Particle dark matter versus modified gravity

Abstract

There are at least two possible solutions to the so-called Dark Matter problem. One is to introduce new particles and another one is to modify gravity. In these proceedings of the 182nd Nobel Symposium on dark matter, I question the particle dark matter hypothesis in light of new developments in the gravity sector. To this effect, I review how the CMB anisotropies and the details of structure formation have been used to test the dark matter microscopic properties. I explain how this has led to challenge the Hut-Lee & Weinberg argument and the introduction of light (thermal) dark matter scenarios and dark photon/light Z′. These developments have ultimately paved the way for a comprehensive exploration of the entire dark matter mass spectrum. I then discuss a new theory of modified gravity that appears to be a novel alternative to particle dark matter and ask the question: how to distinguish the two? I expect this question to become extremely relevant in absence of dark matter particle detection in Earth based experiments and in presence of ambiguous astrophysical and cosmological signals.