The superstring theory tested in a cluster of galaxies

Several of the solutions of the theory of superstrings which can perhaps unify the particles of physics contain similar particles which one collects in the class known as axions. In some cases, these particles can modify the X-ray normally expected in clusters of galaxies. We thus posed new constraints on the theory of superstrings and axions.

Almost 50 years were necessary to discover the boson of Brout-Englert-Higgs and we expected to discover the particles of black matter so far essential in cosmology to give birth to galaxies before 2010. This is not the case at the moment and the two classes of particles most often postulated to account for dark matter, namely supersymmetric particles and axions are still being researched in terrestrial laboratories. But not only.

Indeed, the cosmos itself is a huge laboratory for the field of astroparticles and he conducted the most powerful experiment in over 13.7 billion years physical high energies, namely the big Bang himself. Today, a group ofastrophysicists recently reported via an article published in The Astrophysical Journal and available on arXiv that they had tried to highlight the presence of axions in a famous cluster of galaxies, Abell 426, better known ascluster of perseus which, as its name suggests, is located in the constellation from Perseus to around 250 millionlight years of the Milky Way.

Abell 426 is the brightest cluster of galaxies in the field of X-rays and for this reason it has been the subject of numerous studies using the satellite Chandra. X-ray comes from theprogram thermal plasma which is concentrated in the center of the cluster near which we find the radiogalaxy NGC 1275 (Caldwell 24), a lenticular galaxy giant which is also an active galaxy of type Seyfert 2. It therefore contains a supermassive black hole.

We know that there are magnetic fields in clusters of galaxies and it turns out that this is very interesting when we know the properties of several theories describing models of axions. The first come, as we will explain later, from a simple extension of the famous Standard model of particle physics. But particles which behave like the axions of this model are also often present in the solutions of superstring theory, which could describe all the forces and all the forms of matter ofUniverse observable.

Galactic clusters, factories with axions?

Particle astrophysicists have therefore come to understand that the intense X-ray radiation from the Perseus cluster combined with the presence of magnetic fields could perhaps make it possible to highlight the nature of at least part of its content in dark matter (it may be made up of particles of different natures but still falling under physics beyond the Standard Model) and more precisely to set bounds on the models of axions of the string theory. Here's how.

It turns out that all of these models predict that photons immersed in a magnetic field can be converted into axions, scalar bosons like that of Brout-Englert-Higgs, with a probability which depends on the coupling between the field of axions and the electromagnetic field. It's a bit like having a rubbing effect between two solid, the higher the coefficient of friction between the two solids, the more their movement will dissipate from the heat.

To look for signs of the conversion of X photons into axions, the researchers analyzed the observations extending over five days, made by Chandra, concerning the X radiation coming from the matter falling towards the supermassive black hole of NGC 1275. This radiation has a spectrum known but if the conversion process exists, this spectrum will be degraded in a very specific way.

No trace of the distortion of the spectrum was finally found but this does not mean that axions of the theory of superstrings are not present, only that some of the values ​​of the parameters describing these particles are excluded. So it is now with most models of axion particles in the range of mass below about one millionth of a billionth of a mass electron. The constraints have also become 100 times more precise compared to those obtained in experiments on Earth, like Cast at Cern. The probabilities of converting photons to axions may also be lower than previously imagined.

Everything, everything, everything you will know all about the axions

For those who would like to know a little more about the axions, here is some additional information already covered in ABSMARTHEALTH articles dedicated to hunting these hypothetical particles. Let us first explain how and why we postulated them.

The Standard Model of elementary particles predicts a very low value of the electric dipole moment of the electron, so small that it is not yet within the reach of experiments intended to measure it. Some theories beyond the standard model, on the other hand, predict a higher value, and this is why the quest for the measurement of the electric dipole moment of the electron is a possible research avenue for discovering new physics. Conversely, the standard model, more precisely the equations of the QCD, the theory of strong nuclear forces, authorizes a very high value for the dipolar moment of neutron, in contradiction with experiences which attribute none to him. To explain this result, we first assumed that one of the quarks of the standard model had a mass nothing. But here too, experiments have excluded this possibility. The most commonly accepted explanation today again involves new physics.

In 1977, Roberto Peccei and Helen Quinn hypothesized that the term in the equations of the standard model, responsible for the appearance of a dipole moment for the neutron, was made null by the existence of a new scalar field. . This term was also responsible for phenomena violating the CP symmetry in the context of the quantum chromodynamics which, there too, were not observed experimentally. As these two false predictions of the standard model "tainted" this one, the Nobel Prize in physics Frank Wilczek gave the name of the axion to the particle associated with the scalar field of Peccei and Quinn, with reference to a brand of detergent.

The Primakoff Axion and Effect

Over the years, interest in this new particle only increased when we realized that it was one of the best candidates for the title of particle. black matter. Indeed, the axion is a neutral particle, not very massive and which interacts very little with the matter. We tried to detect it on Earth using what is called the Primakoff effect, originally discovered with another particle of a scalar field, the pion. Applied to the axion, the Primakoff effect implies that when a magnetic field is strong enough, enough energetic photons can be converted into axions and vice versa. An idea proposed to produce and detect them was therefore to send a ray laser in an area with a strong magnetic field just in front of a Wall. Part of the photons would then change to axions which, due to their weak coupling with the material, will cross the wall without any problem to penetrate immediately afterwards in a second region having, also, an intense magnetic field. A reverse conversion process would occur, and the laser would therefore light an area behind the wall!

But so far none of the experiments carried out on Earth on this principle have revealed the existence of axions.

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