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Oscillons, Gravitational Wave Factories in Very Early Universe

A team of theoretical physicists at the University of Basel, Switzerland, has found that in the very early Universe, so-called oscillons — strong localized fluctuations of the inflaton field — can act as ‘gravitational wave factories.’

According to Antusch et al, oscillons produced a characteristic peak in the otherwise broad spectrum of gravitational waves. Image credit: University of Basel.

According to Antusch et al, oscillons produced a characteristic peak in the otherwise broad spectrum of gravitational waves. Image credit: University of Basel.

Although Albert Einstein had already predicted the existence of gravitational waves, their existence was not actually proven until fall 2015, when the Laser Interferometer Gravitational-wave Observatory (LIGO) observed the waves produced by the merger of two black holes.

Gravitational waves are different from all other known waves. As they travel through the Universe, they shrink and stretch the space-time continuum; in other words, they distort the geometry of space itself.

Although all accelerating masses emit gravitational waves, these can only be measured when the mass is extremely large, as is the case with black holes or supernovas.

However, gravitational waves not only provide information on major astrophysical events of this kind but also offer an insight into the formation of the Universe itself.

In order to learn more about this stage of the Universe, Professor Stefan Antusch and his colleagues from the Particles and Cosmology Group at the University of Basel’s Department of Physics are conducting research into what is known as the stochastic background of gravitational waves.

This background consists of gravitational waves from a large number of sources that overlap with one another, together yielding a broad spectrum of frequencies.

“Shortly after the Big Bang, the Universe we see today was still very small, dense, and hot. Picture something about the size of a football,” Prof. Antusch said.

“The whole Universe was compressed into this very small space, and it was extremely turbulent.”

“Modern cosmology assumes that at that time the Universe was dominated by a particle known as the inflaton and its associated field.”

The inflaton underwent intensive fluctuations, which had special properties.

They formed clumps, for example, causing them to oscillate in localized regions of space.

These regions are referred to as oscillons and can be imagined as standing waves.

“Although the oscillons have long since ceased to exist, the gravitational waves they emitted are omnipresent — and we can use them to look further into the past than ever before,” Prof. Antusch said.

Using numerical simulations, the physicists were able to calculate the shape of the signal of an oscillon.

It appears as a pronounced peak in the otherwise rather broad spectrum of gravitational waves.

“We would not have thought before our calculations that oscillons could produce such a strong signal at a specific frequency,” Prof. Antusch said.

“Now, in a second step, experimental physicists must actually prove the signal’s existence using detectors.”

The team’s results were published in the Jan. 6, 2017 issue of the journal Physical Review Letters.

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Stefan Antusch et al. 2017. Gravitational Waves from Oscillons after Inflation. Phys. Rev. Lett. 118 (1): 011303; doi: 10.1103/PhysRevLett.118.011303

This article is based on a press-release from the University of Basel.