The Sign-Switching of the Cosmological Constant

TL;DR

This paper introduces and analyzes models where the cosmological constant changes sign over cosmic history, exploring their theoretical background, perturbation evolution, and observational viability compared to standard models.

Contribution

It presents a unified framework for sign-changing cosmological constants, including both ladder-step and smooth transition models, with detailed perturbation analysis and observational comparisons.

Findings

Sign-changing models can fit current data as well as ΛCDM.

Distinctive signatures in structure formation from the sign transition.

Viability of dynamic, sign-changing dark energy models.

Abstract

We propose and investigate a class of dynamical dark energy models in which the cosmological constant evolves from negative values in the early Universe to a positive value at low redshifts. This framework includes a generalised ladder-step evolution, as well as smooth-transition scenarios, providing a unified description of sign-changing cosmological constants. We analyse the theoretical construction and background dynamics of these models using cosmographic diagnostics. Extending this study to the linear perturbation regime, we solve the perturbation equations from the radiation-dominated era with adiabatic initial conditions. We examine the evolution of the matter density contrast, gravitational potential, and the $f\sigma_8$ observable. Our results are compared against the standard $\Lambda$CDM model and confronted with current observational data, illustrating the phenomenological viability of sign-changing dark energy models and revealing distinctive imprints on cosmic structure formation arising from the transition of the cosmological constant.