Cosmic belts can solve the problem of excess positrons in regions of the universe

A network of "cosmic strings: crisscrossing the universe may be responsible for the mysterious abundance of antimatter particles that intrigues scientists * Collapse defects in the structure of the universe may create an excess of antimatter or the return of a theory that dimmed with the discovery of the inflationary universe in the XNUMXs

Cosmic strings may play a role in the formation of galaxies. Theoretical astrophysicists at NASA have long predicted the existence of cosmic strings, thinner than an atom but stretching for long distances in the universe. They believe that they were created in an event known as "phase transitions" - dramatic changes in the structure of matter that occurred when the universe cooled shortly after the big bang. These strings have a new gravitational field and may have helped collect the material that formed the first galaxies.

The idea lost its luster when observations proved, at least as it seemed at the time, that these strings alone could not be responsible for the formation of galaxies. Instead, the "inflation" theory was developed to explain how the universe went through periods of exponential expansion early in its life, multiplying every little ripple in its structure, which has now become the nucleus of the first galaxies.

Now, however, theoretical astrophysicist Tanmay Vachaspati at Case Western Stern University in Ohio, suggests that space may be networked with a network of much lighter strings - too light to be directly responsible for the formation of galaxies, which may have been created during phase changes in the dark matter hidden in the universe.

Dark matter is a substance that does not emit any light and therefore cannot be observed directly, however by monitoring the effect of its gravity on the stars and galaxies, the astronomers calculated that it makes up about 85% of the matter in the universe.

Vachaspati believes that the beads themselves are made of antimatter and can solve cosmic mysteries. In 2008, physicists used the PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) satellite and reported that there is an unexplained excess of positrons - the antimatter twins of electrons. Some scientists have suggested that the excess positrons may have been created as debris from collisions between dark matter particles, but subsequent observations have failed to confirm the idea. This is where Vachaspati's string chain description comes into play. If the dark matter interacts very loosely with the known particles, as a result of the prediction of the leading models, then it is likely that the strings are composed of it.” says theoretical astrophysicist Alex Vilenkin at Tufts University in Massachusetts.

Over time, loops of these strings will contract and disappear, evaporating their energy by colliding with particles of matter. According to Vachaspati's calculations, collapsing loops of the light material in the strings would produce the excess positrons observed by Pamela.

Mark Pearce, a particle physicist at the Royal Institute of Technology in Stockholm and a member of the Pamela team, said it was difficult to evaluate Vachaspati's model without going into more detailed predictions about the positrons — such as their energy range — to compare the prediction with Pamela's observations. "It will also be necessary to examine whether the predictions of a flux of other cosmic particles, such as antiprotons, fit the existing data." added

Additional evidence for the existence of the cosmic strings can be discovered in experiments on Earth. If Vachaspati's theory is correct, loops in these strings should also find their way to the Milky Way and occasionally collide with Earth as well. "The oceans and ice caps are compressed enough for a loop to quickly lose its energy when it collides, which would produce gamma rays or other radiation," Vachaspati believes. He suggests that the radiation will be detected in an experiment designed to capture the flashes of light from passing neutrinos such as IceCube located under the South Pole and Antares in the Mediterranean. It may be possible to produce these dark strings in particle accelerators, he adds.

Another group of theoretical physicists claim to have discovered evidence of the cosmic strings from data from NASA's WMAP satellite, which maps temperature changes in the cosmic background radiation over about eight years. The group includes Mark Hindmarsh, a particle physicist at the University of Sussex in the UK, who said that Vachaspati's and his team's results are part of a more disruptive revival of the cosmic string theory.

"People today are more willing to play with the idea of ​​the cosmic strings than before" he said. "He attributes this trend to the growing understanding that the cosmic strings do not compete with the theory of inflation, but complement it. He also commented that greater availability of computing power is required to refine the calculations in cosmic string theory.

Vilenkin adds that astrophysicists are now paying more attention to strings because they can provide clear predictions about their effects on gravitational waves and the creation of energetic particles. "Observational techniques have become precise enough either to locate the strings or to impose constraints on the particle theories that predict them," he said.

For the article in Nature (subscription required)