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 ACDM 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 ACDM model), one can derive that the equation of state of dark energy increases from-2/3 ln 10 -1 in the past to -1 in the future. We show that by setting a hard-cut 2 sigma lower bound prior for H-0 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), Ly alpha BAO, and cosmic microwave background (CMB)) substantially better than the concordance Lambda CDM model with Delta chi(2)(bf) similar to 41.08 and Delta DIC similar to -35.38. If there are no substantial systematics in SN Ia, BAO, or Planck CMB data, and assuming the reliability of current local H-0 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.