Reconstructing the cosmic expansion with a generalized q(z) parameterization: a decelerating Universe from late-time constraints.
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| Title: | Reconstructing the cosmic expansion with a generalized q(z) parameterization: a decelerating Universe from late-time constraints. |
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| Authors: | Verdugo, Tomás1 (AUTHOR) tomasv@astro.unam.mx, Hernández-Almada, Alberto2 (AUTHOR) ahalmada@uaq.mx, García-Aspeitia, Miguel A.3 (AUTHOR) angel.garcia@ibero.mx, Magaña, Juan4 (AUTHOR) juan.maga@ucentral.cl, Motta, Verónica5 (AUTHOR) veronica.motta@uv.cl |
| Source: | European Physical Journal C -- Particles & Fields. May2026, Vol. 86 Issue 5, p1-13. 13p. |
| Subjects: | Parameterization, Hubble constant, Redshift, Expanding universe, Physical cosmology, Universe, Metaphysical cosmology |
| 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 , 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 q 0 = - 0. 25 - 0.04 + 0.04 and a transition redshift 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 . The ERC remains weakly constrained by late-time data but ensures a smooth and monotonic evolution of q(z), j(z), and 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. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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| 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 , 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 q 0 = - 0. 25 - 0.04 + 0.04 and a transition redshift 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 . The ERC remains weakly constrained by late-time data but ensures a smooth and monotonic evolution of q(z), j(z), and 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. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 14346044 |
| DOI: | 10.1140/epjc/s10052-026-15766-1 |
