WIMP

from Wikipedia, the free encyclopedia

WIMP ( Engl. W Eakly i nteracting m assive p articles "weakly interacting massive particles"; pun to wimp , wimp ') are hypothetical particles with a mass between a few tens to about a thousand GeV / c² (1 GeV / c² is little more than the mass of a neutron or proton). WIMPs have been postulated to solve the cosmological problem of dark matter in space .

The existence of dark matter is presumed because the gravity of the visible matter present in the universe would by far not be sufficient to explain the clumping of matter in the early phase of the cosmos, which led to the formation of galaxies . The majority of the matter contained in the universe must therefore consist of not directly visible ("dark") matter that participates in gravity. It is not yet clear what this should mean.

Dark matter could consist of heavy, electrically uncharged WIMPs that are only subject to weak interaction and gravity and cross space in large numbers. A WIMP would have a mass like two gold atoms and, like a neutrino, could fly through entire planets practically undisturbed. The English word “wimp” means “weakling” in German, which alludes to this inability to influence matter, and is also to be understood as a contrast to the MACHOs , which were also proposed as a hypothesis for dark matter.

Experiments

The experimental detection of WIMPs is the subject of current research . Because of the extremely rare interaction with any matter, attempts are made to detect WIMPs indirectly through their decays . In extremely rare cases, a WIMP has to collide directly with an atomic nucleus , which would thereby be converted into a radioactive nucleus. The detectors required for detection are, like neutrino detectors , mostly operated deep underground in order to avoid the background of radioactive background radiation and secondary cosmic radiation .

The most sensitive experiments at the moment use cryogenic detectors (detectors that operate at very low temperatures). This includes:

In 2007, DAMA delivered a result that was doubted by many: the experimenters claim to have observed a signal from WIMPs with a large detector made of sodium iodide (NaI). This result is difficult to reconcile with the results of the other experiments and the theoretical expectations.

Super WIMPs

An expanded concept provides for so-called super WIMPs, which are created by the disintegration of WIMPs. They have an even weaker interaction than WIMPs, since they are only subject to gravity.

The existence of super WIMPs would have an impact on the formation of galaxies. Super WIMPs would have moved very quickly in the early universe. Only after they came to rest could galaxies have formed. This would also have had less time to compress the matter in the center of the galaxies, which would also have had an effect on the density in the center of the dark matter halos . In this way it could possibly be shown whether these halos consist of WIMPs or Super-WIMPs.

Another possibility of detection could arise from the decay of WIMPs into Super-WIMPs themselves, since this could produce photons and electrons that would break up light atomic nuclei if they hit them. Evidence that the universe contains less lithium than expected could be explained by this.

Alternative Dark Matter Theories

Axions

Another particle that has been proposed to solve the dark matter problem is the axion . This also hypothetical particle could be produced in stars , among other things . By interaction with strong magnetic fields could be in a Photon transform , whose energy corresponds to the Axions. Axions from the sun were supposed to generate photons with frequencies in the range of X-rays . The CAST experiment at CERN deals with this particle with a 9 Tesla - magnets demonstrated.

MACHOs

Assumptions that dark matter is massive, but cold and non-radiating celestial bodies that are present in large numbers in galaxies ( MACHOs ), could not be confirmed by research.

Dark forces

According to Jonathan Feng from the University of California at Irvine and Jason Kumar from the University of Hawaii at Manoa , supersymmetry also allows alternative concepts without WIMPs, with several different types of particles. Many of these concepts also assume the existence of “dark forces”, hidden versions of the weak and electromagnetic force . The existence of dark electromagnetism would result in dark matter being able to emit and reflect hidden light. Even if such light and dark forces were hidden from us, they could still have an effect. Clouds of dark particles that penetrate each other would be distorted, which could also affect objects such as clusters of galaxies . Corresponding studies on the bullet cluster have shown that this effect can at least not be very strong. The dark forces, if they exist, are therefore only weak.

Another effect would result from the fact that dark forces would enable the particles of dark matter to exchange energy and momentum . Dark matter halos that would have been skewed initially would become spherical over time, which in turn would affect galaxies, especially dwarf galaxies . Dark matter in their environment moves particularly slowly. This causes particles to stay together longer. Small effects have more time to take effect. The observation that small galaxies are consistently rounder than large ones could be explained by this, which would be an indication of the existence of dark forces.

See also

Web links

Individual evidence

  1. ↑ a b Jonathan Feng, Mark Trodden: The hidden blueprint of the cosmos. In: Spectrum of Science , January 2011. Spectrum of Science Verlagsgesellschaft mbH, Heidelberg.