Continuous Cosmic Evolution through Longitudinal Boundary States and Cosmological Reemergence: A Conditional Extension of the ΛCDM Branch

This work presents a conditional phenomenological extension of the expanding cosmological branch described by general relativity and Friedmann–Lemaître–Robertson–Walker geometry. Two conjugate matter- and antimatter-dominated regions are initially separated by a finite dark-sector-only interface. Their boundaries are assumed to advance bilaterally over this interface, removing its exclusively separating role before matter and antimatter overlap and annihilate. Subsequent expansion dilutes the radiation and reduces access to the transverse excitation channels relevant to the proposed boundary regime, while the underlying spatial geometry remains three-dimensional. Two residual conjugate excitations persist at the ends of a preexisting longitudinal field. Reorganization during the approach to the boundary establishes BX and BM as corresponding descriptions of the same critical configuration: separated residual excitations and a continuous collective longitudinal excitation with conjugate sectors in central contact. Their subsequent neutralization transfers energy to radiation and, through suitable couplings, to transverse excitations, allowing a hot three-dimensional regime with standard thermal evolution to remerge. The construction distinguishes local energy conservation from a conditional energy balance for the boundary domain. Its entropy account admits conserved comoving radiation entropy, microscopic longitudinal capacity, and an entropy-neutral boundary correspondence under explicit conditions, while irreversible processes may increase entropy. The proposed macroscopic recurrence requires no entropy reset or global contraction. Its purpose is to formulate this possibility, rather than establish its cosmological realization or provide a complete microscopic derivation.