The LIGO/Virgo Collaboration sets new constraints on cosmic strings

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A large group of scientists from different institutes around the world has created the strongest constraints ever placed on cosmic strings using the Advanced LIGO/Virgo full O3 data. This dataset includes the most recent gravitational wave data from a network made up of three interferometers based in Italy and the United States.

Prof. Mairi Sakellariadou, a member of the LIGO/Virgo Collaboration, stated that "We wanted the most recent data from the third observing run [O3 dataset] to constrain cosmic strings."

According to field theories, the Universe expands as its temperature drops. This causes a series phase transitions that are followed by spontaneously broken synetries. These may leave behind topological defects or relics from the previous more symmetrical phase.

Sakellariadou stated, "Just to give an example, if water is in liquid form, and the temperature drops below zero degrees Celcius it will solidify." "Inside an Ice Cube, you can see filaments in the liquid water. This phenomenon could also occur in the Universe. One-dimensional topological defects, also known as cosmic strings, are sometimes referred to. Although particle physics models predict that cosmic strings exist, observational evidence is not available.

Sakellariadou stated that the gravitational effects of cosmic strings will be stronger the heavier they are. Analyzing observational data allows us to constrain the parameter that determines how heavy these objects, or the epoch for cosmic string formation.

Credit: LIGO-Virgo Collaboration

Researchers can also set constraints on cosmic strings to limit particle physics models, and other cosmological scenarios. Researchers can test particle physics models at energy levels that are not possible to reach with accelerators such as the Large Hadron Collider (CERN) using gravitational waves data.

Sakellariadou stated that constraints also depend on the model of cosmic strings used for string loop distribution. This is determined by involved numerical simulations.

Researchers have so far developed two numerical simulations. Bouchet and Lorenz, Ringeval, Sakellariadou and Sakellariadou first proposed it several years ago. The second one was developed by Blanco-Pillado and Olum.

Recent work by Steer, Ringeval and Sakellariadou on a new analytic loop model for string analysis interpolates the models from the past using numerical simulations. This model was used to constrain cosmic strings using gravitational waves data from the LIGO/Virgo/KAGRA collaboration.

The LIGO/Virgo/KAGRA Collaboration has placed constraints that are more stringent than those put forth by Big Bang nucleosynthesis or pulsar timer array. They also have improved upon previous LIGO/Virgo constraints by up to 2 orders.

"As we have more data, we can place even stronger constraints." Sakellariadou stated that it was important from a theoretical perspective to also build and explore new cosmic string models and study the implications of our work on particle physics beyond the Standard Model, as well as other cosmological scenarios.

The research was published by Physical Review Letters.

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R. Abbott et. al., Constraints On Cosmic Strings Using Information From The Third Advanced LIGOVirgo Observing Ran, Physical Review Letters (2021). Information for Journal: Physical Review Letters R. Abbott and al, Constraints On Cosmic Strings Using Third Advanced LIGOVirgo Observatory Run, (2021). DOI: 10.1103/PhysRevLett.126.241102

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