DEMO

The dark sector in cosmology and impact on present and future generation experiments

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 Obiettivo del progetto (Objective)

'Cosmology has seen the growth of an enthusiastic interest in the Dark Universe we live in. Observations show that ordinary matter is only a small fraction of the total energy in the Universe. The rest is in the form of Dark Matter and Dark Energy. They both emit no light: Dark Matter feels gravitational attraction and allows galaxies to form; Dark Energy contrasts gravity and makes the Universe expand faster and faster. My research project will identify the observable effects that indicate dynamics in the Dark Energy component, disentangling it from a cosmological constant. To do this I will investigate interactions among Dark Energy and other species in the Universe. Furthermore, I will consider the case in which General Relativity itself is modified. I will predict effects on cosmic microwave background and structure formation. Halo profiles, supercluster structures, the Integrated Sachs-Wolfe effect are some of the features affected by an interaction that can make Dark Energy dynamics observable. I will compare my findings to experiments like PLANCK and EUCLID. The PLANCK satellite is now observing the cosmic microwave background with precision higher than ever. As part of the PLANCK collaboration, I can analyze the data and extract from them information on cosmology and Dark Energy. EUCLID has reached the final selection stages of the ESA Cosmic Vision Program: its proposal is based on a satellite which will observe galaxies at distances higher than ever. I will forecast the ability of EUCLID to investigate Dark Energy and modified gravity through effects on structure formation. The research in Geneva will allow me to investigate the impact of the Large Hadron Collider findings right at the time when LHC results will be made available. The discovery of an interaction would be inestimable for cosmology, providing a specific tool to disentangle dynamical dark energy from a cosmological constant, with a profound impact on our knowledge of the universe.'

Introduzione (Teaser)

An EU-funded project reviewed alternative models to dark energy without the need to invoke a cosmological constant. Showing that dark energy is a dynamical contribution should dramatically increase our knowledge of the Universe.

Descrizione progetto (Article)

In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the Universe. The cosmological constant is the simplest possible form of dark energy, leading to the current standard model of cosmology.

The EU-funded project 'The dark sector in cosmology and impact on present and future generation experiments' (DEMO) sought to disentangle dark energy from the cosmological constant by identifying dynamical interactions with other forms of matter. The observable Universe contains only a small fraction of ordinary matter, with the rest being dark energy and dark matter.

Scientists explored the possibility that dark energy is dynamical and that gravitational force between dark matter particles is different compared to the general theory of relativity. This was the case of coupled dark energy models, in which dark matter particles feel the presence of a fifth force that is larger than gravity.

Based on this, DEMO implemented a numerical code that allowed test coupling between dark energy and dark matter. Small differences in the Hubble expansion parameter calculations and small fluctuations in the baryonic matter density led scientists to conclude that a non-zero coupling is compatible with data. These cosmological data were produced by the Planck Collaboration in 2013.

Scientists showed for the first time that the amount of dark energy at early stages depends on the epoch at which dark energy started to become relevant. While there are tight constraints regarding the dark energy presence since photon and neutrino decoupling, larger amounts of dark energy are allowed at later times.

DEMO work resulted in formulating a scenario in which dark energy and dark matter are two aspects of the same fluid.

Project work regarding dark energy, dark matter and their comparison to data was published in 12 papers in international journals. Amongst these, there are also works on theoretical models and their comparison to data.