Scalar fields are ubiquitous in string theory compactifications, arising from geometric moduli and as descendants of higher-dimensional form fields. In cosmology, they provide well-motivated frameworks for dynamical dark energy and interacting dark sectors, allowing for time-varying equations of state and an effective phantom behaviour, features that have recently attracted attention in connection with late-time deviations from ΛCDM.
At the same time, theoretical consistency places important conditions on the scalar potentials, couplings, and field-space geometry that can be realised in such models. Swampland considerations, fine-tuning issues, and stability criteria play a central role in evaluating their viability and offer a useful complement to purely phenomenological approaches.
In this talk I will present recent progress on single- and multi-scalar dark-energy models, including coupled dark sectors, and discuss their cosmological implications within a theoretically consistent framework. I will highlight how theoretical limitations may shape the space of viable models and where new dynamics may remain possible. I will also comment on how reconstruction approaches, including modern data-driven techniques, may help connect theoretical constraints to emerging observational trends.