Interacting scalar fields as Dark Energy and Dark Matter in Einstein scalar Gauss Bonnet gravity

Abstract A Gauss-Bonnet (GB) coupled scalar field ϕ , responsible for the late-time cosmic acceleration and interacting with a coherent scalar field ψ through an interaction potential W ( ϕ,ψ ), is considered from the point of view of particle physics for two different models. The non-minimal coupling between the GB curvature term and the field ϕ leads to a time-dependent speed of gravitational waves (GWs), which is fixed to unity in order to be consistent with current GW observations, rendering the GB coupling function model-independent. We investigate the dynamical stability of the system by formulating it as an autonomous system, and provide a detailed discussion on the choice of initial conditions required to obtain stable background evolution of the models. We constrain the model parameters using various sets of observational data, including both early- and late-time probes. We incorporate the improved Dark Energy Survey (DES) 5-year Type Ia supernova sample (DES-SN5YR), referred to as DES-Dovekie, which exhibits substantially lower tension with the Pantheon+ supernova sample. We find that both models are physically viable and closely follow the ΛCDM trend for the Pantheon+ and DES samples. However, upon including the Roman mock data, a significant departure is observed at higher redshifts, yielding statistically strong preference over the flat ΛCDM model.