Quantum field theoretic approaches to dark energy: Models and challenges

Abstract

Quantum Field Theoretic (QFT) approaches to dark energy aim to explain the observed accelerated expansion of the universe through fundamental principles of quantum physics and field dynamics. One of the central frameworks involves the concept of vacuum energy, arising from zero-point fluctuations of quantum fields. However, a major challenge—known as the cosmological constant problem—emerges from the vast discrepancy between theoretically predicted vacuum energy density and its observed value. To address this, alternative models such as dynamical scalar fields (e.g., quintessence, k-essence, and phantom energy) have been proposed, where dark energy evolves over cosmic time rather than remaining constant. QFT-based approaches also explore modifications of standard field theories, including effective field theory (EFT) formulations and interactions between dark energy and dark matter sectors. These models attempt to maintain consistency with observational constraints from cosmic microwave background (CMB), large-scale structure, and supernova data. Furthermore, approaches rooted in quantum gravity, such as holographic dark energy and vacuum decay models, provide deeper insights into the possible unification of quantum mechanics and cosmology. Despite significant progress, multiple theoretical and observational challenges persist, including fine-tuning issues, stability conditions, and the lack of direct experimental verification. The integration of QFT with cosmological observations remains an active area of research, with future surveys expected to constrain models more tightly. Overall, QFT offers a rich and promising framework, yet a complete and consistent explanation of dark energy remains elusive.