On a Z2-invariant model of gravity

An effective model for pure gravity is investigated, the theory space of which admits a Z2 modular group. The independence of some modular invariant expectation values from the number of Big Bangs enforces a quantization condition on the cosmological constant and the dimension D of the universe. In the quasi-classical limit, Λ = 0. The only possible integer values for D are 4, 2, 1