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There is something that does not fit. Stars, planets and gases do not have enough mass to explain why they are held in place in galaxies of gravity. Galaxies are spinning too fast, stars should spin in all directions. There is something that makes galaxies heavier than they look and that Something called black matter.
About 83% of the mass of the universe is a mystery.
Over the last thirty years, scientists have seen no dark matter twinkling through experiments designed to reveal the most popular candidates.
"There is a keen sense of" crisis "in the dark matter field, which stems from the lack of evidence of the most popular dark matter candidates, despite the enormous efforts to recover these particles, says Gianfranco. Bertone, a colleague in an article in the journal Nature entitled "A new era in dark matter research." This briefly describes what we have found so far and where researchers will look further.
– But I would say that's a good thing. For the moment, new opportunities will be announced. Personally, I am optimistic that we will learn a lot more about dark matter over the next decade, "Bertone told Nature's podcast.
The beautiful WIMPs
The most promising explanation of what dark matter is for something has been said massive particles weakly interacting or WIMP. They are hypothetical particles that have a mass and thus affect gravity, but otherwise they perish only through the common material.
Are Raklev (Photo: UiO).
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The continuation of the WIMP took place in the CERN Particle Crash LHC and in the large underground xenon detector (LUX) located at the bottom of a South Dakota mine.
Are Raklev, professor at the University of Oslo and expert in astroparticle physics, explains why the WIMP is such a popular candidate for explaining dark matter.
"Everything is a matter of magic numbers, if there is a particle that only has what we call electrolytic interactions with the world, a so-called weak particlethen it will automatically be the right amount to explain the dark matter. It's something that has been called the WIMP miracle.
But the hunt has not advanced yet.
– Is it time to put a line on this assumption?
– It is almost impossible to completely exclude the possibility of finding a WIMP particle. But as you search for it with more and more sensitive experiences, there is less space left for that. He must then have a very special behavior to escape all the experimental tests that try to find him, "Raklev told research.no.
He explains that it is the wish that physics be beautiful or "natural".
"As a boy, faith ends up losing faith, because the patterns you need to use become so complex and so special, it should preferably feel natural and elegant.When we learn more and more after WIMP and we do not find it, it becomes less and less elegant and more special.
Personally, Raklev has not lost confidence in the WIMP and thinks he should be 5 to 10 years old.
The figure presents five main ideas about the nature of dark matter, as well as other ideas with a similar starting point. (Illustration: Used with the permission of Nature: Nature, "A new era in the search for dark matter", Gianfranco Bertone and Tim M. P. Tait. [COPYRIGHT] October 2018.)
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An explosive theory
But that people are walking and knowing a "climate of crisis", Raklev will not participate.
– No, it's a difficult word to use. It is more the fact that the search for other explanations of dark matter has become a natural transition.
And there is no need for ideas to explore. Previously, Raklev worked with an alternative candidate called gravitino. This is the unknown partner of graviton thought particle. A graviton is the particle that is believed to be able to transmit to gravity, just as the photon, the luminous particle, transmits electromagnetic power.
– We have never seen Gravitonet. I had a boyfriend once as aware that the only thing I was working with was hypothetical partners for hypothetical particles.
The craziest hypothesis that Raklev knows comes from the Danish theorist Holger Bech Nielsen. He believes he can explain the extreme explosion of Tunguska in Siberia in 1908, according to which there was a mass of dark matter composed of 12 main earthquakes that crossed nature and destroyed the mileage traveled by forests.
After crazy theories, it is also suggested that dark matter can create its own "molecules" and form a dark shadow universe with planets and stars in the middle of the universe in which we live. Or maybe dark matter is stuck in a fifth dimension as in Kaluza-Klein particle theory.
Black hole restored as an explanation
"If we go back to slightly more central assumptions, does anyone look like a new first candidate?
– Not very clear. Axions is one of the favorites, so we have sterile neutrinos. Now you've also moved black holes as a candidate, even though you've been pretty sure for a long time that there are no black holes, "says Raklev.
The detection of gravity waves is the reason for renewed interest in black holes as an explanation for dark matter. If the explanation of lack of mass in the universe is a plethora of black holes, we may not need hypothetical particles.
– The discovery of gravitational waves suggests that there are many more black holes of a particular type, called holes of the ur, that we thought.
– But there are some problems with the theory. First of all, it is problematic to imagine how all these black holes would be created in the primitive universe. We know basically what would make urure holes: there is in the fabric of the ancient universe small seals that attract more and more tissue by gravity and end up clinging to a black hole. We just do not understand how it will be enough to explain all the dark matter.
– It is also hard to imagine that we have already avoided discovering a huge collection of gigantic black holes. We looked for them.
Raklev therefore believes that this hypothesis will not lead.
Hunting Axions Using Mirrored Walls
In fact, the researchers found a type of dark matter particle. These correspond to the term because they do not reflect or absorb light, they do not interact with other matters and generate billions of them all the time. These tips are called neutrinos.
"It's good of a dark matter particle, but it's not the dark matter we're looking for," Raklev says.
They are not heavy enough to compensate for all the missing masses, not far away. But researchers have an idea that the particle could have a heavier brother, a sterile neutrino. These even rarely affect other topics, in fact so rare that it would take the whole life of the universe for one of them to come in between them. in an atom. It seems hopeless. But they can fall into something we can see, photons.
It is with the help of photons that you hope to discover the candidate axion of dark matter.
"There are quite new experiments in which researchers are trying to find axions, which are called" experiments through the wall ".
They are due to the fact that many photons are reflected between two reflecting mirrors in a strong magnetic field. Then, if a photo seems to appear at the back of the walls of the mirror.
– The photons must not be able to cross the walls. If this happens, they must have become an axion for a moment because they can pass.
The heavier siblings of the parties
The quest for dark matter is linked to the desire to find a theory of everything. In the 1970s, electromagnetism was linked to the weak and strong base power of the standard model. But physicists have not yet managed to reconcile the fourth natural force, gravity, with the other three.
The theory of supersymmetry can help solve this problem while explaining dark matter.
– Supersymmetry is an idea that there is an additional set of elementary particles heavier than those we know, called superpartners.
The researchers have been trying to detect signs of supersymmetry in the LHC particle accelerator, but nothing indicates that there are such ghost particles. Where is it?
Raklev says he and his colleagues performed a meta-analysis of the LHC data.
"What we have done is to look for a lot of research on supersymmetry and, when we process all the data and process the data statistically and correctly, there is a fairly large surplus of collisions at the LHC when strange events occur.
This strange thing is that there is an imbalance in some collisions.
– You see that you made a fabric and that substance goes in one direction, but in the other direction, there is no recoil. You can then conclude that you must have produced something invisible.
Raklev and the others are now waiting for the rest of the LHC data taken in the past year to be analyzed. Could there be a sensation around the corner?
– It will not appear until the month of March, so we can not say anything before, but it will be exciting.
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