Abstract We present a generalized phenomenological parameterization of the deceleration parameter q (z) that incorporates an effective radiative component (ERC) in addition to a localized late-time contribution. The proposed framework extends previous two-parameter q (z) reconstructions by explicitly regulating the high-redshift behavior while preserving the late-time transition dynamics. We constrain the free parameters (h, q₀, zc, zₑ) (h, q 0, z c, z e) using late-time observational data from cosmic chronometers (CC), Pantheon+ Type Ia supernovae (SNIa), H ii galaxies (HIIG), and intermediate-luminosity quasars (QSO). For the full data combination (CC+SNIa+HIIG+QSO), we obtain q₀ = -0. 25^+0. 04-₀. ₀₄ q 0 = - 0. 25 - 0. 04 + 0. 04 and a transition redshift zT 0. 80 z T ≃ 0. 80, indicating a currently accelerating Universe with a transition occurring earlier than in the Λ CDM model. Within the redshift range probed by the data, the reconstructed q (z) deviates from the Λ CDM trend, suggesting a possible reduction of the late-time acceleration. Furthermore, the reconstruction favors a relatively high value of the Hubble parameter, h = 0. 729 0. 006 h = 0. 729 ± 0. 006. The ERC remains weakly constrained by late-time data but ensures a smooth and monotonic evolution of q (z), j (z), and wₑff (z) w eff (z) across a wide redshift range. Within the observed interval, the model effectively reproduces the late-time behavior of the previous parametrization, while providing a controlled extension toward early epochs. Our results show that current low- and intermediate-redshift data are compatible with a reduced late-time acceleration.
Verdugo et al. (Mon,) studied this question.
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