all projects tagged dark energy

gravity on large scales


We work on the design of tests of specific, non-standard tests of gravity on galactic scales like screening-mechanisms. Furthermore, we investigate possible signatures of post-Newtonian gravity in cosmological surveys, and how general relativistic effects can be observed in cosmology (with G.F. Lewis, Sydney and K. Bolejko, Tasmania).



The European Euclid mission is a space-based large-scale structure survey, where we are involved in the weak lensing programme, where we construct and test models of intrinsic alignments of galaxies, which result due to tidal interaction with the large-scale structure or by correlations in the initial conditions of structure formation. In addition, our group was active in computing second order effects in gravitational lensing, parameter estimation biases and the information content of Gaussian and non-Gaussian weak lensing maps.



The fluctuation pattern of the temperature and polarisation of the cosmic microwave background gets distorted by weak lensing deflection and changes therefore its correlation properties. Our group is interested in higher-order effects in lensing and cross-correlations between the lensing effect and other probes of the cosmic large-scale structure. For small-scale CMB-lensing our cooperation partners are V.M. Böhm (Berkeley) and S. Hagstotz (Stockholm). From a methodical point of view closely related is the question of lensing of the 21cm background, which however involves more aspects of non-Gaussianity and reionisation history, including its non-uniformity.

statistical inference and information geometry


Modern cosmology is a statistical science and we are interested in questions related to the information content of large-scale structure surveys, in particular in the nonlinear regime, selection of models and the effect of systematical errors on the parameter estimation and model selection process. In particular, we investigate what properties about gravity are in principle knowable from cosmological surveys, how non-Gaussian structures can be described in an efficient way and how information about fundamental physics can be extracted from non-Gaussian structures.

weak gravitational lensing


Weak lensing refers to the weak distortion of the light bundles reaching us from distant galaxies caused by tidal gravitational fields in the cosmic large-scale structure. Weak lensing is an excellent tool for investigating gravity on large scales, and we have worked on tomographic methods, cross-correlations and higher-order statistics of the weak lensing signal, as well as effects gravitational light deflection at second order. We would like to understand how one can reach a precision prediction of the weak lensing signal, how one can use the lensing signal as a cosmoogical probe, and what statistical properties the lensing signal has.

integrated Sachs-Wolfe effect


The iSW-effect is a secondary CMB-anisotropy and can be used to measure the equation of state of dark energy. Our results on the iSW-effect include the extension to nonlinearly evolving structures (Rees-Sciama-effect), the interpretation of the iSW-effect as a higher-order lensing phenomenon and cross-correlations with the weak lensing field. Using data from the European Planck-satellite, we have obtained independent measurements on the existence and properties of dark energy, in cooperation with P. Vielva (Santander) and C. Hernandez-Monteagudo (Teruel).



The Planck-surveyor satellite was a European CMB-mission that mapped out the temperature and polarisation fluctuations to angular scales of a few arcminutes. We added Sunyaev-Zel’dovich simulations to the Planck-sky model, as well as adopting maps of the vibrational transitions of carbon monoxide and of the free-free-emission due to direct interaction between electrons. In analysing the data, we obtained independent information on dark energy from the measurement of the integrated Sachs-Wolfe effect (together with P. Vielva and C. Hernandez-Monteagudo).