Late-time Universe, H₀-tension, and unparticles

ΛCDM is increasingly facing challenges in late-time cosmology, notably in the Hubble parameter H(z) at redshift zero, known as H₀-tension. There are various efforts to alleviate this tension mostly by models with extra parameters. We elaborate on unparticle cosmology as a modification for late-time ΛCDM mainly for its potential to alleviate H₀-tension. Unparticle cosmology proposes a scale invariant contribution by a dimensionless parameter δ. The ambiguities in the model demand for different avenues to inspect it and here we try some of them. The dynamical behavior of unparticle cosmology with and without Λ, shows that for most values of δ∈[ -6,1] (corresponding to d_U∈[-2,3/2]), the late-time universe will be Λ and matter dominated respectively, with negligible contribution of unparticles. It predicts H(z) in the future to be zero or constant, the latter pointing to a stable de Sitter phase for our universe. Our data analysis shows δ=-2.06±0.46 as the best fit to data ruling out the conventional value of d_U=3/2. However, there is a pronounced gap between the models and what is demanded by observational data, in qQ-diagram for all δ. We conclude that unparticle cosmology can not relax late-time ΛCDM challenges, but it provides a pointer to holographic limit of dark energy δ=-2.