Late-time Universe, H-0-tension, and unparticles

Abstract

Lambda cold dark matter (Lambda CDM) is increasingly facing challenges in late-time cosmology, notably in the Hubble parameter H(z) at redshift zero known as H-0-tension. Extensions to Lambda CDM have been approached mostly by models with an extra parameter. In this work, we provide a framework for evaluating the viability of models of late-time cosmology by investigating unparticle cosmology as a case study. Unparticle cosmology proposes a scale invariant contribution by a dimensionless parameter delta. We focus on H-0-tension in comparison with scale invariant and Lambda CDM models. The dynamical behavior of unparticle cosmology with and without a cosmological constant shows that for most values of delta is an element of [-6, 1] (corresponding to d(u) is an element of[-2, 3/2]), the late-time Universe will be. and matter dominated, respectively, with negligible contribution of unparticles. It predicts HozTHORN in the future to be zero or constant, the latter pointing to a stable de Sitter phase for our Universe. Our data analysis shows delta = -2.06 +/- 0.46 as the best fit to the data. Consequently, the conventional value of d(u) = 3/2 equivalent to delta = 1 is ruled out by 6.6 sigma. However, there is a pronounced gap between the models and what is demanded by observational data in the qQ-diagram for all delta. We conclude that unparticle cosmology fails to come to the rescue of challenges to latetime Lambda CDM, but it provides a pointer to holographic dark energy.