probes are required to break the degeneracy.

Abstract

The current accelerated expansion of our universe could be due to an unknown energy component with negative pressure (dark energy) or a modification to general relativity (modified gravity). On the other hand, recently warm dark matter (WDM) remarkably rose as an alternative of cold dark matter (CDM). Obviously, it is of interest to distinguish these different types of models. In fact, many attempts have been made in the literature. However, in the present work, we show that WDM, modified gravity and coupled CDM form a trinity, namely, they are indistinguishable by using the cosmological observations of both cosmic expansion history and growth history. Therefore, to break this degeneracy, the other complementary probes beyond the ones of cosmic expansion history and growth history are required.