Bound Dark Energy: towards understanding the nature of the Dark Energy

Abstract: We present a complete analysis of the observational constraints and cosmological implications of our Bound Dark Energy (BDE) model aimed to explain the late-time cosmic acceleration of the universe. BDE is derived from particle physics and corresponds to the lightest meson field $\phi$ dynamically formed at low energies due to the strong gauge coupling constant. The evolution of the dark energy is determined by the scalar potential $V(\phi)=\Lambda_c<sup>{4+2/3}\phi<sup>{-2/3}$ arising from non-perturbative effects at a condensation scale $\Lambda_c$ and scale factor $a_c$, related each other by $a_c\Lambda_c/\mathrm{eV}=1.0934\times 10<sup>{-4}$. We present the full background and perturbation evolution at a linear level. Using current observational data, we obtain the constraints $a_c=(2.48 \pm 0.02)\times10<sup>{-6}$ and $\Lambda_c=(44.09 \pm 0.28) \textrm{ eV}$, which is in complete agreement with our theoretical prediction $$\Lambda_c^{{th}=34^{{+16}_{-11}\textrm{}} eV}$$. The bounds on the equation of state today, the dark energy density and the expansion rate are $w_\mathrm{BDE 0}=-0.929\pm 0.007$, $\Omega_\mathrm{BDE0}=0.696\pm0.007$ and $H_0=67.82\pm 0.05$ km s$<sup>{-1}$Mpc, respectively. Even though the constraints on the six Planck base parameters are consistent at the 1$\sigma$ level between BDE and the concordance $\Lambda$CDM model, BDE improves the likelihood ratio by 2.1 of the Baryon Acoustic Oscillations (BAO) measurements with respect to $\Lambda$CDM and has an equivalent fit for type Ia supernovae and the Cosmic Microwave Background data. We present the constraints on the different cosmological parameters, and particularly we show the tension between BDE and $\Lambda$CDM in the BAO distance ratio $r_\mathrm{BAO}$ vs $H_\mathrm{0}$ and the growth index $\gamma$ at different redshifts, as well as the dark matter density at present time $\Omega_ch<sup>2$ vs $H_0$.