New model aims to explain absence of miniature black holes in early universe

Researchers from the Research Center for the Early Universe (RESCEU) and the Kavli Institute for Physics and Mathematics of the Universe (Kavli IPMU, WPI) at the University of Tokyo have applied quantum field theory well understood and highly verified, generally applied to the study of the very small, towards a new target, the primitive universe.

Their exploration led to the conclusion that there should be far fewer miniature black holes than most models suggest, although observations to confirm this should soon be possible. The specific type of black hole in question could be a contender for dark matter. Their work was published in Physical Examination Letters And Physical examination D.

Studying the universe can be a daunting task, so let’s make sure we’re all on the same page. Although the details are fuzzy, the general consensus among physicists is that the universe is about 13.8 billion years old, started out with a bang, expanded rapidly during a period called inflation, and, at a at any given moment, has gone from homogeneous to containing detail and structure.

Most of the universe is empty, but even so, it appears to be much heavier than we can explain – we call this gap dark matter, and no one knows what it might be, but the evidence is mounting that this could be the case. be black holes, especially old ones.

“We call them primordial black holes (PBHs), and many researchers think they are good candidates for dark matter, but there would have to be a lot of them to satisfy this theory,” said student Jason Kristiano diploma.

“They are also interesting for other reasons, because since the recent innovation of gravitational wave astronomy, binary black hole mergers have been discovered, which can be explained if PBHs exist in large numbers. But Despite these strong reasons for their expected abundance, we have not seen any directly, and we now have a model that should explain why this is the case.”

Kristiano and his supervisor, Professor Jun’ichi Yokoyama, currently director of Kavli IPMU and RESCEU, have explored the various models of PBH formation extensively, but found that the main competitors do not match actual observations of the cosmic microwave background (CMB). , which is something of a leftover fingerprint from the Big Bang explosion marking the beginning of the universe. And if something doesn’t agree with solid observations, it either can’t be true or can, at best, only tell part of the picture.

In this case, the team used a new approach to correct the main model of PBH formation from cosmic inflation so that it better aligns with current observations and can be further verified with future observations. terrestrial gravitational wave observatories around the world.

“At the beginning, the universe was incredibly small, much smaller than the size of a single atom. Cosmic inflation quickly increased this figure by 25 orders of magnitude. At that time, waves passing through this tiny space could have have relatively large amplitudes, but very “We found that these tiny but strong waves can result in an otherwise inexplicable amplification of much longer waves that we observe in the current CMB,” Yokoyama said.

“We believe this is due to occasional instances of coherence between these early short waves, which can be explained using quantum field theory, the most robust theory we have for describing everyday phenomena such as photons or electrons While individual short waves would be relatively powerless, coherent groups would have the power to reshape waves much larger than themselves. This is a rare case where a theory has something to do. an extreme scale seems to explain something at the opposite end of the scale.”

If, as Kristiano and Yokoyama suggest, the universe’s early small-scale fluctuations affect some of the larger-scale fluctuations we observe in the CMB, this could change the standard explanation of the universe’s gross structures. But also, given that we can use the wavelength measurements in the CMB to effectively constrain the extent of corresponding wavelengths in the early universe, this necessarily constrains any other phenomena that might rely on these shorter and stronger wavelengths. And that’s where PBHs come into play.

“It is widely believed that the collapse of short but strong wavelengths in the early universe caused the creation of primordial black holes,” Kristiano said. “Our study suggests that there should be far fewer PBHs than would be necessary if they are indeed good candidates for dark matter or gravitational wave events.”

At the time of writing this article, the global gravitational wave observatories, LIGO in the United States, Virgo in Italy and KAGRA in Japan, are in the midst of an observation mission which aims to observe the first small black holes, probably PBH. Either way, the results should provide the team with solid evidence to help them further refine their theory.