Dark matter turned out to be more powerful than scientists had assumed

Physicists from the Perimeter Institute for Theoretical Physics investigated a hypothetical "dark force" — an additional interaction between dark matter particles acting alongside gravity — and arrived at an unexpected conclusion: its effect turned out to be the direct opposite of what theorists had predicted. The results of the work were published in the Journal of Cosmology and Astroparticle Physics (JCAP).

The very idea of the existence of such a force arose from puzzling contradictions between various cosmological measurements. In particular, the data from the DESI dark energy survey could not be reconciled with the observational results of cosmic microwave background clustering. A team of scientists led by Zachary Weiner constructed a detailed model showing how an additional attraction between dark matter particles could affect the formation of large cosmic structures.

The result turned out to be paradoxical. Yes, the "dark force" does indeed cause dark matter to cluster more efficiently. However, at the same time, it causes dark matter particles to effectively "lose mass" as the Universe expands, which significantly weakens their gravitational influence. Ultimately, the net effect more often suppresses rather than accelerates the growth of large-scale structures — contrary to initial expectations.

As the study's authors emphasize, the obtained result is of fundamental importance for dark energy models related to DESI data: any theory that allows for hidden self-interaction of dark matter must account for this effect of the "effective lightening" of particles during the expansion of the Universe.