Gauge-Gravity by the Ghats Seminar (Season 2)

Speaker: Oliver Janssen (EPFL, Switzerland)

Title: The no-boundary puzzle: a review and a possible resolution

Abstract: We will review the Hartle-Hawking proposal for the wave function of the universe, which is supposed to provide a theoretical prior on cosmological observables. Puzzlingly, although providing a sensible answer for small fluctuations around an inflationary background, when applied to the background itself, it predicts the curvature of the universe to be large, in contrast with observations. The proposal is based on a semiclassical evaluation of the path integral in quantum gravity, employing complexified solutions. We will then review an “allowability” criterion on saddles based on the convergence of fluctuations around them, and apply it to Hartle-Hawking solutions in the contexts of inflation and spatial anisotropy. We argue this provides a way towards solving the large curvature problem and gives a sharp prior on the prevalence of primordial gravitational waves, in agreement with observations.

Meeting link will updated close to the seminar date