Dark matter interactions may be a hidden “dark force,” unexpectedly constraining our Universe’s expansion and structural development, according to researchers.
In a recent paper published in the Journal of Cosmology and Astroparticle Physics, researchers identified unexpected effects arising from dark matter particles interacting with one another and clustering via a hidden dark force.
Typically, scientists can only study the invisible—and still purely theoretical—dark matter through its gravitational effects on ordinary matter. However, the new research explores how dark matter may also influence itself.
Exploring the Dark Force
As scientific instruments become more precise, researchers continue to uncover mysteries once hidden at the fuzzy edges of our understanding of the cosmos. One such puzzle involves discrepancies in measurements of the Universe’s density over time. Within the widely accepted ΛCDM model of cosmology, observations of cosmic expansion and the growth of large-scale structures have not always aligned with theoretical expectations.
To address these tensions, researchers have proposed a theoretical dark force—a previously unrecognized attractive force that acts only between dark matter particles. Such a force could influence both the expansion of the Universe and the formation of cosmic structures, potentially helping reconcile current models with recent observations.
“What we really know about dark matter has so far been learned only through its gravitational effects,” said co-author Zachary Weiner, a researcher at the Perimeter Institute for Theoretical Physics. “That leaves open the possibility that dark matter might have additional interactions that are hidden from ordinary matter.”
Investigating the Dark Force
The researchers examined models in which dark matter particles interact through a long-range force beyond gravity. By combining cosmological observations with theoretical calculations, they searched for evidence of how such a force might affect both the growth of cosmic structures and the expansion history of the Universe.
At first glance, the prediction seemed straightforward: if an additional attractive force pulls dark matter particles together, it should enhance their ability to cluster, potentially explaining why some observations suggest a denser cosmic landscape than expected.
“The first thing you would expect is that giving dark matter an additional attractive force should make structures grow faster,” Weiner explained. “But another effect comes into play at the same time.”
A Surprising Discovery
The researchers’ results revealed a more complicated picture. While a dark force does cause dark matter to cluster more efficiently, it also alters the expansion of the Universe in a way that causes dark matter particles to become effectively lighter over time.
As a result, the additional clustering is not strong enough to significantly increase matter’s gravitational imprint on the cosmic microwave background. Instead, the net effect is to suppress the overall growth of cosmic structure.
According to the researchers, this previously unrecognized interaction could play an important role in new cosmological models developed to explain observations from the Dark Energy Spectroscopic Instrument (DESI) in Tucson, Arizona. If confirmed, the effects of a dark force may need to be incorporated into future efforts to understand the evolution of the Universe.
As astronomers peer farther into space and deeper into cosmic history with ever-greater precision, studies like this may help explain subtle discrepancies that have long remained hidden.
“The Universe is often more subtle than our intuition,” Weiner concluded. “That’s exactly why we have to keep testing these ideas.”
The paper, “Dark Forces Suppress Structure Growth,” appeared in the Journal of Cosmology and Astroparticle Physics on June 22, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.