An interpretation of Hubble tension and S8 tension by the observed Inhomogeneous matter density






二間瀬 敏史 名誉教授(東北大学)






Hubble parameter describes the expansion rate of the universe and is one of the most important parameter to characterize our universe. Thus, the measurement has been a major topic in the observational cosmology. Recently there has been a significant discrepancy in the measured value depending on the method of the observation. This is called as the Hubble tension. If the discrepancy is real, it will cause a revolutionary change in the standard cosmology. Not only Hubble parameter but also recent galaxy survey reported a similar discrepancy in the structure formation parameter S8 from CMB measurement. On the other hand, there is observational evidence by the observation of K-band luminosity density that our galaxy is in a low-density region of the order of three hundred Mega parsec. We consider the effects of this inhomogeneous matter distribution on the Hubble parameter and S8 parameter. For this purpose, Einstein equation is averaged over an arbitrary finite region to construct local Friedman universe which is characterized by local cosmological parameters, and thus we can derive the relation between local and horizon scale cosmological parameters. According to this relation we can explain the observed discrepancies of Hubble parameter and S8 without introducing any new physics.