# Statistics of null geodesics of photons on cosmological scales

Title of the project |
Statistics of null geodesics of photons on cosmological scales |

Primary and secondary scientific disciplines |
Astronomy, Atomic physics |

Description of the project |
Characteristics and main objectives of the research project:
· Light propagating through the Universe is bent because of its gravitational interaction with large scale structures. This bending of light results in the distortion of astronomical images called astronomical shear usually attributed to gravitational lenses. However, light’s trajectory is not only affected by the structures directly encountered on its path, but also by the ones lying outside of it, resulting in an enhancement of shearing effects. In Einstein’s theory of General Relativity, long-range interactions are described by the Weyl curvature tensor. The goal of the project is to study the contribution of the Weyl curvature to the generation and evolution of the image distortion in order to quantify its effects on cosmological observations. · A first phase, consisting of an analytical approach aimed at obtaining a first estimate of the magnitude of such effects, will be followed by numerical tests based on ray-tracing software in order to achieve a more quantitative estimate of the Weyl curvature contribution. The results will be compared with observations. · In the standard homogeneous model of cosmology, the Weyl curvature tensor is identically zero and therefore its effects are unaccounted for. Although small, in the era of precision cosmology, these effects might not be negligible. In fact, even a few percent correction could be important when estimating, for example, the mass of a cluster of galaxies from weak lensing. The project is conducted in cooperation with the University of Tasmania, Australia Principal supervisor: Prof. dr hab. Boudewijn Roukema |