Cosmological constrains on fast transition Unified Dark Energy/Matter models

We explore the observational adequacy of a class of Unified Dark Energy/Matter (UDE/M) models with a fast transition. Our constraints are set using a combination of geometric probes, some low redshift ones, and some high redshift ones (CMB related included). The transition is phenomenologically modeled by two different transition functions corresponding to a fast and to an ultra-fast transition respectively. We find that the key parameters governing the transition can be well constrained, and from the statistical point of view it follows that the models cannot be discarded when compared to $Λ$CDM. We find the intriguing result that standard/input parameters such as $Ω_m$ and $Ω_b$ are far better constrained than in $Λ$CDM, and this is the case for the derived/output parameter measuring the deceleration value at present, $q_0$.

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