Geometrical observational bounds on a fractal horizon holographic dark energy

A novel fractal structure for the cosmological horizon, inspired by COVID-19 geometry, which results in a modified area entropy, is applied to cosmology in order to serve dark energy. The constraints based on a complete set of observational data are derived. There is a strong Bayesian evidence in favor of such a dark energy in comparison to a standard $\mathrm{\Lambda }\mathrm{CDM}$ model and that this energy cannot be reduced to a cosmological constant. Besides, there is a shift toward smaller values of baryon density parameter and toward larger values of the Hubble parameter, which reduces the Hubble tension.

Figure 1

Evolution with time of (top panel) dimensionless density parameters for Barrow holographic dark energy, with the Hubble radius as boundary, $\mathrm{\Delta }=1$, ${\mathrm{\Omega }}_m=0.317$, ${\mathrm{\Omega }}_r=8.4\times {10}^{-5}$, $H_0=70.5\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$, and $C=2$, and (bottom panel) BH dark energy effective equation of state parameter. Colors: matter (blue), dark energy (black).

Figure 2

Normalized histograms for each cosmological parameter. In green: late-time analysis; in blue: full cosmological dataset. Dashed: $\mathrm{\Lambda }\mathrm{CDM}$ model; solid: Barrow holographic dark energy.

Figure 3

Joint contours for the Barrow holographic dark energy parameters (left panel) and for the baryonic density parameter vs Hubble constant (right panel). In green: late-time analysis; in blue: full cosmological dataset. Hard colors: 68% confidence levels; soft colors: 95% confidence levels. Dashed: $\mathrm{\Lambda }\mathrm{CDM}$ model; solid: Barrow holographic dark energy.

Figure 4

Evolution with time of dimensionless density parameters. (left panel) Matter (blue), baryons (red) and dark energy (grey/black) for both full BH model ($1\sigma$ confidence levels as shaded regions) and full $\mathrm{\Lambda }\mathrm{CDM}$ (dashed lines). (right panel). Evolution of dark energy: full BH model ($1\sigma$ confidence levels as shaded regions and best fit as solid black line) vs full $\mathrm{\Lambda }\mathrm{CDM}$ (dashed line).

Figure 5

Evolution of dark energy at different times. In green: late-time analysis; in blue: full cosmological dataset. Dashed: $\mathrm{\Lambda }\mathrm{CDM}$ model; shaded regions: Barrow holographic dark energy ($1\sigma$ confidence levels).