ERC FUNDED PROJECTS

The average spectrum of the cosmic microwave background (CMB) has long been known to be extremely close to a perfect blackbody. Yet, several processes, standard and non-standard, exist that may cause deviations from a blackbody spectrum, commonly referred to as CMB spectral distortions. Classical distortion shapes are known as Compton-y and chemical potential (µ-type) distortions; however, recently it has been shown that more general distortions can be created at redshifts 10^4 < z < 3×10^5. This makes spectral distortions a unique and powerful probe of different early-universe processes. The immense potential of CMB spectral distortion measurements and their synergies with upcoming CMB anisotropy studies (Litebird, COrE+, Stage-IV CMB) has identified them as an important future target, with several innovative experimental concepts (e.g., PIXIE, APSERa) being actively discussed by the cosmology community. This proposal has one main goal: to transform the emerging field of CMB spectral distortions into a mature scientific discipline. The team will significantly expand and strengthen the spectral distortion science case with particular emphasis on novel time-dependent information from the recombination era (10^3 < z < 10^4) and various photon injection processes. By combining all available information, we will investigate what spectral distortions could teach us about early-universe physics and the cosmological ionization history. Novel foreground parameterizations and experimental setups will be studied and simulation pipelines will be developed. Our work could deliver new tests for inflation, reionization and particle physics as well as extend our ability to distinguish sources of different distortion signals in the presence of foregrounds. We will identify novel spectral distortion science goals that will drive the experimental designs of future CMB spectroscopy experiments, pioneering and facilitating spectral distortion activities in Europe and worldwide.

1 965 171 €

Start date: 2017-09-01, End date: 2022-08-31

Condensible substances, which undergo a phase change from gaseous to liquid or solid condensed form, have a profound impact on planetary atmospheres, and are central to the determination of most key aspects of a planet's climate. The three phases of water operating in Earth's present climate provide the archetype for condensible processes in climate dynamics, but the dawning age of exoplanet discovery and characterization requires that the understanding of phase change effects be expanded far beyond the situations familiar from the study of Earth's climate, or indeed of the climate of any Solar System planet. The goal of this project is to pioneer the advances needed to understand condensible climate dynamics for the vastly broader range of condensible substances, thermodynamic and planetary configurations presented by the growing catalogue of exoplanets. The emphasis will be on the smaller range of planets (super-Earth to Earth mass or size class), which need not have hydrogen-dominated atmospheres and therefore present a richer and highly challenging variety of possible condensible behavior. This class of planets includes all planets that are potentially habitable for Earthlike life, but even planets that are far from habitable shed light on essential features of planets in the Universe, and will be studied. The work will embrace both small scale buoyancy-driven turbulent convection and planetary scale circulations. Idealized numerical simulations, buttressed by theoretical analysis will be employed. Particular emphasis will be put on aspects of exoclimate that are amenable to probing by current observations and improved observational techniques likely to become available in the coming decade. Such properties include cloud properties observable through transit-depth spectra and dayside/nightside temperature and composition contrasts observable through phase curve observations.

2 492 565 €

Start date: 2017-10-01, End date: 2022-09-30

Galaxies are the building blocks of structure in the Universe; this proposal seeks to understand how their shapes, colours and dynamics are determined. For example, what happened in the history of some galaxies to transform them into passive ellipticals while others, seemingly of the same mass and in the same environment, are star-forming spirals? Even such a basic question about the link between morphology and star formation has not yet been answered, revealing our theories of galaxy formation are inadequate. This is a major concern in an era where understanding the shapes of galaxies and how they relate to the underlying dark matter is essential for progress in precision cosmology. This project will build the missing link between the history of a galaxy and its observational properties (i.e. between cause and effect) by using numerical simulations. Current research in this area rightly gives significant attention to the crucial problem of how feedback – energy input from supernovae, active galactic nuclei, and more – affect observable properties. But as well as investigating this avenue, GM Galaxies will uniquely make use of my new technique (“genetic modification”) to systematically investigate the role of the galaxy’s merging and accretion history at high resolution. To distinguish the fingerprints of history from the effects of feedback, we will compare to rich new data from integral field unit surveys; these reveal, for example, galactic metallicity and velocity maps. My pilot study for this project shows that such measures of a galaxy disambiguate between alternative formation routes to galaxies which would appear similar by photometric measures alone. Similarly, we will make predictions for the observable properties of the gas reservoir surrounding galaxies and for integral field observations at high redshift. In this way we will make a predictive account of how galactic structure is determined by the interaction of the accretion history with feedback.

1 741 230 €

Start date: 2019-10-01, End date: 2024-09-30

The ambition of this research program is to challenge the nature of gravity, provide an alternative to dark energy, and pave the way towards a potential resolution of one the most tantalizing problems of physics today: The Old Cosmological Constant Problem. As General Relativity celebrates its centennial, its predictive successes and its status as our most elegant theory of gravity are incontrovertible. Nevertheless, while the recent discovery of the late-time acceleration of the Universe is in perfect agreement with observations, the 120 orders of magnitude discrepancy between expectations and observations is one of today's most challenging puzzles and may be the sign of new physics to uncover. This conundrum has driven the development of dark energy models as alternative sources for acceleration, but many of them suffer from a similar discrepancy and require an unnatural tuning of their parameters. Despite decades of attempts, the Old Cosmological Constant Problem remains yet unsolved. This program proposes a distinct direction to address this problem and to explain the acceleration of the Universe where the graviton, the particle carrier of gravity, has a mass, or is effectively massive. Not only will this open a new panorama for cosmology, it will also answer the fundamental question of the nature of the graviton. Signatures and constraints will be derived through astrophysical and cosmological probes. While striving to address these fundamental challenges, the program will also elucidate new aspects of massive gravity by establishing its theoretical viability and embedding as an effective field theory. These developments will feed into new breakthroughs that have recently emerged from massive gravity. As major missions and experiments are underway to probe dark energy and to detect gravitational waves, there is no better time to question gravity at the fundamental level, to provide alternatives to dark energy and to determine their unique signatures.

1 975 829 €

Start date: 2017-05-01, End date: 2022-04-30