Cosmological Constraints on Higgs-Dilaton Inflation
We test the viability of the Higgs-dilaton model (HDM) compared to the evolving dark energy ($w_0 w_a$CDM) model, in which the cosmological constant model $\Lambda$CDM is also nested, by using the latest cosmological data that includes the cosmic microwave background temperature, polarization and lensing data from the \textit{Planck} satellite (2015 data release), the BICEP and Keck Array experiments, the Type Ia supernovae from the JLA catalog, the baryon acoustic oscillations from CMASS, LOWZ and 6dF, the weak lensing data from the CFHTLenS survey and the matter power Spectrum measurements from the SDSS (data release 7). We find that the values of all cosmological parameters allowed by the Higgs-dilaton inflation model are well within the \textit{Planck} satellite (2015 data release) constraints. In particular, we have that $w_0 = -1.0001^{+0.0072}_{-0.0074}$, $w_a = 0.00^{+0.15}_{-0.16}$, $n_s = 0.9693^{+0.0083}_{-0.0082}$, $\alpha_s = -0.001^{+0.013}_{-0.014}$ and $r_{0.05} = 0.0025^{+0.0017}_{-0.0016}$ (95.5\%C.L.). We also place new stringent constraints on the couplings of the Higgs-dilaton model and we find that $\xi_{\chi} < 0.00328$ and $\xi_h / \sqrt{\lambda} = 59200^{+30000}_{-20000}$ (95.5\%C.L.). Furthermore, we report that the HDM is at a slightly better footing than the $w_0 w_a$CDM model, as they both have practically the same chi-square, i.e. $\Delta \chi^2 = \chi^2_{w_0 w_a\mathrm{CDM}}-\chi^2_{\mathrm{HDM}}=0.18$, with the HDM model having two fewer parameters. Finally Bayesian evidence favors equally the two models, with the HDM being preferred by the AIC and DIC information criteria.