Asymptotic Safety-30 Years After http://pirsa.org/podcast/C09025 Science 2012 http://blogs.law.harvard.edu/tech/rss en-ca Thu, 09 Feb 2012 04:42:36 -0500 sbradwell@perimeterinstitute.ca Thu, 09 Feb 2012 04:42:36 -0500 G 180 pirsa-admin@perimeterinstitute.ca Steve Bradwell's - Podcast Generator Steven Weinberg http://streamer.perimeterinstitute.ca/mp3/b63e0b3e-c3d3-48b5-bca0-042a4e851f57.mp3 Science http://streamer.perimeterinstitute.ca/mp3/b63e0b3e-c3d3-48b5-bca0-042a4e851f57.mp3 Thu, 05 Nov 2009 09:30:00 -0500 Martin Reuter http://streamer.perimeterinstitute.ca/mp3/1eb3324b-2c64-4ffa-8062-d2c7f7b94c35.mp3 Science http://streamer.perimeterinstitute.ca/mp3/1eb3324b-2c64-4ffa-8062-d2c7f7b94c35.mp3 Thu, 05 Nov 2009 11:00:00 -0500 I shall review on field theory examples, the meaning of the concept of asymptotic safety in the context of low energy effective field theories. Jean Zinn-Justin http://streamer.perimeterinstitute.ca/mp3/9c3ef405-0293-493d-8d19-71d0c26d2100.mp3 Science http://streamer.perimeterinstitute.ca/mp3/9c3ef405-0293-493d-8d19-71d0c26d2100.mp3 Thu, 05 Nov 2009 14:00:00 -0500 Holger Gies http://streamer.perimeterinstitute.ca/mp3/a5660c6c-fd71-41d2-9c73-5d12442ff263.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a5660c6c-fd71-41d2-9c73-5d12442ff263.mp3 Thu, 05 Nov 2009 15:00:00 -0500 In Weinberg’s asymptotic safety approach to quantum gravity, one has a finite dimensional critical surface for a UV stable fixed point to generate a theory of quantum gravity with a finite number of physical parameters. The task is to demonstrate how this fixed point behavior actually arises. We argue that, in a recently formulated extension of Feynman’s original formulation of the theory, which we have called resummed quantum gravity, we recover this fixed-point UV behavior from an exact re-arrangement of the respective perturbative series. We argue that the results we obtain are consistent both with the exact field space Wilsonian renormalization group results of Reuter and Bonanno and with recent Hopf-algebraic Dyson-Schwinger renormalization theory results of Kreimer. We calculate the first "first principles" predictions of the respective dimensionless gravitational and cosmological constants and argue that they support the Planck scale cosmology advocated by Bonanno and Reuter as well. Comments on the prospects for actually predicting the currently observed value of the cosmological constant are also given. B.F.L. Ward http://streamer.perimeterinstitute.ca/mp3/bb26c413-245d-48aa-ab2d-13eff815c116.mp3 Science http://streamer.perimeterinstitute.ca/mp3/bb26c413-245d-48aa-ab2d-13eff815c116.mp3 Thu, 05 Nov 2009 16:30:00 -0500 Lee Smolin http://streamer.perimeterinstitute.ca/mp3/d2b3cdd6-1f81-4ff9-a6fd-dc9208f4336f.mp3 Science http://streamer.perimeterinstitute.ca/mp3/d2b3cdd6-1f81-4ff9-a6fd-dc9208f4336f.mp3 Fri, 06 Nov 2009 09:30:00 -0500 Renate Loll http://streamer.perimeterinstitute.ca/mp3/909ec3b1-20ee-440b-819e-92410d48faf7.mp3 Science http://streamer.perimeterinstitute.ca/mp3/909ec3b1-20ee-440b-819e-92410d48faf7.mp3 Fri, 06 Nov 2009 11:00:00 -0500 The fixed point structure of the renormalization flow in Einstein gravity and higher derivative gravity is investigated in terms of the background effective action. Using a covariant operator cutoff that keeps track of powerlike divergences and the transversal-traceless decomposition a construction is