Darkish matter cannot be too heavy or it would break our greatest mannequin of the universe, new analysis suggests.
We have now an abundance of proof that one thing fishy is going on within the universe. Stars orbit inside galaxies far too rapidly. Galaxies transfer round inside clusters a lot too quick. Buildings develop and evolve too quickly. If we depend solely the matter we will see, there merely is not sufficient gravity to elucidate all of those behaviors.
The overwhelming majority of cosmologists consider all of those phenomena might be defined via the presence of darkish matter, a hypothetical type of matter that’s huge, electrically impartial and hardly, if ever, interacts with regular matter. This darkish matter makes up a lot of the mass within the universe, far outweighing the quantity of luminous matter.
The id of darkish matter stays a thriller, as experiments designed to detect a stray, uncommon collision have failed to show up something. However these experiments have targeted on concentrating on a selected mass vary: roughly 10 to 1,000 giga-electron volts (GeV). (A GeV is equal to 1 billion electron volts.) That is within the vary of the heaviest recognized particles, just like the W boson and the highest quark. For many years, theorists favored this mass vary as a result of a number of easy extensions of the Normal Mannequin of particle physics predicted the existence of such particles.
As a result of we have not discovered something but, although, we have began to marvel if darkish matter is perhaps lighter or heavier than we thought. However heavier darkish matter runs into some critical points, in line with a brand new paper printed to the preprint database arXiv.
The issue is that darkish matter does generally work together with regular matter, if solely hardly ever. However within the early universe, when the cosmos was a lot hotter and denser, these interactions have been rather more frequent. Finally, because the universe expanded and cooled, these interactions slowed after which stopped, main the darkish matter to “freeze out” and stay silent within the background.
Whereas there are various, many fashions of potential darkish matter candidates, many work together with common particles via exchanges involving the Higgs boson — a basic particle that interacts with nearly all different particles and, via these interactions, imbues these particles with mass.
We all know the mass of the Higgs boson: round 125 GeV. The researchers discovered that this mass places a basic higher restrict on the attainable mass of most darkish matter candidates.
The issue is that every one interactions in physics are two-way streets. The Higgs talks to each darkish matter and common matter and, in lots of fashions, mediates interactions between them. However each sorts of matter additionally discuss again to the Higgs. These interactions seem as slight modifications to the Higgs boson’s mass.
For Normal Mannequin particles, we will calculate these corrections and suggestions interactions, which is how theorists predicted the mass of the Higgs boson nicely earlier than it was detected.
The researchers discovered that if the darkish matter particle had a mass better than a number of thousand GeV, its contribution to the Higgs mass could be extremely necessary, driving it away from its noticed worth. And since the Higgs is so central to figuring out many different basic physics, it will primarily shut down particle interactions altogether.
There are potentialities to get round this restriction, nonetheless. Darkish matter won’t work together with common particles in any respect, or the interplay would possibly occur via some unique mechanism that does not contain the Higgs. However these fashions are few and much between and require a number of fine-tuning and further steps.
Or it could possibly be that darkish matter is lighter than we thought. If we do not suppose heavy darkish matter is a viable candidate, then as we proceed to study this mysterious element of the universe, we will as an alternative focus our efforts within the different route. There has already been a surge of curiosity in axions, ultralight particles which might be predicted in some particle physics fashions and is perhaps a viable darkish matter candidate.
On the experimental aspect, if this result’s confirmed and holds to be a widespread restriction on darkish matter particle mass, we will refine and redesign our experiments to seek for low-mass, as an alternative of high-mass, particles.
