Whilst it is evidenced by many cosmological and astrophysical observations, dark matter still evades detection on Earth. As a consequence, the current particle and astroparticle literature is quite rich in proposals trying to satisfy cosmology with dark matter, and explaining its non-finding.
[image credits: 36Janusz (Pixabay)]
Whilst I promised @agmoore2 to write about some non-dark topic this week, I changed my mind… I could not resist after having read an interesting scientific article discussing mirror worlds and mirror dark matter.
In the world as we know it, elementary particles and the way they interact are governed by the Standard Model of particle physics. This yields a quite accurate description of nature.
However, the Standard Model does not contain any particle that could be dark matter.
Towards a hidden mirror world
Many theories featuring dark matter rely on the existence of a hidden world.
This hidden world is made of new elementary particles that do not feel three of the four fundamental interactions: electromagnetism, weak and strong interactions. Instead, they are sensitive to new interactions specific to the hidden world.
[image credits: Alexas_Fotos (Pixabay)]
In the mirror-world construction, we push this idea further.
We associated to the elementary particles of the Standard Model (quarks, electrons, positrons, the Higgs boson, etc.) mirror counterparts (mirror quarks, mirror electrons, mirror positrons, a mirror Higgs boson, etc.).
As a second step, we take the three fundamental interactions of the Standard Model (electromagnetism, the weak interactions and the strong interactions) and define a similar dynamics in the mirror world (mirror electromagnetism, mirror weak interactions and mirror strong interactions).
In a few words, we make an entire, secluded, mirror copy of the Standard Model. Whilst the visible world is sensitive to the usual fundamental interactions, the mirror world is solely governed by the mirror interactions.
On different lines, the mirror elementary particles could combine to form mirror neutrons, mirror protons and even mirror atomic nuclei (similarly to what happens in the visible sector). In the mirror-world framework, this mirror matter is dark matter.
Crossing the mirror
Particle physics models are based on principles of symmetries, which implies that at the level of the theoretical modelling, anything allowed by the symmetries has to be included. Going back to the mirror-world framework, all underlying symmetries permit the existence of connections between the visible and mirror worlds.
Experimental constraints however indicate that these connections have to be extremely fainted. Consequently, mirror particles can interact with normal matter, but only very occasionally.
In other words, mirror dark matter passing through Earth can interact with matter once in a while, which could potentially be recorded.
In the discussed scientific article, the authors predict the hints that mirror dark matter should leave in a dark matter detection experiment named LUX. The LUX detector contains 370kg of liquid Xenon surrounded by state-of-the-art electronics, and is extremely sensitive to the tracks left by a dark matter particle hitting one of the Xenon nuclei of the detector.
The results are given in the figure below.
[image credits: arxiv]
The two axes represent quantities that can be measured by LUX, and the dots consist in data.
Whilst LUX is shielded to prevent visible particles from interacting in the detector, this sometimes happens. The corresponding background expectation consists in the cloud of points shown on the figure. There is indeed no dark signal!
In contrast, hints for the existence of a mirror world would manifest as an extra concentration of points within the contours bounded by the solid lines. The results do not feature this signal.
In this post, I described a particle physics construction in which the Standard Model (or the visible world) comes accompanied with a secluded mirror copy to which it is feebly linked. This mirror world consists in dark matter.
This weak connection between the visible and mirror worlds allows for the detection of the mirror world in standard dark matter experiments. I have detailed a recent article in which the absence of any mirror world signal has been highlighted.
If a mirror world exist, its connection to our world has to be even weaker than expected!
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