We propose a revised cosmological scenario that extends the $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) framework by incorporating metric $f(R)$ gravity in the Jordan frame. In this model, the dark energy component arises from a nonminimally coupled scalar field, decomposed into a smooth background [set to unity to recover general relativity (GR)] and a rapidly varying, massive fluctuation that decays into the dark matter sector. In the near-GR limit, this setup provides a phenomenological extension of $\mathrm{\Lambda }\mathrm{CDM}$ characterized by two additional parameters: the present-day value of the scalar fluctuation and a normalized decay rate. Using a Markov chain Monte Carlo analysis of low-redshift cosmological data, comprising Type Ia supernovae, baryon acoustic oscillation (BAO), and cosmic chronometer measurements, we find that the proposed model achieves a better overall fit than $\mathrm{\Lambda }\mathrm{CDM}$, while the Bayesian evidence remains statistically inconclusive given the inclusion of two extra parameters. The model predicts a moderate increase in the inferred value of $H_0$ and an improved consistency with Dark Energy Spectroscopic Instrument BAO data when adopting the SH0ES prior. Furthermore, describing dark matter particle creation as a transition phase in the late Universe offers an intriguing physical interpretation, potentially capturing features already present in current data and providing a promising avenue to explore extensions of the standard cosmological model within modified gravity frameworks.

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• Alternative gravity theories
• Cosmological parameters
• Dark matter
• Evolution of the Universe