Dark matter force could curb cosmic structure growth, study finds
A new cosmology study says a hidden force between dark matter particles would often slow, rather than accelerate, large-scale structure growth.
By Priya Raghavan · Science Reporter
3 min read
A proposed force acting only between dark matter particles may reduce the growth of cosmic structures instead of making them form faster, according to a new study. The finding matters because physicists have been testing whether unseen dark matter interactions could help explain small mismatches among leading observations of the universe.
The research, published in the Journal of Cosmology and Astroparticle Physics, examined theoretical models in which dark matter feels a long-range force in addition to gravity. The study was led by Marco Costa and colleagues, with Zachary Weiner of the Perimeter Institute for Theoretical Physics identified as corresponding author by SISSA Medialab.
Dark matter is usually treated as matter that reveals itself through gravity while remaining invisible to light and ordinary particle interactions. Weiner said researchers know dark matter through its gravitational effects, leaving room for the possibility that it has other interactions hidden from ordinary matter.
Why physicists are testing dark forces
The work addresses a live question in cosmology: whether the standard model of the universe is missing a component that could account for mild observational tensions. SISSA Medialab reported that measurements of cosmic expansion over time and measurements of the growth of galaxies and large-scale structure do not line up perfectly in some analyses.
Some observations of the distant universe suggest expansion may have been a little slower in the past than the standard cosmological model predicts, according to the report. Other measurements, including those tied to the cosmic microwave background, have hinted that matter may be more strongly clustered across the largest scales than expected.
A hidden dark matter force has been one candidate explanation. If dark matter particles attract each other through such a force, the simple expectation is that they would gather into clumps more efficiently, potentially affecting both the universe’s expansion history and the formation of cosmic structure.
A result that runs against first expectations
Weiner said the initial expectation is straightforward: an extra attractive force should make structures grow faster. But, he added, a second effect appears at the same time in the models studied.
According to the researchers, the added force does increase dark matter clustering locally in the model. At the same time, the mechanism changes how dark matter evolves as the universe expands, making the particles effectively lighter over time.
That change weakens the overall gravitational effect of matter, the study found. As a result, the extra attraction is generally outweighed, and the net effect is usually to suppress the growth of structure rather than enhance it.
The researchers said this result also bears on some models proposed in connection with recent observations from the Dark Energy Spectroscopic Instrument, known as DESI. Those models can rely on similar dark matter interactions, and the study’s mechanism may apply to many of those more elaborate scenarios as well.
Future surveys and observatories are expected to produce more precise cosmological data, giving researchers tighter tests of dark matter models. Weiner said the universe often behaves more subtly than intuition suggests, which is why these ideas need continued testing.
This story draws on original reporting from Phys.org.