Continuous Cosmic Reemergence through a Longitudinal Boundary State: A Conditional Extension of the ΛCDM Model

In ΛCDM, expansion asymptotically approaches a de Sitter regime (w_eff → −1; Ḣ→ 0) and continues even if acceleration later ceases. This conditional extension of general relativity, FLRW geometry and the Standard Model, without modified gravity or global contraction, asks whether a Universe without a beginning, in the causal sense allowed by the Borde–Guth–Vilenkin theorem, is possible. Observed matter predominance and the absence of annihilation signals motivate conjugate sectors separated by an interface of higher vacuum energy, described by a conjugation-odd field φ and a slowly relaxing field χ. Boundaries driven by Δε consume the interface; relaxation of χ ends acceleration and removes it, permitting matter–antimatter overlap in a decelerating phase under a stated condition. Annihilation and black-hole evaporation approach complete conversion of rest mass; expansion redshifts and dilutes radiation, reducing access to selected transverse channels while preserving three-dimensional geometry. The last conjugate pair is joined by a longitudinal configuration of energy λL; its turnaround defines boundary state BX, with C_β= E_exc+ E_field∥+ DE∥. Its BM description, a continuous collective excitation, is reached at λℓ_c ≃ m_min c². Macroscopic stationarity is instantaneous; microstates are preserved. Symmetric precursor sectors meet centrally in BM; progressive neutralization releases the longitudinal energy at the zero of φ. For η ≳ 0.33 M_Pl the core inflates topologically, forming the interface and both sectors with opposite baryon asymmetries, then standard cosmology. Forming this core is a declared postulate. Local covariant conservation, pressure–volume work and ΔS_gen ≥ 0 hold throughout, without entropy reset.