Kinematic reconstruction of Λ(t)CDM models

In this work, we have analysed two kinematic parametrizations for Λ( t )CDM models, namely, the linear expansions Λ ( z ) = Λ 0 + Λ 1 z and Q ( z ) = Q 0 + Q 1 z , where Q is the interaction term. In the case of the Q ( z ) parametrization, we have also tested the particular case of a constant interaction term, Q ( z ) = Q 0 . In order to constrain the free parameters of these models, we have used Cosmic Chronometers (CC), SNe Ia data (Pantheon+&SH0ES) and BAO data. As a general result, we have found weak constraints over the free parameters of the analysed models. In the case of Λ( z ), we have found for the Λ variation parameter, Ω Λ 1 ≡ Λ 1 3 H 0 2 = 0.02 ± 0.14 . In the case of the Q ( z ) parametrization, we have worked with the dimensionless interaction term Q ( z ) ≡ 8 π G Q ( z ) 3 H 0 3 , from which we have found Q 0 = 2.2 ± 2.7 and Q 1 = − 6.2 ± 7.6 . In the particular case of a constant interaction term, we have found Q 0 = 0.18 ± 0.7 . All these constraints are at 68% c.l. The constraints we have obtained are compatible with the standard ΛCDM model, although still providing a large margin for Λ variation.