Causally Separated
Conjugate Universes:Opposite Baryon Asymmetry and Portal-Regulated Annihilation under Multiverse Balance Laws

We formulate a phenomenological model in which a common cosmological seed produces two conjugate universe branches with equal-magnitude and opposite-sign baryon asymmetries. Each branch has an ordinary 3 + 1 dimensional Lorentzian spacetime, one future-directed time orientation, and positive matter-antimatter energy. With a branch label r = ±1, the signed excess is η_B,r = rb, where b > 0. The r = −1 branch is therefore antimatter dominated, not a negative-mass or negative-energy universe. Ordinary annihilation within each branch removes the symmetric baryon-antibaryon population and leaves a residual proportional to |η_B|. Possible inter-branch interaction is encoded by

We distinguish three mutually consistent models: strict separation with Ω = 0; a weak portal with 0 < Ω ≪ 1 and small integrated optical depth; and transient contact for which Ω > 0 only near a bounce or brane-collision event. In a microscopic portal theory, the densities and distance entering this rate must be defined in a common contact or mediator geometry. Annihilation converts positive rest energy into radiation and other products; it does not erase energy, spacetime, or a universe. We incorporate this conversion into an open-subsystem energy ledger, give a nonnegative coarse-grained entropy-production term, and embed the pair in a cyclic genome based on b = |η_B|. The strict model is a consistency construction without direct cross-branch observables. Portal extensions are conditionally testable through baryon depletion, radiation injection, spectral distortions, expansion-history changes, diffuse high-energy backgrounds, and gravitational waves.