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Early Universe Modelling and Confrontation with Cosmological Data

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Is the Universe tied up with cosmic strings?

The very early stages of the Universe need be described with physics beyond the capacity of our current models. EU-funded physicists used field theory together with string theory to explore new inflation models and test them against observations.

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Inflation is a proposed period of accelerated expansion in the early Universe, where its size increased by a factor of a million billion billion over a period of a millionth of a billionth of billionth of a billionth of a second. This huge expansion is best explained by invoking a scalar field. As the field undergoes quantum fluctuations due to Heisenberg's uncertainty principle, anisotropies are produce in the cosmic microwave background that fills the Universe. The 'Early Universe modelling and confrontation with cosmological data' (EARLYUNIVERSE) project was launched to explore a new path. String theory appeared promising for solving the first stages of evolution. The 'theory of everything' unites all matter and forces in a single theoretical framework, in which the myriad of particles is replaced with a single building block. The strings are free to vibrate and different vibration modes were used to represent different particle types. EARLYUNIVERSE scientists used their string evolution model to quantify observable signals coming from cosmic strings. Cosmic strings are theoretical fault lines in the Universe, connecting different regions of space created in the moments after the Big Bang. Their power spectrum was computed with the greatest accuracy ever achieved from cosmic microwave background observations by the Planck spacecraft. The next step was to use observations of galaxy clusters to constrain cosmological model parameters. By coupling cosmological models based on scalar fields with changes to the cosmic microwave background, EARLYUNIVERSE opened new research directions. The results obtained so far have been described in seven scientific publications in leading international peer-reviewed journals. By further improving both the modelling formalism and the simulation code, the physicists hope to soon be able to investigate the inflation of the early Universe. The outcome will then be evaluated against the density distribution of the real Universe.

Keywords

Universe, cosmic strings, string theory, inflation models, early Universe, Universe modelling, cosmological data, string evolution model, cosmic microwave background, cosmological model

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