Dynamic Scalar Field Theory (DSFT): A Self-Consistent Scalar–Tensor Framework for Cosmic Expansion and Structure Formation

We present the definitive formulation of the Dynamic Scalar Field Theory (DSFT), a conserva- tive scalar–tensor framework in which a single dynamical scalar field drives cosmic expansion and influences structure formation while remaining fully consistent with General Relativity, energy– momentum conservation, and all current local and cosmological constraints. All phenomenolog- ical inconsistencies present in earlier versions of DSFT are corrected. The theory is confronted with data from Planck, DESI, SH0ES, and weak-lensing observations, including recent JWST mass maps, showing full consistency at the background and linear perturbation levels. Distinct, falsifiable predictions for upcoming surveys such as Euclid, Roman, CMB-S4, and LISA are derived.