Could The Cosmos Be A Collider?

The cosmos and elementary particles—the largest and smallest objects studied by physicists—are intricately linked.

AsianScientist (July 28, 2017) – Scientists from Hong Kong University of Science and Technology and Harvard University have discovered the relationship between the spectrum of elementary particles and the distribution of the contents of our observable universe. The research was published in the journal Physical Review Letters.

Our observable universe is the largest object that physicists study, spanning a diameter of almost 100 billion light years. The density correlations in our universe—correlations between the numbers of galaxies at different parts of the universe—indicate that our vast universe has originated from a stage of cosmic inflation.

On the other hand, elementary particles are the smallest object that physicists study. The standard model (SM) of particle physics was established 50 years ago, describing all known particles and their interactions. Despite this, little is known about the relationship between the density distributions of the vast universe and the nature of the smallest particles.

“Ongoing observations of cosmological microwave background and large scale structures have achieved impressive precision, from which valuable information about primordial density perturbations can be extracted,” said Assistant Professor Wang Yi of HKUST’s department of physics who co-authored the paper.

“A careful study of this SM background would be the prerequisite for using the cosmological collider to explore any new physics, and any observational signal that deviates from this background would then be a sign of physics beyond the SM.”

In this study, the team carried out a two-step task to define the background of the SM model. The first step was to measure the SM spectrum during inflation, which turned out to be dramatically different from that obtained from the particle physics calculation in flat space. The second step was to figure out how the SM fields fit into the cosmological density correlation functions.

“Just like the line pattern of the light you see when observing a mercury lamp through a spectrometer, the mass distribution of SM particles also presents a special pattern, or a ‘mass spectrum’ which can be viewed as the fingerprint of the SM,” explained Dr. Xianyu Zhong-Zhi, a co-author and physicist at the Center for Mathematical Sciences and Applications at Harvard University.

“However, this fingerprint is subject to change if we change the ambient conditions. Just like the light spectrum changes when we apply a strong magnetic field to the lamp, the spectrum of the SM particles at the time of inflation is very different from the spectrum of the SM particles now. This is due to the inflationary background,” Xianyu added.

The team carefully examined the effects arising from inflation and showed how the mass spectrum of SM would look like when different inflation models were applied. They found that the spectrum of elementary particles is encoded in the statistical distribution of the contents in our observable universe today.

Their findings mark the first step of cosmological collider phenomenology and pave the way for future discovery of new physics.

“In our minimal setup, the SM particles interact with the driving force of inflation rather weakly. But if some new particles can mediate stronger interactions between these two sectors, we would expect to observe a stronger signal of new physics,” said Wang. “The cosmological collider is an ideal arena for new physics beyond the SM.”

The article can be found at: Chen et al. (2017) Standard Model Background of the Cosmological Collider.


Source: Hong Kong University of Science and Technology; Photo: Pexels.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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