SIMP v WIMP: Novel thermal relic mechanism for dark matter creation in the early universe
(Phys.org)—Our current understanding of the universe is that the majority of its mass consists of dark matter (DM) – but there's a wrinkle: Despite having an idea about some of its properties – dark matter is cold, massive, has neither color nor electrical charge, and does not self-interact very strongly, so that it is detected through its gravitational interactions with ordinary matter and radiation – scientists don't know what dark matter actually is. That said, and as might well be expected, dark matter theories abound, one being that dark matter is a thermal relic from the early universe, in which all particles are in thermal equilibrium until expansion and cooling occurs. At that point, particle interaction rates slow, causing them to freeze-out – and while unstable particles vanish, stable particles reach what's known as their thermal relic density that remains. In this scenario, the most promising dark matter candidates are...