Dark matter and ordinary matter ‘talk’ to each other

(ORDO NEWS) — Dark matter is a slippery substance. As far as we can tell, it must exist for our current models of the universe to work. But not only can’t we see it, feel it, or interact with it in any way, we’re not even sure what dark matter really is.

However, we do have some clues, such as how dark matter can interact or “talk” with ordinary matter through gravity. How this interaction occurs remains a mystery, but new work suggests that something called “non-minimal coupling” may be the solution.

“We asked ourselves: Is gravity wrong or are we just missing something important about the nature of dark matter?

What if dark matter and standard ‘baryonic’ matter interact differently than we always imagined?” explain the three authors, cosmologists Giovanni Gandolfi, Andrea Lapi and Stefano Liberati, in a press statement about their work.

“With our study, we tried to answer these intriguing questions.”

Our best guess for what dark matter might be is the cold, weakly interacting massive particles that experimental physicists around the world have been trying to detect for decades but have yet to find.

Despite how well this particular type of dark matter performs in our models, a few problems remain. One is called the “halo problem”, where the estimated density of dark matter in galaxies does not match what is known as an N-body simulation.

These models suggest that, in order to explain their current structure and motion, dark matter in low-matter galaxies must be “clustered” – meaning that it is most concentrated in the vicinity of the galaxy or beyond. But observations show that in most dwarf galaxies, dark matter is at the center.

This work is certainly not the first, and most likely not the last, to try to solve these dark matter problems, but the team has come up with a new tactic. The researchers suggest that if dark matter is not minimally related to gravity, then this solves the problem of cusps and another related problem called the radial acceleration ratio.

“In this paper, we propose another point of view for modifying the standard cold dark matter scheme to make it able to accurately describe the observed rotation curves of galaxies and at the same time faithfully reproduce the radial acceleration ratio,” the team writes in their new paper.

“The introduction of such a coupling could preserve the success of cold dark matter on large cosmological scales and at the same time improve its behavior in galactic systems.”

Non-minimal bonding is a bit of a misnomer. This means that dark matter is directly related to the curvature of spacetime, called the Einstein tensor. Simply put, this is a new type of interaction between dark matter and gravity. If there is a non-minimal connection, then dark matter interacts with space-time differently than ordinary matter.

“This feature of dark matter is not part of the new exotic fundamental physics,” the authors say.

“The existence of this non-minimal connection can only be explained with the help of known physics.”

This is just one of the hypotheses, and although it is in good agreement with the observational data that we have today, dark matter is still a complex beast. We’ll need a lot more research to determine if non-minimal coupling is really a feature of dark matter or just another hypothesis that pushes us to discover what’s really going on.

“The future of dark matter looks more rosy,” the authors note in a press statement.

“Further studies will be carried out to explore all the interesting implications of this proposed new feature of dark matter. We would not be surprised if we find that this non-minimal connection could solve other unanswered questions in the universe.”

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