Irreversible Quantum Cascade of the Vacuum Energy in Pre-Geometric Gravity

We show how the pre-geometric MacDowell–Monsouri gravity inevitably leads to an irreversible quantum cascade mechanism for the vacuum energy density. Such a process is a consequence of the spontaneous symmetry breaking (SSB) SO(1,4)→SO(1,3) dynamics and quantum anomalies. The dynamics are governed by a periodic Higgs potential, which generates a countably infinite sequence of metastable vacua separated by large energy barriers. The multi-vacua structure is direct consequence of a see-saw duality of the θ-term, the vacuum expectation values and the cosmological constant. After the SSB, a discrete spectrum of vacuum energy levels is predicted. As a consequence, starting from an initial high-energy vacuum energy associated to cosmological constant Λ1, the system evolves via sequential quantum tunneling accessing through the landscape of lower minima. In particular, we demonstrate that the transition probability is maximized for the strictly ordered cascade flowing towards the Λ∞=0 attractor. This process is intrinsically time-asymmetric, offering a natural quantum origin for the thermodynamic arrow of time. In this mechanism, the vacuum relaxation acts as a “cosmic clock”, correlating the expansion history with the progressive reduction in the cosmological constant. Our findings suggest that the observed smallness of the vacuum energy today is the result of a dynamical selection effect.