A Simple Phenomenological Emergent Dark Energy Model can Resolve the Hubble Tension

Motivated by the current status of cosmological observations and significant tensions in the estimated values of some key parameters assuming the standard ΛCDM model, we propose a simple but radical phenomenological emergent dark energy model where dark energy has no effective presence in the past and emerges at later times. Theoretically, in this phenomenological dark energy model with zero degrees of freedom (similar to a ΛCDM model), one can derive that the equation of state of dark energy increases from $-\tfrac{2}{3\mathrm{ln}\,10}-1$ in the past to −1 in the future. We show that by setting a hard-cut 2σ lower bound prior for H0 associated with a 97.72% probability from recent local observations, this model can satisfy different combinations of cosmological observations at low and high redshifts (SNe Ia, baryon acoustic oscillation (BAO), Lyα BAO, and cosmic microwave background (CMB)) substantially better than the concordance ΛCDM model with ${\rm{\Delta }}{\chi }_{{bf}}^{2}\sim -41.08$ and Δ DIC ∼ −35.38. If there are no substantial systematics in SN Ia, BAO, or Planck CMB data, and assuming the reliability of current local H0 measurements, there is a very high probability that with more precise measurements of the Hubble constant our proposed phenomenological model rules out the cosmological constant with decisive statistical significance and is a strong alternative to explain the combination of different cosmological observations. This simple phenomenologically emergent dark energy model can guide theoretically motivated dark energy model building activities.