ΛₛCDM cosmology from a type-II minimally modified gravity

We have successfully integrated ΛₛCDM, a promising model for alleviating cosmological tensions, into a theoretical framework by endowing it with a specific Lagrangian from the VCDM model, a type-II minimally modified gravity. In this theory, we demonstrate that an auxiliary scalar field with a linear potential induces an effective cosmological constant, enabling the realization of an abrupt mirror AdS-dS transition in the late universe through a piecewise linear potential. To eliminate the sudden singularity in this setup and ensure stable transitions, we smooth out this potential. Realized within the VCDM theory, the ΛₛCDM model facilitates two types of rapid smooth mirror AdS-dS transitions: (i) the agitated transition, associated with a smooth jump in the potential, where Λₛ, and consequently H, exhibits a bump around the transition's midpoint; and (ii) the quiescent transition, associated with a smooth change in the slope of the potential, where Λₛ transitions gracefully. These transitions are likely to leave distinct imprints on the background and perturbation dynamics, potentially allowing the observational data to distinguish between them. This novel theoretical framework propels ΛₛCDM into a fully predictive model capable of exploring the evolution of the Universe including the late-time AdS-dS transition epoch, and extends the applicability of the model. We believe further research is crucial in establishing ΛₛCDM as a leading candidate or guide for a new concordance cosmological model.