Growth of Matter Perturbations in the Bi-Galileons Field Model
  We study a dark energy cubic bi-Galileons field model based on truncation of
the recently proposed generalized covariant multi-Galileons model. We
investigate the cosmological dynamic of the model by the theory of dynamical
systems through the analysis of the properties of the fixed points in each
cosmological epoch.
  We show the existence of two tracker solutions, one of which is that of the
cubic single Galileon model and the other solution is the signature of the
second Galileon field. Exploiting the competition between the two Galileon
fields, we find a dark energy solution that avoids the approach to the tracker
solution with dark energy equation of state $w_{DE}=-2$ during the matter epoch
which is disfavored by the observational data. We study also the growth rate of
matter perturbations.
  Using recent $f\sigma_{8}$ redshift space distortion (RSD) and
model-independent observational Hubble (OHD) data sets, we place observational
constraints on the coupling constant and cosmological parameters of the
bi-Galileons model through Monte Carlo numerical method based on the
Metropolis-Hastings algorithm.
  We find that the amplitude of growth matter fluctuations is consistent with
the Planck15 data and ease the tension between early and later clustering, and
fits better the data from the DES survey over the data from KiDS-450 survey. We
also find that the best fit value for the Hubble constant is compatible with
new measurements of Cepheid-supernovae distance scale.
  Finally, we perform a model selection through the Bayes factor and found that
the bi-Galileons model is disfavored in comparison to the $\Lambda$CDM model,
but slightly preferred to $w$CDM model.
