Dark matter could be a "cosmic relic" of other dimensions of space-time

Despite exhausting decades of research and experiments, the mystery of dark matter has not yet been solved. We know that it must exist, and in much greater quantities than ordinary matter - many indirect observations tell us - but we are not sure how it is made nor have we ever been able to observe it experimentally. Today, a team of physicists from the Institut de Physique des 2 Infinis (IP2I) of the French CNRS, the University of Lyon and Korea University, including the Italian Giacomo Cacciapaglia, published a study that corroborates the hypothesis according to which the dark matter particles could coincide with the gravitons (the hypothetical mediators of the gravitational force, also never observed experimentally) produced during the early life stages of the Universe. The work was published in Physical Review Letters.

Why it is important to look for dark matter At the moment, the most reliable theoretical framework for describing the behavior of particles and known forces, the so-called Standard Model, appears to be incomplete. Several experimental observations, in fact, suggest that alongside ordinary matter - the one described, precisely, by the equations of the Standard Model - there must also exist another type of matter, a sort of "invisible component" that interacts only through gravitational force . "Observing the speed of rotation of stars around galaxies and studying the cosmic background radiation - explains Cacciapaglia to sportsgaming.win - we realized, long ago, that there must necessarily be something else besides ordinary matter. And that's what we call, precisely, dark matter ". Always according to what we know so far, it is estimated that for every proton, neutron or other particle of ordinary matter, there must be at least five of dark matter; in other words, dark matter should make up about 85% of all matter in the Universe, and about 27% of its total energy.

Who are particles and how are they made, then? of dark matter? Over the course of history we have formulated and tested various hypotheses: “Before we thought they were neutrinos - continues Cacciapaglia - but today we know that this cannot be the case. The most popular candidates are the so-called Wimp [Weakly interactive massive particles, or "weakly interacting massive particles"], heavy particles that interact very little with each other ". How little? If you had a huge lead cube with edges 200 light years long, a single dark matter particle would have a 50% chance of passing through it without interacting with anything. And this could be one of the reasons why, despite the highly sophisticated tools we currently have at our disposal, it is still very difficult to observe dark matter directly.

Another possibility There is also the hypothesis examined by Cacciapaglia and colleagues, according to which the dark matter particles, in reality, are not the Wimp, but even less interacting entities, the so-called Fimp (Feebly interactive massive particles, or "weakly interacting massive particles"). "The Fimp model - says Cacciapaglia - provides for a different mechanism for the production of dark matter compared to the Wimp model: in the latter, ordinary matter, in the first moments of life of the Universe, would have been in thermal equilibrium with dark matter , and the two entities would have 'decoupled' upon cooling; in the Fimp model, on the other hand, dark matter is the result of collisions between hot particles of ordinary matter ".

The role of gravity According to the calculations of the authors of the study just published, gravitons could be hidden behind the Fimp , massive particles created in the first moments of life of the Universe. "Until now - explains Cacciapaglia - this hypothesis was not considered credible, because the number of gravitons produced seemed to be too low to give rise to the amount of dark matter that we think there is today in the Universe. Our calculations, on the other hand, show that the number of gravitons is actually much higher, particularly by a factor of 12. And this number is consistent with the amount of dark matter ”. The theory behind the calculations is quite exotic, and predicts the existence of extra dimensions with respect to the three spatial dimensions and time: propagating in these extra dimensions, gravity would then "materialize" in the Universe in the form of massive gravitons, which would interact very weakly with ordinary matter. It is an interesting hypothesis, among other things, because it refers to already known interactions (gravitational ones, precisely) and does not provide for the introduction of unknown interactions. Now we need to think about how to verify it: "There are two ways - concludes Cacciapaglia - Gravitons, or Fimp, decay producing photons that have a very specific energy. We could try to look for photons of this type: if we found them we would have proof of the existence of a mechanism of this type. Another possibility, at the most remote moment, is to try to produce gravitons in the laboratory, with a particle accelerator. At the moment the accelerators we have available do not reach sufficient energy, but a machine built ad hoc could do it ".