all projects tagged lensing

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.

The phase-space of the cosmic large-scale structure is only partially accessible to observations. The resolution of structures along the line of sight is particularly difficult in weak lensing observations, but also in galaxy surveys one deals with rather large radial uncertainties. For that purpose, we employ 3d-decompositions and investigate the observability of 3d-Fourier modes, in weak lensing and in cross-correlation with other tracers, and compute effects that are sensitive to large-scale velocity fields.

Constructive gravity asserts that there is a clear path of constructing a gravitational interaction for particles that is determined completely by their non-gravitational interactions. Our group works in cooperation with F.P. Schuller (Erlangen) and M.C. Werner (Kyoto) on cosmological tests of constructive gravity, and we work on astrophysical and cosmological applications of area-metric gravity, as well as on its conceptual construction.

Cosmic inflation is an early phase of accelerated expansion that solves the flatness-problem in FLRW-cosmologies and is a mechanism for introducing fluctuations in the distribution of matter. Of particular interest to us are inflationary non-Gaussianities and their measurement in future large-scale structure surveys. The best way of measuring higher-order non-Gaussianities is still unclear; while there is a clear way of computing polyspectra from covariant perturbation theory, their estimation from data quickly becomes a combinatorial problem, for which we use advanced sampling methods.

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. 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.

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.

Weak lensing operates under the assumption of intrinsically uncorrelated galaxy shapes, which might not be true because galaxies experience correlated tidal gravitational fields and share a similar angular momentum generation. We have worked on tidal interaction models for galaxies to derive ellipticity correlations for investigating their contaminating effect in weak lensing parameter inference. Starting from models of tidal shearing and tidal torquing for the orientation of elliptical and spiral galaxies, we are constructing more elaborate models for predicting and investigating intrinsic alignments, and hope to apply them to Euclid data.

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.