Researchers at the University of Tokyo’s Research Center for the Early Universe and Kavli Institute for the Physics and Mathematics of the Universe have used quantum field theory to study the early universe. Their research suggests there should be fewer miniature black holes, or primordial black holes (PBH), than previously thought. These PBHs are considered a potential explanation for dark matter. The team, including graduate student Jason Kristiano and Professor Jun’ichi Yokoyama, found that existing models for PBH formation did not align with observations of the cosmic microwave background. Their findings could impact our understanding of the universe’s structure.
Quantum Field Theory and the Early Universe
Researchers at the Research Center for the Early Universe (RESCEU) and Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) at the University of Tokyo have applied quantum field theory, a well-established framework typically used to study the very small, to the early universe. This exploration led to the conclusion that there should be fewer miniature black holes, also known as primordial black holes (PBH), than most models suggest. These PBHs are considered by many researchers as a strong candidate for dark matter, an unexplained phenomenon that accounts for the universe’s unaccounted mass.
The team, led by graduate student Jason Kristiano and his supervisor, Professor Jun’ichi Yokoyama, director of Kavli IPMU and RESCEU, found that the leading models for PBH formation do not align with actual observations of the cosmic microwave background (CMB), a remnant radiation from the Big Bang. The team used a novel approach to correct the leading model of PBH formation from cosmic inflation so it better aligns with current observations and could be further verified with upcoming observations by terrestrial gravitational wave observatories around the world.
The Role of Small-Scale Fluctuations in the Early Universe
The researchers suggest that early small-scale fluctuations in the universe could affect some of the larger-scale fluctuations we see in the CMB. This could alter the standard explanation of coarse structures in the universe. Given that we can use measurements of wavelengths in the CMB to effectively constrain the extent of corresponding wavelengths in the early universe, it necessarily constrains any other phenomena that might rely on these shorter, stronger wavelengths. This is where the PBHs come back in.
“It is widely believed that the collapse of short but strong wavelengths in the early universe is what creates primordial black holes,” said Kristiano. “Our study suggests there should be far fewer PBHs than would be needed if they are indeed a strong candidate for dark matter or gravitational wave events.”
Observing Primordial Black Holes
At the time of writing, the world’s gravitational wave observatories, LIGO in the U.S., Virgo in Italy and KAGRA in Japan, are in the midst of an observation mission which aims to observe the first small black holes, likely PBHs. The results of this mission should offer the team solid evidence to help them refine their theory further.
Theoretical Implications and Future Research
The research conducted by Kristiano and Yokoyama has significant implications for our understanding of the early universe and the formation of primordial black holes. Their work suggests that quantum field theory, typically used to describe phenomena at the smallest scales, can be applied to explain phenomena at the largest scales, such as the structure of the universe and the formation of black holes.
The team’s findings also challenge the prevailing view that primordial black holes are a strong candidate for dark matter. If their theory is correct, there should be far fewer PBHs than would be needed if they are indeed a strong candidate for dark matter or gravitational wave events. This has significant implications for our understanding of the universe and opens up new avenues for future research.
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