JCAP study finds hidden dark-matter attraction can slow large-scale structure growth

A theoretical study in the Journal of Cosmology and Astroparticle Physics finds that an extra attractive force among dark matter particles would usually slow, not speed, the growth of large-scale cosmic structure, ScienceDaily reported from Sissa Medialab materials. Researchers modeled dark matter that feels a long-range force in addition to gravity. The force helps dark matter gather more efficiently, but the same process causes the particles to effectively lose mass over time, weakening their gravitational influence. In most cases the combined effect suppresses structure growth and does not leave a stronger imprint on the cosmic microwave background. Corresponding author Zachary Weiner of the Perimeter Institute for Theoretical Physics said what is known about dark matter so far comes only through gravitational effects, leaving room for hidden interactions ordinary matter cannot detect. ScienceDaily said interest in such a dark force has grown as precise measurements of expansion and clustering do not always align with the standard cosmological model. The authors note the mechanism may matter for more complicated models, including some proposed to address recent Dark Energy Spectroscopic Instrument measurements that involve similar dark-sector interactions. The paper is titled Dark forces suppress structure growth and carries DOI: 10.1088/1475-7516/2026/06/055.