Observational constraints on the deceleration parameter in a tilted
  universe
  We study a parametrization of the deceleration parameter in a tilted
universe, namely a cosmological model equipped with two families of observers.
The first family follows the smooth Hubble flow, while the second are the real
observers residing in a typical galaxy inside a bulk flow and moving relative
to the smooth Hubble expansion with finite peculiar velocity. We use the
compilation of Type Ia Supernovae (SnIa) data, as described in the Pantheon
dataset, to find the quality of fit to the data and study the redshift
evolution of the deceleration parameter. In so doing, we consider two
alternative scenarios, assuming that the bulk-flow observers live in the
$\Lambda$CDM and in the Einstein-de Sitter universe. We show that a tilted
Einstein-de Sitter model can reproduce the recent acceleration history of the
universe, without the need of a cosmological constant or dark energy, by simply
taking into account linear effects of peculiar motions. By means of a Markov
Chain Monte Carlo (MCMC) method, we also constrain the magnitude and the
uncertainties of the parameters of the two models. From our statistical
analysis, we find that the tilted Einstein-de Sitter model, equipped with one
or two additional parameters that describe the assumed large-scale velocity
flows, performs similar to the standard $\Lambda$CDM paradigm in the context of
model selection criteria (Akaike Information Criterion and Bayesian Information
Criterion).
