Cosmological constraints on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mi mathvariant="normal">Λ</mml:mi> <mml:mi mathvariant="normal">s</mml:mi> </mml:msub> <mml:mi>CDM</mml:mi> </mml:math> scenario in a type II minimally modified gravity

Abstract

The idea of a rapid sign-switching cosmological constant (mirror AdS-dS transition) in the late universe at $z\ensuremath{\sim}1.7$, known as the ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{s}}\mathrm{CDM}$ model, has significantly improved the fit to observational data and provides a promising scenario for alleviating major cosmological tensions, such as the ${H}_{0}$ and ${S}_{8}$ tensions. However, in the absence of a fully predictive model, implementing this fit required conjecturing that the dynamics of the linear perturbations are governed by general relativity. Recent work embedding the ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{s}}\mathrm{CDM}$ model with the Lagrangian of a type II minimally modified gravity known as VCDM has propelled ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{s}}\mathrm{CDM}$ to a fully predictive model, removing the uncertainty related to the aforementioned assumption; we call this new model ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{s}}\mathrm{VCDM}$. In this work, we demonstrate that not only does ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{s}}\mathrm{CDM}$ fit the data better than the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model, but the new model, ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{s}}\mathrm{VCDM}$, performs even better in alleviating cosmological tensions while also providing a better fit to the data, including cosmic microwave background, baryon acoustic oscillations, type Ia supernovae, and cosmic shear measurements. Our findings highlight the ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{s}}\mathrm{CDM}$ framework, particularly the ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{s}}\mathrm{VCDM}$ model, as a compelling alternative to the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model, especially by successfully alleviating the ${H}_{0}$ tension. Additionally, these models predict higher values for ${\ensuremath{\sigma}}_{8}$, indicating enhanced structuring, albeit with lower present-day matter density parameter values and consequently reduced ${S}_{8}$ values, alleviating the ${S}_{8}$ tension as well. This demonstrates that the data are well fit by a combination of background and linear perturbations, both having dynamics differing from those of $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$. This paves the way for further exploration of new ways for embedding the sign-switching cosmological constant into other models.

Topics & Concepts