Shedding light on the nature of dark matter and dark energy with multi-wavelength all-sky surveys
Despite two decades of intensive efforts after the discovery of the accelerating expansion of the Universe, the nature of dark energy that dominates 68 percent of the energy density remains unknown. The majority of the remainder is in dark matter. Similarly, the elementary particles which constitute its mass is unidentified. Galaxy clusters trace the highest peaks in the cosmic density field and offer an independent and powerful probe of the growth of structure. Their overall abundance on the sky is strongly dependent on underlying cosmology. With the new availability of all sky surveys of galaxy clusters in the X-ray band with eROSITA and the utility of weak lensing signal in accurate estimation of cluster masses, we are on the verge of constraining cosmology with percent level precision. We propose to measure the energy density of the total matter, the normalization of the power spectrum of dark energy, the dark energy equation-of-state, and neutrino masses with a percent level accuracy. All sky survey observation with eROSITA and complimentary weak lensing observations with HSC also offer new prospects to test general relativity at large scales, and constrain well-motivated dark matter models (e.g. warm dark matter and self-interacting dark matter). Europe will have an opportunity to be on the forefront of observational cosmology and set the stage for the upcoming experiments if this proposal is funded. Given my expertise in the field of galaxy clusters and my role as the chair of the clusters and cosmology working group of the eROSITA consortium, I am uniquely suited to lead this effort and accomplish the goals of this proposal.