http://arxiv.org/abs/1906.08275
Motivated by the current status of the cosmological observations and significant tensions in the estimated values of some key parameters assuming the standard $\Lambda$CDM 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 the later times. Theoretically, in this phenomenological dark energy model that has zero degree of freedom (similar to $\Lambda$CDM model), one can derive that the equation of state of dark energy increases from $-\frac{2}{3 {\rm{ln}}\, 10} -1$ in the past to $-1$ in the future. We show that setting a hard cut 2$\sigma$ lower bound prior for the $H_0$ that associates with $97.72\%$ probability from the recent local observations (Riess et al. 2019), this model can satisfy different combination of cosmological observations at low and high redshifts (SNe Ia, BAO, Ly{$\alpha$} BAO and CMB) substantially better than the concordance $\Lambda$CDM model with $\Delta \chi^2_{bf} \sim -41.08$ and $\Delta\,{\rm{DIC}} \sim-35.38$. With hard cut 1$\sigma$ lower bound $H_0$ prior associated with $84.13\%$ probability, our proposed phenomenologically emergent dark energy model can result to $\Delta \chi^2_{bf} \sim -88.5$ and $\Delta\,{\rm{DIC}} \sim-94.1$ with respect to $\Lambda$CDM model and $\Delta \chi^2_{bf} \sim-0.4$ and $\Delta\,{\rm{DIC}}\sim-27.5$ with respect to $w_0$-$w_a$ parameterization. If there is no substantial systematics in any of the data and assuming reliability of the current local $H_0$ measurements, there is a very high probability that with more precise measurement of the Hubble constant our proposed phenomenological model rules out the cosmological constant with decisive statistical significance. This simple phenomenologically emergent dark energy model can guide theoretically motivated dark energy model building activities.
X. Li and A. Shafieloo
Fri, 21 Jun 19
25/56
Comments: 7 pages, 4 figures, 1 table
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