Programme

P.4 -- Posters, VCTP-51

Date: Tuesday, 4 August 2026

Time: 09:30 - 10:30

Resolving Singularities in Sign-Changeable Interacting Dark Energy via Observational Constraints from Type Ia Supernovae

Dang Minh Nhut

Dalat University

Despite the remarkable phenomenological success of the standard $\Lambda$CDM cosmological model, it still exhibits many scientific gaps in both theoretical and observational aspects, particularly regarding the fine-tuning, cosmic coincidence, $H_0$ tension, and $S_8$ tension problems. Therefore, a new physical model beyond the $\Lambda$CDM paradigm is required. The Interacting Dark Energy (IDE) model, which assumes a non-gravitational interaction between dark energy (DE) and dark matter (DM), allows for the exchange of energy between them. Recent cosmological analyses indicate the possibility of a sign-changeable interaction, that is, the direction of energy transfer being reversed during evolution. However, the linear parametrization based on the Taylor expansion, $b(z) = b_0 + b_1 z$, diverges and creates unphysical singularities in the early Universe. To resolve physical inconsistencies and ensure convergence at high redshifts, this study investigates the dynamics of the sign-changeable IDE model through the Chevallier-Polarski-Linder (CPL) and Jassal-Bagla-Padmanabhan (JBP) parametrizations, directly confronting them with the standard linear model. A numerical framework is established to combine the theoretical system of equations with a dataset of 580 Type Ia Supernovae from the Union2.1 compilation through an optimization algorithm, in order to estimate the density parameters and related dynamical quantities. The results confirm that the CPL and JBP parametrizations not only fit observational data in the late Universe but also preserve thermodynamic stability in the early Universe, thus providing a phenomenological mechanism significantly superior to the conventional linear approach.

Presenter: Dang Minh Nhut