Cosmological constraints on holographic dark energy models under the energy conditions

Abstract

We study the holographic and agegraphic dark energy models without interaction using the latest observational Hubble parameter data , the Union2.1 compilation of type Ia supernovae , and the energy conditions. Scenarios of dark energy are distinguished by the cutoff of cosmic age, conformal time, and event horizon. The best-fit value of matter density for the three scenarios almost steadily located at ${\ensuremath{\Omega}}_{m0}=0.26$ by the joint constraint. For the agegraphic models, they can be recovered to the standard cosmological model when the constant $c$ which presents the fraction of dark energy approaches to infinity. Absence of the upper limit of $c$ by the joint constraint demonstrates the recovery possibility. Using the fitted result, we also reconstruct the current equation of state of dark energy at different scenarios, respectively. Employing the model criteria ${\ensuremath{\chi}}_{\mathrm{min}}^{2}/\mathrm{dof}$, we find that conformal time model is the worst, but they cannot be distinguished clearly. Comparing with the observational constraints, we find that the strong energy condition is fulfilled at redshift $0.2\ensuremath{\lesssim}z\ensuremath{\lesssim}0.3$ with $1\ensuremath{\sigma}$ confidence level. We also find that the null energy condition gives a meaningful constraint for the event horizon cutoff model, especially compared with observational Hubble parameter data only. We note that the energy condition maybe could play an important role in the interacting models because of different degeneracy between ${\ensuremath{\Omega}}_{m}$ and constant $c$.