On suppression of topological transitions in quantum gravity
  We discuss the effect of dynamical suppression for a special class of topological configurations in cosmology, which occur in Euclidean quantum gravity (EQG) when the latter is viewed as the derivative of the physical theory in the Lorentzian signature spacetime. At the topological level EQG inherits from the Lorentzian theory the arrow of time and incorporates special junction conditions on quantum fields whose quantum fluctuations make the contribution of such topologies vanishing. This effect is more general than the recently suggested conformal mechanism of suppression of vacuum no-boundary instantons in the microcanonical statistical sum of quantum cosmology driven by a conformal field theory (CFT). In contrast to conformal properties of the CFT driven cosmology, this effect is based only on short-distance behavior of local boson fields and Pauli principle for fermions. Application of this effect in the CFT cosmology treated as initial conditions for inflationary Universe suggests the thermal nature of the primordial power spectrum of the CMB anisotropy. This can be responsible for a thermal contribution to the red tilt of this spectrum, additional to its conventional vacuum component. 
A.O.Barvinsky
hep-th gr-qc