Speaker
Description
The YONSEI group [MNRAS 544 (2025) 975] recently proposed a progenitor age-bias correction to Type Ia supernovae. Applying this empirical correction, we find that the Pantheon+ and DES5Y Hubble diagrams converge toward the special Kolb point $(w, \Omega_m)=(-1/3,0)$ in the flat $w$CDM parameter space. This point yields the compact zero-parameter logarithmic luminosity-distance relation $d_L=\frac{c}{H_0}(1+z)\ln(1+z)$, with $H_0$ calibrated to Cepheids. The $\ln(1+z)$ factor accounts for the excess moduli observed in high-redshift SNe Ia without requiring dark energy. Remarkably, the Kolb point is also consistent with the very recent H II-galaxy observations extending to $z∼14$ [Chávez et al., arXiv:2607.14254]. Within conventional GR, however, the Kolb point requires an unusual K-matter equation of state $w=-1/3$. Moreover, dynamical dark energy, such as the CPL parametrization, has become a default ad hoc model choice. To avoid both of these quandaries, we propose an alternative route in which the speed of light becomes dynamical during cosmic expansion rather than invoking a dynamical dark-energy sector. In the Dolgov–Barrow class of cosmologies, $a\propto t^\mu$ and $c\propto a^{-\zeta}$, the same logarithmic luminosity-distance relation arises naturally along the scale-invariant branch $(1+\zeta)\,\mu=1$, which leads to a non-trivial kinematic relation $c=\frac{c_0}{H_0}\dot a$ between the speed of light and the cosmic expansion rate. The 1998 discovery of cosmic acceleration therefore need not imply dark energy, but may instead point toward a scale-invariant Dolgov–Barrow cosmology in which the speed of light becomes dynamical on an expanding cosmic background.
| Topic | Cosmology, gravitational waves, dark energy, and dark matter |
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