Baby universes in 2d and 4d theories of quantum gravity

A bstract The validity of the Coleman mechanism, which automatically tunes fundamental constants, is examined in two-dimensional and four-dimensional quantum gravity theories. First, we consider Euclidean on orientable closed manifolds coupled to conformal matter central charge c ≤ 1. proper time Hamiltonian this system known be written as a field theory noncritical strings, can also viewed third quantization two dimensions. By directly counting number random surfaces with various topologies, find that contribution baby universes too small realize mechanism. Next, Lorentzian gravity. Based difference between creation mother universe from nothing annihilation into nothing, introduce non-Hermitian effective for multiverse. We show Coleman’s idea satisfied model cosmological constant tuned nearly zero. Potential implications phenomenology are discussed.