Dark Matter Is Born from Ghostly Neutrinos express
Visible matter is a drop in the sea of cosmic soup. The foundation of the Universe is made of invisible dark matter, whose gravity keeps galaxies from flying apart. The best candidate for this role is sterile neutrinos, ghost particles connected to us only by the thinnest of bridges.
Immediately after the Big Bang, space suddenly expanded and became extremely hot. A new model shows: if a tiny fraction of that energy went into creating sterile neutrinos, exactly enough were born to explain all dark matter.
The mechanism solves the mystery of the weak signal from neutrinos, bypassing the limitations of telescopes. Now dark matter becomes a tool: future observatories will be able to measure the temperature of that 'cooking,' peering into the first moments after the Big Bang.
Original abstract
as written by the authors arXiv:2601.03346v2
Sterile neutrinos offer a minimal and testable explanation for dark matter (DM), with their radiative decay actively searched for in X-ray observations. We show that cold sterile neutrino DM can be efficiently produced during reheating from inflaton decays with a small branching ratio, $${\rm BR}\lesssim 10^{-4}$$. This production mechanism opens regions of parameter space where the active-sterile mixing is small enough to evade current X-ray constraints while reproducing the observed DM abundance. We systematically map the viable parameter space in terms of the sterile neutrino mass, mixing angle, inflaton mass, reheating temperature, and branching ratio. We further demonstrate that sterile neutrino DM can serve as a probe of inflationary reheating, with future X-ray observations capable of yielding information on the inflaton mass and the reheating-temperature ratio $$m_\phi/T_{\rm rh}$$. For a given inflationary model in which the inflaton mass is known, this leads to a lower bound on the reheating temperature that is several orders of magnitude stronger than the existing bound from Big Bang Nucleosynthesis.
Sterile neutrinos are so elusive that they could fly through a light-year of lead without ever colliding with an atom.