It is shown that the standard no-boundary wave function has a natural expression in terms of a Lorentzian path integral with its contour defined by Picard-Lefschetz theory. The wave function is real, satisfies the Wheeler-DeWitt equation and predicts an ensemble of asymptotically classical, inflationary universes with nearly-Gaussian fluctuations and with a smooth semiclassical origin.

We evaluate the no-boundary path integral exactly in a Bianchi type IX minisuperspace with two scale factors. In this model the no-boundary proposal can be implemented by requiring one scale factor to be zero initially together with a judiciously chosen regularity condition on the momentum conjugate to the second scale factor. Taking into account the nonlinear backreaction of the perturbations we recover the predictions of the original semiclassical no-boundary proposal. In particular we find that large perturbations are strongly damped, consistent with vacuum state wave functions.

Abstract:The unwinding inflation mechanism is studied in a type IIB flux compactification where all moduli are stabilized using flux, non-perturbative effects, and the leading α corrections of the large volume scenario. We consider the backreaction on the geometry due to the presence of anti-D3 branes as well as the backreaction of inflation on the Kähler moduli, and compute the resulting corrections to the slow-roll potential. By taking large flux numbers, we are able to find inflationary epochs where backreaction effects are under control, the inflaton traverses a super-Planckian field range, and the resulting amplitude of scalar perturbations is consistent with observation.

Flat domain walls and spherical black holes are solutions to coupled secondorder ODE's of the Hamiltonian form. Hamilton-Jacobi theory then implies that first-order flow equations always exist (possibly up to isolated submanifolds). If the first-order equations factorise in a specific way, they take a form that has been named fake supersymmetry. We point out that this factorisation is always possible at zero temperature. We therefore propose a less generic definition of fake supersymmetry, which involves the boundary conditions in a non-trivial way, and we analyse its physical relevance. For instance attractor flows are necessarily fake supersymmetric in our restricted sense. To illustrate the definition we provide new analytic solutions for axion-dilaton domain walls with fake superpotentials that were argued not to exist.

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