Hot Dark Matter Birth Could Reshape Cosmic Evolution Theories

New research challenges the long-held assumption that dark matter must be cold at birth, suggesting it could have originated as hot particles during the post-inflationary reheating phase of the universe.

This finding, published in Physical Review Letters (November 2023), proposes that dark matter decoupled from ordinary matter while still hot, then cooled sufficiently to function like cold dark matter, enabling galaxy formation.

The study, led by teams from the University of Minnesota and Université Paris-Saclay, introduces a mechanism where dark matter particles—initially moving at relativistic speeds—slow down over time, aligning with the Lambda Cold Dark Matter (LCDM) model’s predictions for structure formation.

"Dark matter can be red hot when it is born, but still have time to cool down before galaxies begin to form," the authors state. This cooling process, they argue, reconciles the tension between hot dark matter’s rapid motion and the observed large-scale structure of the universe.

Neutrinos, previously dismissed as hot dark matter candidates due to their inability to clump effectively, are now being reconsidered under this framework. If produced during the reheating phase of the Big Bang, their properties might align with the study’s hypothesis.

The team emphasizes that experiments at particle accelerators and observations of the early universe will be critical for testing these ideas. However, the study does not claim to replace LCDM outright but rather to expand its parameter space by incorporating time-dependent cooling effects.