Solar System and Atomic Clock Bounds on Locally Coupled Swampland Scalars

We study how local measurements can constrain light scalar fields that are relevant for late time cosmic acceleration and are often discussed in connection with swampland criteria. Starting from a scalar-tensor framework, we define the relevant swampland quantities in the canonically normalized Einstein frame and relate them to Solar System, Lunar Laser Ranging, equivalence principle, and atomic clock bounds. These probes do not constrain the scalar velocity by itself but rather products of the scalar motion with microscopic couplings to matter, gravity and atomic parameters. For coupling directions that are visible to local experiments, the scalar is driven into an ultra slow present regime and this leads to severely restricting the possibility of realizing an $\mathcal{O}(1)$ de Sitter gradient through unscreened visible sector couplings alone. The refined de Sitter alternative remains viable only in restricted regions of parameter space, such as near a hilltop or under tuned dynamical evolution.