Urs Schreiber
Shared publiclyYesterday 6:36 PM
Starobinsky Inflation favors Supergravity, or at least that is suggested by the analysis of Dalianis-Farakos that just appeared [1].
As amplified in previous messages [2], experimental observation shows unambiguously that the early universe underwent an inflationary period of the kind originally proposed by Starobinsky [2].
This kind of inflation -- Starobinsky inflation -- starts at much lower energy than for instance the "chaotic inflation" that has received much press, but is ruled out by the reproducible experimental data. As a consequence, for the Starobinsky model in pure gravity to match observation, it needs to start the inflationary process form an initial homogeneous patch of spacetime of some size above the Planck scale.
Assuming ordinary gravity, one finds that this initial homogeneous patch has to have diameter of the order of magnitude of a thousand Planck lengths, see equation (68) in [1].
While insanely small compared to human scales, this is rather large in the quantum gravity regime, where fluctuations have no reason to be suppressed across a few Planck lengths. So this is a theoretical puzzle. Ironically, it is precisely the large-scale homogeneity of the observable universe which inflationary models are designed to explain, but so while Starobinsky inflation in plain gravity fits the observed homogeneous universe best among all models... it leaves unexplained the very last three orders of magnitude of homogeneity.
So Dalianis and Farakos go ahead and check what happens to this prediction when instead the Starobinsky model is implemented in supergravity. They find: in this case the initial homogenous patch reduces to the order of just ten Planck length. This is equation (72) in [1]. That's a much more plausible value.
[1] http://ncatlab.org/nlab/show/Starobinsky+model+of+cosmic+inflation#DalianisFarakos15
[2] https://plus.google.com/108081058828040288656/posts/D7nifMm7Sck
https://plus.google.com/+UrsSchreiber/posts/cshPAumooKo
[3] http://ncatlab.org/nlab/show/Starobinsky+model+of+cosmic+inflation
As amplified in previous messages [2], experimental observation shows unambiguously that the early universe underwent an inflationary period of the kind originally proposed by Starobinsky [2].
This kind of inflation -- Starobinsky inflation -- starts at much lower energy than for instance the "chaotic inflation" that has received much press, but is ruled out by the reproducible experimental data. As a consequence, for the Starobinsky model in pure gravity to match observation, it needs to start the inflationary process form an initial homogeneous patch of spacetime of some size above the Planck scale.
Assuming ordinary gravity, one finds that this initial homogeneous patch has to have diameter of the order of magnitude of a thousand Planck lengths, see equation (68) in [1].
While insanely small compared to human scales, this is rather large in the quantum gravity regime, where fluctuations have no reason to be suppressed across a few Planck lengths. So this is a theoretical puzzle. Ironically, it is precisely the large-scale homogeneity of the observable universe which inflationary models are designed to explain, but so while Starobinsky inflation in plain gravity fits the observed homogeneous universe best among all models... it leaves unexplained the very last three orders of magnitude of homogeneity.
So Dalianis and Farakos go ahead and check what happens to this prediction when instead the Starobinsky model is implemented in supergravity. They find: in this case the initial homogenous patch reduces to the order of just ten Planck length. This is equation (72) in [1]. That's a much more plausible value.
[1] http://ncatlab.org/nlab/show/Starobinsky+model+of+cosmic+inflation#DalianisFarakos15
[2] https://plus.google.com/108081058828040288656/posts/D7nifMm7Sck
https://plus.google.com/+UrsSchreiber/posts/cshPAumooKo
[3] http://ncatlab.org/nlab/show/Starobinsky+model+of+cosmic+inflation
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