Comparing the motion of dark matter and standard model particles on cosmological scales

Comparing the Motion of Dark Matter and Standard Model Particles on Cosmological Scales

Dark matter has never been directly detected, leaving its interactions and behavior largely unknown. This study compares the movement of dark matter with that of standard matter particles on cosmological scales, aiming to constrain the strength of any additional fifth force acting on dark matter.

Background

It is commonly assumed that dark matter interacts only gravitationally with itself and standard model particles, meaning its motion follows Euler’s equation. However, until now, this assumption has not been directly tested at cosmological scales.

Methodology

The authors combine measurements of galaxy velocities with observations of gravitational potential wells, represented by the Weyl potential, to test how dark matter moves within these structures.

Findings

The data at redshifts between 0.3 and 0.8 are consistent with Euler’s equation governing dark matter motion.
Constraints on a hypothetical fifth force show that a positive fifth force cannot exceed 7% of the gravitational strength.
A negative fifth force is constrained to a maximum of 21% of gravitational strength.

"We find that current data are consistent with Euler’s equation at redshifts z ∈ [0.3, 0.8], and we place constraints on the strength of a potential fifth force, which would alter the way dark matter particles fall."

Future Prospects

Upcoming surveys, such as the Legacy Survey of Space and Time at the Vera C. Rubin Observatory and the Dark Energy Spectroscopic Instrument, are expected to significantly tighten these constraints, potentially detecting deviations from pure gravitational interaction as small as 2%.

"The coming generation of surveys ... will drastically improve the constraints, allowing to constrain a departure from pure gravitational interaction at the level of 2%."

Author's summary: Current observations confirm dark matter's motion aligns with gravitational theory, limiting any extra force acting on it to less than 7%, with future surveys poised to refine these bounds sharply.

Nature — 2025-11-04