No-boundary prescriptions in Lorentzian quantum cosmology

Understand

We analyse the impact of various boundary conditions on the (minisuperspace) Lorentzian gravitational path integral.

• In particular we assess the implications for the Hartle-Hawking no-boundary wavefunction.
• It was shown recently that when this proposal is defined as a sum over compact metrics, problems arise with the stability of fluctuations.
• These difficulties can be overcome by an especially simple implementation of the no-boundary idea: namely to take the Einstein-Hilbert action at face value while adding no boundary term.