Despite the availability of several cosmological models alternative to the standard LCDM, and the presence of observational tensions in the context of this model, still no alternative is preferred over standard cosmology. This might indicate that in order to solve the current observational issues, one might need to relax some of the fundamental assumptions that are at the foundation of the LCDM model. A direct consequence of some of these assumptions is the Distance Duality Relation (DDR), relating the different cosmological distances with each other, which might breakdown in extended theories, e.g. when photons are coupled to beyond standard model particles. In this talk I will discuss how upcoming cosmological surveys will be able to improve current constraints on the DDR, showing both the impact of observational improvements and how new observational windows (standard sirens and strong lensing) will provide new opportunities and new challenges.
Sajad Abbar