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Nassim Bozorgnia, Joseph Bramante, James M. Cline | Canadian Journal of Physics | (2024)
Primary Link DOI Openalex Full text (OA)

Key Takeaways

Sample Definition And Size

This is a review article summarizing theoretical proposals and experimental searches for dark matter; it is not based on a primary study with a defined sample size, but rather synthesizes existing literature and initiatives, notably the 2020 Astroparticle Community Planning Green Paper by the Canadian Subatomic Physics community, updated with recent advances.

Study Type

Review article (theoretical and experimental review), based on a Green Paper and updated to reflect recent developments in dark matter research.

Conflicts Of Interest

No conflicts of interest are declared in the abstract or metadata available.

Results Summary

The paper provides an overview of leading theoretical dark matter candidates and describes how these proposals have motivated a broad global search program, including direct laboratory searches and astrophysical observations; no specific quantitative results, statistics, p-values, or effect sizes are reported in the abstract.

Abstract

Astrophysical observations suggest that most of the matter in the cosmos consists of a new form that has not been observed on Earth. The nature and origin of this mysterious dark matter are among the most pressing questions in fundamental science. In this review, we summarize the current state of dark matter research from two perspectives. First, we provide an overview of the leading theoretical proposals for dark matter. And second, we describe how these proposals have driven a broad and diverse global search program for dark matter involving direct laboratory searches and astrophysical observations. This review is based on a Green Paper on dark matter prepared as part of the 2020 Astroparticle Community Planning initiative undertaken by the Canadian Subatomic Physics community but has been significantly updated to reflect recent advances.

Referenced In

StarTalk

Season 17, Episode 16: Dark Matter Candidates Explained

Hey StarTalkers! Season 17, episode 16 had Neil and Chuck discussed the “dark” universe with Professor Katherine Freese.

A fan question called on Professor Freese to run-through the leading candidates for the unknown source of gravity known as dark matter:

Dark Universe Decoded with Katherine Freese - StarTalk Radio

(from 33:30)

She names three key candidates: WIMPs, axions and primordial black holes. But what are they? And why do we think they could make up dark matter?

WIMPs

These Weakly-Interacting Massive Particles are probably the most well-known dark matter candidate.

The “weakly-interacting” part isn’t an insult. They literally interact with ordinary matter through the weak force. A 2024 paper explains that in the energetic, early universe, weakly-interacting particles were created thermally and frequently interacted with normal matter.

But as the universe expanded and cooled, the interactions stopped and left behind a “relic” of now basically inert particles. This relic would be pretty close to the amount of dark matter we see today.

Many particles could be WIMPs, including neutrinos, supersymmetric particles (like the neutralino) and the inert Higgs doublet. Beyond the fact that some dark matter is probably neutrinos, we aren’t too sure.

Axions

Understanding axions fully would require a whole post, but the basics are easy enough to get. In order to solve an outstanding problem in particle physics, two physicists proposed a new symmetry, which can be spontaneously broken. Just as the Higgs Boson is the particle associated with the breaking of electroweak symmetry, the axion is the particle associated with the breaking of this symmetry.

The major issue with this is that axions barely have mass, so we’d need a lot of them to account for dark matter.

Primordial Black Holes

In the early universe, it may have been possible for much lighter black holes to form than today. One with the mass of Earth, for instance, would be about the size of an American dime. These tiny, primordial black holes could be zipping around the universe today and make up a substantial portion of dark matter.

There are limitations on their size – Hawking radiation would have “evaporated” tiny ones already, for instance – but LIGO’s detection of gravitational waves from merging black holes has reignited interest.

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