Constraining the runaway dilaton and quintessential dark energy

TL;DR

This paper investigates a dynamic dark energy model driven by a scalar dilaton field, constraining its parameters using observational data, and finds that it can include the cosmological constant within current uncertainties.

Contribution

It introduces a phenomenological ansatz for the dilaton field inspired by string theory, and constrains its parameters using observational data, linking it to dark energy properties.

Findings

Model parameters are tightly constrained by current data.

The model's predictions include the cosmological constant within 1σ errors.

Constraints on dark energy/dark matter couplings are established.

Abstract

Dark Energy is some of the weirdest and most mysterious stuff in the universe that tends to increase the rate of expansion of the universe. Two commonly known forms of dark energy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli whose energy density can vary with time. We explore one particular model for dynamic dark energy; quintessence driven by a scalar dilaton field. We propose an ansatz for the form of the dilaton field, $|\phi(a)|/m_P \equiv \alpha_1 \ln t+ \alpha_2 t^n=\alpha\ln a+ \beta\, a^{2\zeta}$, where $a$ is the scale factor and $\alpha$ and $\zeta$ are parameters of the model. This phenomenological ansatz for $\phi$ can be motivated by generic solutions of a scalar dilaton field in many effective string theory and string-inspired gravity models in four dimensions. Using a compilation of current data including type Ia supernovae, we impose observational constraints on the slope parameters like $\alpha$ and $\zeta$ and then discuss the relation of our results to analytical constrains on various cosmological parameters, including the dark energy equation of state. Sensible constraints are imposed on model parameters like $\alpha$ and $\zeta$ as well as on the dark energy/dark matter couplings using results from structure formation. The constraints of this model are shown to encompass the cosmological constant limit within $1\sigma$ error bars.