2026/07/20 by Pranav Prasanthan, Hussain Gohar, Vincenzo Salzano
#gr-qc #astro-ph.CO
We constrain the class of modified cosmologies derived in Paper I [1] from a generalized mass-to-horizon relation (MHR) that enforces thermodynamic consistency between the Cai-Kim horizon temperature and generalized horizon entropies. The modified Friedmann equations depend on an entropy exponent m, an MHR coupling parameter γ, and an entanglement-correction amplitude fB, with standard ΛCDM recovered in the appropriate limit. Using Pantheon+/SH0ES Type~Ia supernovae, cosmic chronometers, DESI DR2 baryon acoustic oscillations, and Planck 2018 CMB distance priors, we constrain eight physically motivated sub-cases via Markov chain Monte Carlo and compare models through the Bayesian log-evidence. The entropy exponent is tightly bounded, |m-1|\lesssim O(10-4) when the MHR coupling is fixed (γ=1), relaxing to O(10-3) along the m-γ degeneracy, excluding any macroscopically significant departure from standard horizon thermodynamics. Freeing the MHR coupling parameter or the entanglement amplitude raises the inferred Hubble constant to h≃0.70-0.71, reducing the CMB-SH0ES tension from ∼4σ to ∼1.2-2.6σ, but no scenario fully resolves it within a flat universe. The Bayesian log-evidence nevertheless disfavors every extension relative to ΛCDM in all dataset combinations (-16\lesssimΔln Z \lesssim-1): the improved fits obtained when the SH0ES calibration is included reflect an absorption of the Hubble tension by the additional parameters rather than genuine evidence for modified horizon entropy.