A Minimal EFT Null Test of ΛCDM: Brane-Stability-Inspired Closure

This preprint presents a minimal Effective Field Theory (EFT) framework for investigating brane stability within the standard ΛCDM cosmological model. The proposed approach is intended as a phenomenological and testable extension rather than a replacement of ΛCDM. The framework explores stability conditions, perturbative behavior, and consistency requirements for brane-inspired cosmological scenarios while maintaining compatibility with the established background cosmology. The manuscript discusses the theoretical motivation, outlines the EFT assumptions, and examines potential implications for late-time cosmology and structure formation. The work is offered as a preliminary contribution intended to stimulate discussion, critical evaluation, and further investigation.