Cosmology and fundamental physics with the Euclid satellite (1206.1225v2)

Abstract: Euclid is a European Space Agency medium class mission selected for launch in 2019 within the Cosmic Vision 2015-2025 programme. The main goal of Euclid is to understand the origin of the accelerated expansion of the Universe. Euclid will explore the expansion history of the Universe and the evolution of cosmic structures by measuring shapes and redshifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid's Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

• The paper presents Euclid’s mission to map the large-scale structure of the Universe and test models of dark energy and modified gravity.
• It details advanced methodologies, including weak gravitational lensing and galaxy clustering, to measure cosmological parameters up to redshift 2.
• The study highlights how high-precision data can transform our understanding of dark matter, primordial fluctuations, and fundamental cosmological principles.

Summary of "Cosmology and Fundamental Physics with the Euclid Satellite"

Overview

The Euclid satellite, a medium-class mission by the European Space Agency, is designed to probe the accelerated expansion of the Universe by analyzing various cosmological parameters, with an emphasis on dark energy, dark matter, and gravitational physics beyond the standard models. This documentation is a review of Euclid’s Theory Working Group's scientific themes and the strategies intended to leverage Euclid’s capabilities to investigate fundamental physics questions.

Main Objectives

Euclid's primary mission is to understand the origin of the Universe's accelerated expansion by mapping the large-scale structure of the Universe out to a redshift of about 2 and measuring weak gravitational lensing and galaxy clustering over a large swath of the sky. This will enable precise determination of cosmological parameters and tests of gravitational theories.

Key Scientific Themes

1. Dark Energy and Modified Gravity: The core focus is to distinguish between models of dark energy and theories involving modifications to general relativity. Euclid aims to empirically test if the cosmic acceleration is due to a new energy component (dark energy) or a modification in gravity (modified gravity).
2. Dark Matter: Euclid will measure the distribution and properties of dark matter through gravitational lensing and galaxy cluster surveys to constrain models that involve massive neutrinos or light scalar fields potentially impacting dark matter behavior.
3. Initial Conditions and the Early Universe: By investigating the properties and evolution of initial density perturbations, Euclid aims to place constraints on the inflationary models that describe the very early Universe, offering insights into primordial fluctuations and subsequent structure formation.
4. Testing the Foundations of Cosmology: Fundamental assumptions such as the Copernican Principle, which posits a homogeneous and isotropic Universe on large scales, will be rigorously tested. Euclid will provide measurements needed to explore deviations from these assumptions due to local inhomogeneities or anisotropies.
5. Statistical Methods and Data Handling: Euclid’s mission will advance statistical measures and data analysis techniques essential for interpreting the vast data collected. This includes developing methods for mitigating systematic biases and understanding non-linear clustering effects.

Implications and Speculations

The mission will potentially revolutionize our understanding of fundamental physics by offering constraints on the nature of dark energy, testing modified gravity models, and providing a clearer picture of the early Universe. Euclid's high precision measurements of cosmic structures will be a cornerstone for theoretical advances and model validation in cosmology.

Conclusion

Euclid’s comprehensive data will deliver unprecedented insights into core cosmological parameters and the dynamics governing the Universe’s expansion and structure formation. By exploring the synergy between dark energy, modified gravity, and dark matter, Euclid is poised to be a pivotal mission that bridges observational data with theoretical physics, offering answers to long-standing questions and opening new lines of inquiry in the field. Future developments in cosmological and gravitational theories will likely pivot on the foundational data provided by the Euclid satellite's observations.