Dark Matter Can’t Be Too Heavy

Dark matter may have to go on a diet, according to new research.

By now we have a vast abundance of evidence for the existence of dark matter. That’s because cosmological observations just aren’t adding up. All our measures of luminous matter fall far short of the total gravitational effects we see in galaxies, clusters, and the universe as a while.

Dark matter far outweighs the regular matter in the cosmos, but we still don’t know the identity of this mysterious particle. Because of that, it could have a wide variety of masses, anything from a billionth of the mass of the lightest known particles to mass ranges far, far heavier.

Most searches for dark matter have focused on masses roughly in the range of the heavier known particles, because several extensions to known physics predict particles like that. But those searches have thus far come up short, making physicists wonder if the dark matter might be much lighter than expected…or much heavier.

But heavier dark matter runs into some serious issues, according to a new paper appearing on the preprint server arXiv.

The problem is that we expect to dark matter to at least sometimes, rarely, interact with normal matter. In the extremely early universe, dark matter and regular matter talked to each other much more often. But as the cosmos expanded and cooled, the interactions broke down, freezing out dark matter and leaving it behind as a relic background.

Almost all models of dark matter predict that it talks to normal matter through some interaction involving the Higgs boson, the famous particle finally detected by the Large Hadron Collider in 2012. The Higgs boson is responsible for the mass of many particles.

But interactions in physics are two-way streets. Many particles acquire their mass through their interaction with the Higgs, and in turn the mass of the Higgs is modified by its interaction with the other particles. But those particles are so light that the back-reaction isn’t very strong, so usually we don’t have to worry about it.

But if the dark matter is much heavier, somewhere around ten times the mass of the heaviest known particles, then its own interactions will cause the Higgs to balloon up in mass, making it far heavier than measurements suggest.

There are possibilities to get around this restriction. The dark matter might not interact with regular particles at all, or through some exotic mechanism that doesn’t involve the Higgs. But those models are few are far between, and require a lot of fine-tuning and extra steps.

This means that the dark matter, whatever it is, might just be an ultra-light particle, rather than an ultra-heavy one.

The post Dark Matter Can’t Be Too Heavy appeared first on Universe Today.