Quintessence arising from exponential potentials

TL;DR

The paper investigates quintessence driven by exponential potentials that can arise from higher-dimensional/string theory compactifications to explain the observed cosmic acceleration without a cosmological constant. It shows that exponential potentials admit attractor solutions (scaling and scalar-field-dominated) and that a sum of two exponentials can realize a transition from a radiation/matter-dominated era to late-time acceleration for natural parameter ranges. With nucleosynthesis constraints requiring steep slopes, $\alpha>5.5$, the model can achieve today’s equation of state $w_Q< -0.8$ and $\Omega_Q\approx 0.7$; if a negative $\beta$ is included, a minimum emerges leading to a de Sitter-like epoch. The paper also discusses assisted quintessence in multi-field setups, which increases the effective slopes and broadens the viable parameter space. Overall, the approach links quintessence to string-inspired potentials and presents a simple, robust mechanism for dark-energy dynamics, while noting challenges in obtaining the required slopes from particle physics.

Abstract

We demonstrate how exponential potentials that could arise in the early Universe as a result of Kaluza-Klein type compactifications of string theory, can lead to cosmological solutions which correspond to the currently observed accelerating Universe. The idea is simple, relying solely on the known scaling properties associated with exponential potentials. In particular we show that the existence of stable attractor solutions implies that the results hold for a wide range of coupling constants and initial conditions.

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