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Early Universe Modelling and Confrontation with Cosmological Data

Final Report Summary - EARLYUNIVERSE (Early Universe Modelling and Confrontation with Cosmological Data)

EARLYUNIVERSE: Early Universe Modelling and Confrontation with Cosmological Data

The aim of this research project was to study non-trivial interrelations between fundamental theory, phenomenology and cosmological observation, in order to obtain a more comprehensive picture of the physics of the early universe and to identify new promising directions for future research. The project was developed along three interrelated lines of work, hereafter workpackages (WPs):

WP1) Cosmological modelling in fundamental theory and searching for new phenomenological signals
WP2) Quantitative study of the phenomenology of existing models
WP3) Exploration of physical effects at different scales (high versus low energy) in the context of models of the early and late universe, thus linking high-energy physics to astrophysical observation

The above three WPs were designed so as to maximise overlap among their components. For example, we focused on inflationary models, cosmic string networks and axion fields, which can all simultaneously exist according to fundamental high-energy theory. This allows information from different approaches to be combined, thus helping to bridge the interdisciplinary gap between high-energy physics and cosmological/astrophysical observations.

The work performed since the beginning of the project includes the study of multi-field models and effective field theory approaches to cosmological inflation (WPs 1 & 2), the evolution of cosmic superstrings in warped spacetimes (WP1), effects of charges and currents on cosmic string networks (WP2), the computation of string powerspectra (WPs 2 & 3), the potential role of gravitational shocks on Gamma-ray bursts (WP3), and the possibility of constraining models with dark energy and/or axion fields using cosmic distance measures and the temperature-redshift evolution (WPs 3 & 2). Some notable results include:

• Efficient computation of cosmic string power-spectra, reducing computational times by factors of order 100, while at the same time improving numerical accuracy. This allows, for the first time, to perform Markov-Chain Monte-Carlo analysis for Inflation+String models.
• Development of a novel technique allowing us to use Sunyaev-Zel’dovich measurements of galaxy clusters to constrain cosmological models with scalar fields, including axions. This significantly enlarges the available observational toolbox for studying the early universe.
• Identification of a new theoretical bound on a large class of two-field inflationary models, by utilizing effective field theory techniques and non-adiabaticity effects. This can be used to rule out significant part of the previously allowed two-field models.

The results of this project have opened new promising research directions, which are currently being explored and will likely play an important role in the researcher’s on-going scientific work programme after the end of the Fellowship. In particular, the drastic improvement in the computation of string-power spectra has allowed (as mentioned above) the use of Markov-Chain Monte-Carlo techniques to run a comprehensive study of inflationary models with cosmic strings. We plan to use the software developed in this project to perform such a comprehensive study as part of the Planck satellite analysis pipeline for cosmic defects. The next important step is to then generalise and apply these techniques to the more interesting (but much more complex) case of cosmic superstrings. On the more observational side, the new method mentioned above (bullet point 2) allows the synthetic combination of Sunyaev-Zel’dovich measurements, cosmological distance determinations, and galaxy ageing techniques to constraint cosmological effects beyond the standard model. This includes effects of cosmic axions and evolving dark energy, and is already part of the Euclid satellite theory programme for testing fundamental physics (Amendola et al., arxiv:1206.1225) of which the researcher has become a member during this Fellowship.

Overall, the project has resulted in 7 scientific publications in leading international peer-reviewed journals, one publication currently under peer-review, and at least 5 more research papers to be submitted in peer-reviewed journals in the academic year 2013-2014. The work involved 24 collaborators (including 6 PhD students and 3 Master’s students) from several universities and research institutes in 8 EU countries (UK, Portugal, Spain, Poland, Italy, France, Switzerland, Netherlands) and the US. Results were presented through scientific talks and seminars in national and international conferences (in the UK, Greece and China) as well as visits to other universities (in the UK and Spain). In addition, the researcher gave a 6-hour and a 10-hour graduate course at Koc University, Turkey and at the host institution respectively. A more specialised 4-hour course was given in Bilbao, Spain. This project also contributed to outreach activities in both Spain (through the organisation of an intensive 2-week summer course in Cosmology for talented nationally selected high-school students) and Greece (through a newspaper supplement article on the researcher’s work in Early Universe Cosmology).