The new model aims to explain the lack of miniature black holes in the early universe

Scientists from the Research Center for the Early Universe (RESCEU) and the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) at the University of Tokyo have applied the well-understood and highly validated quantum field theory, usually applied to the study of the very small, to a new goal , the early universe.

Their survey concluded that there should be far fewer miniature black holes than most models suggest, although observations to confirm this should soon be possible. The particular kind of black hole in question could be a contender for dark matter. Their work was published in Physical inspection letters and Physical overview D.

The study of space can be a daunting thing, so make sure we’re all on the same page. Although the details are unclear, there is general agreement among physicists that the universe is about 13.8 billion years old, began with a bang, expanded rapidly in a period called inflation, and somewhere along the line went from homogeneity to content containing detail and structure.

Most of the universe is empty, but despite this it appears to be considerably heavier than what we can see – we call this discrepancy dark matter, and no one knows what it might be, but evidence is mounting that it could be black holes, specifically the old ones.

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

“They are interesting for other reasons as well, since the recent innovation of gravitational wave astronomy has seen the discovery of binary black hole mergers, which can be explained by the fact that PBHs exist in large numbers. But despite these strong reasons for their expected number, we have not seen any directly and now we have a model that should explain why this is the case.”

Kristiano and his supervisor, Professor Jun’ichi Yokoyama, currently the Kavli Director of IPMU and RESCEU, extensively researched various models for the formation of the PBH, but found that the main contenders did not match actual observations of the Cosmic Microwave Background (CMB), which is something like a fingerprint remnant 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 it can only paint part of the picture at best.

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

“In the beginning, the universe was incredibly small, much smaller than the size of a single atom. Cosmic inflation quickly expanded this by 25 orders of magnitude. At that time, waves traveling through this small space could have relatively large amplitudes, but very We found that these small but powerful waves may translate into the otherwise unexplained amplification of much longer waves that we see in the current CMB,” said Yokoyama.

“We believe it’s because of occasional instances of coherence between these early short waves that can be explained using quantum field theory, the most robust theory we have to describe everyday phenomena like photons or electrons. Whereas 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 of something at one extreme scale seems to explain something at the opposite end of the scale.

If, as Kristiano and Yokoyama suggest, small-scale fluctuations in the early universe affect some of the larger-scale fluctuations we see in the CMB, this could change the standard explanation of the coarse structures in the universe. But since we can use CMB wavelength measurements to effectively constrain the range of corresponding wavelengths in the early universe, this will necessarily constrain any other phenomena that might rely on these shorter, stronger wavelengths. And here comes the PBH.

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

At the time of writing, the world’s gravitational wave observatories, LIGO in the US, Virgo in Italy and KAGRA in Japan, are in the middle of an observational mission to observe the first small black holes, likely PBHs. In any case, the results should offer the team solid evidence to help them further refine their theory.