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We study the background cosmology of the ghost-free, bimetric theory ofgravity. We perform an extensive statistical analysis of the model using bothfrequentist and Bayesian frameworks and employ the constraints on the expansionhistory of the Universe from the observations of supernovae, the cosmicmicrowave background and the large scale structure to estimate the model'sparameters and test the goodness of the fits. We explore the parameter space ofthe model with nested sampling to find the best-fit chi-square, obtain theBayesian evidence, and compute the marginalized posteriors and meanlikelihoods. We mainly focus on a class of sub-models with no explicitcosmological constant (or vacuum energy) term to assess the ability of thetheory to dynamically cause a late-time accelerated expansion. The modelbehaves as standard gravity without a cosmological constant at early times,with an emergent extra contribution to the energy density that converges to acosmological constant in the far future. The model can in most cases yield verygood fits and is in perfect agreement with the data. This is because manypoints in the parameter space of the model exist that give rise totime-evolution equations that are effectively very similar to those of the$\Lambda$CDM. This similarity makes the model compatible with observations asin the $\Lambda$CDM case, at least at the background level. Even though ourresults indicate a slightly better fit for the $\Lambda$CDM concordance modelin terms of the $p$-value and evidence, none of the models is statisticallypreferred to the other. However, the parameters of the bigravity model are ingeneral degenerate. A similar but perturbative analysis of the model as well asmore data will be required to break the degeneracies and constrain theparameters, in case the model will still be viable compared to the$\Lambda$CDM.

Accelerated expansion from ghost-free bigravity: a statistical analysis with improved generality