Microsynaptic Space Fabric (MSF) and Rhombic Field Theory (RFT): A Variational Formulation with a Directional Effective Metric and Null Geodesics

This preprint formulates the macroscopic limit of the Microsynaptic Space Fabric (MSF) approach as a minimal covariant effective model. The conjectured long-wavelength directional order of the underlying microstructure is represented by a continuous field Φμ, coupled to an Einstein–Hilbert gravitational sector and a rank-one disformal optical metric, g̃μν = gμν + λΦμΦν, governing electromagnetic propagation. Defining the electromagnetic action directly on this optical metric preserves U(1) gauge invariance and yields the modified null cone and photon trajectories dynamically in the geometric-optics limit. The resulting rays follow null geodesics of the effective metric, allowing the geodesic ray-tracing and kernel-weighted orientation operators developed within Rhombic Field Theory (RFT) to serve as an explicit observational layer of the MSF model. The construction is presented as a restricted and falsifiable effective-model truncation rather than an operator-complete theory or a completed theory of quantum gravity. It possesses a smooth General Relativity limit, states its causality and Lorentzian-signature conditions explicitly, and identifies the coupled weak-field solution around a static spherical source as the necessary next step toward quantitative light-deflection and Shapiro-delay tests.