Abstract
We argue that the Lorentzian path integral is a better starting point for quantum cosmology than the Euclidean version. In particular, we revisit the minisuperspace calculation of the Feynman path integral for quantum gravity with a positive cosmological constant. Instead of rotating to Euclidean time, we deform the contour of integration over metrics into the complex plane, exploiting PicardLefschetz theory to transform the path integral from a conditionally convergent integral into an absolutely convergent one. We show that this procedure unambiguously determines which semiclassical saddle point solutions are relevant to the quantum mechanical amplitude. Imposing "noboundary" initial conditions, i.e., restricting attention to regular, complex metrics with no initial boundary, we find that the dominant saddle contributes a semiclassical exponential factor which is precisely the {\it inverse} of the famous HartleHawking result.
Original language  English 

Article number  103508 
Pages (fromto)  120 
Number of pages  20 
Journal  Physical Review D 
Volume  95 
Issue number  10 
DOIs  
Publication status  Published  15 May 2017 
Keywords
 hepth
 grqc
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Neil Turok
 School of Physics and Astronomy  Higgs Chair of Theoretical Physics
Person: Academic: Research Active