EARLYUNIVERSE

Early Universe Modelling and Confrontation with Cosmological Data

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 Obiettivo del progetto (Objective)

'In this exploratory project we will study the non-trivial interrelations between fundamental theory, phenomenology and observation in cosmology, in order to obtain a comprehensive picture of the physics of the early universe, and to identify new promising directions for future research. The project will develop along three interrelated lines of work. First, we will seek new possibilities for cosmological model building in string theory and explore the range of phenomenological features that theory allows. One focal point will be our model of Wilson line inflation, which offers a new path for understanding inflation in heterotic theory - an open problem - and which presents rich phenomenology, including non-Gaussianity and gravitational waves. This connects to our second line of work, which is a quantitative study of the phenomenological features of new and existing models. We will focus on hybrid 2-field models that are both well-motivated and phenomenologically rich, producing isocurvature modes, non-Gaussianity and cosmic strings. We will study these features quantitatively and use our state of the art string evolution model to quantify observational signals coming from cosmic strings. Third, we will explore non-trivial relations between high-energy physics sectors that do not play a dominant role in the early universe, but are part of the same underlying theory and can produce observable signals in the late universe. We will use high quality data in innovative ways to constrain high-energy parameters in the underlying fundamental theory. We shall give special attention to axions (e.g. from type IIB string theory used to build the 2-field models mentioned above) and their coupling to photons, fermions and gravitons. This is an interdisciplinary project combining information from theory, phenomenology and observation to maximize impact. There are many connections between the different lines of work and unexplored areas where new promising directions could be found.'

Introduzione (Teaser)

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.

Descrizione progetto (Article)

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.