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We discuss applications of perturbative quantum gravity in the theory of veryearly quantum Universe and quantum cosmology. Consistency of the theoreticalformalism for quantum effects of matter and correspondence with observationalstatus of modern precision cosmology impose stringent bounds on and establishstrong links with high energy particle phenomenology. Within this line ofreasoning we study various aspects of one-loop approximation for thecosmological wave function, review Higgs inflation model intertwining thephysics of electroweak sector of the Standard Model with the characteristics ofthe observable cosmic microwave background and, finally, consider the problemof quantum initial conditions for inflationary Universe. We formulate acosmological quantum state in the form of the microcanonical density matrix --a universal equipartition of eigenstates of the Wheeler-DeWitt equations. Wedemonstrate elimination of the inalienable infrared catastrophe of vanishingcosmological constant for the no-boundary quantum state of the Universe andderive initial conditions for inflation in the form of a special garland-typecosmological instanton -- the saddle point of quantum gravity path integral.Applied to the cosmological model of the Universe with a hidden sector ofnumerous conformally invariant higher spin fields, this setup suggests asolution to the problem of hierarchy between the Planck and the inflationenergy scales and, thus, admits applicability of perturbative semiclassicalexpansion methods.

Nonminimal Higgs Inflation and Initial Conditions in Cosmology