proposed that renders the {it regularized} one-loop effective action gauge independent on-shell. In combination with a `Wilsonian' matching condition nontrivial strictly positive fixed points for the dimensionless Newton constant $g$ and the cosmological constant $lambda$ can then be identified already in one loop perturbation theory. The renormalization flow is asymptotically safe with respect to the nontrivial fixed points in both cases. In Einstein gravity a residual gauge dependence of the fixed points is unavoidable while in higher derivative gravity both the fixed point and the flow equations are universal. Along this flow spectral positivity of the Hessians can be satisfied, evading the traditional positivity problems. Dependence on $O(10)$ initial data is erased to accuracy $10^{-5}$ after $O(10)$ units of the renormalization mass scale and the flow settles on a $lambda(g)$ orbit. Max Niedermaier http://streamer.perimeterinstitute.ca/mp3/892ef7be-373b-4659-81d9-6df0e672a520.mp3 Science http://streamer.perimeterinstitute.ca/mp3/892ef7be-373b-4659-81d9-6df0e672a520.mp3 Fri, 06 Nov 2009 14:00:00 -0500 Frank Saueressig http://streamer.perimeterinstitute.ca/mp3/d11d0dfe-6beb-41a0-aea8-7798ce1a5e57.mp3 Science http://streamer.perimeterinstitute.ca/mp3/d11d0dfe-6beb-41a0-aea8-7798ce1a5e57.mp3 Fri, 06 Nov 2009 15:00:00 -0500 Elisa Manrique http://streamer.perimeterinstitute.ca/mp3/782dd334-a812-4149-9d34-83118426749d.mp3 Science http://streamer.perimeterinstitute.ca/mp3/782dd334-a812-4149-9d34-83118426749d.mp3 Fri, 06 Nov 2009 16:30:00 -0500 Christoph Rahmede http://streamer.perimeterinstitute.ca/mp3/daf9e52f-f09c-4d96-b314-1b7747ae61c7.mp3 Science http://streamer.perimeterinstitute.ca/mp3/daf9e52f-f09c-4d96-b314-1b7747ae61c7.mp3 Fri, 06 Nov 2009 17:00:00 -0500 Omar Zanusso http://streamer.perimeterinstitute.ca/mp3/404fc409-5fa4-4ea8-84c0-985856860526.mp3 Science http://streamer.perimeterinstitute.ca/mp3/404fc409-5fa4-4ea8-84c0-985856860526.mp3 Fri, 06 Nov 2009 17:30:00 -0500 Arkady Tseytlin http://streamer.perimeterinstitute.ca/mp3/f1810c9c-aeb2-4d38-ada8-29d11e55911f.mp3 Science http://streamer.perimeterinstitute.ca/mp3/f1810c9c-aeb2-4d38-ada8-29d11e55911f.mp3 Sat, 07 Nov 2009 09:30:00 -0500 Vincent Rivasseau http://streamer.perimeterinstitute.ca/mp3/6b3105c8-9347-4214-97df-86e4a2284d87.mp3 Science http://streamer.perimeterinstitute.ca/mp3/6b3105c8-9347-4214-97df-86e4a2284d87.mp3 Sat, 07 Nov 2009 11:00:00 -0500 Alfio Bonanno http://streamer.perimeterinstitute.ca/mp3/98601e6f-5dd6-4dd6-86d2-3dd43ebd183a.mp3 Science http://streamer.perimeterinstitute.ca/mp3/98601e6f-5dd6-4dd6-86d2-3dd43ebd183a.mp3 Sat, 07 Nov 2009 14:00:00 -0500 I will present recent results through four loops demonstrating that the maximally supersymmetric (N=8) generalization of gravity is surprisingly well behaved in the ultraviolet as a result of unexpected cancellations between contributing terms. These cancellations first manifest at one loop in the form of the "no-triangle property," with all-loop order implications through unitarity. I will conclude by discussing similar novel cancelations identified in pure Einstein gravity, at one loop, which suggest a possible explanation for the unexpectedly tame high energy behavior of N=8 supergravity beyond the limited UV protection of supersymmetry. John Joseph M. Carrasco http://streamer.perimeterinstitute.ca/mp3/94d17692-74ee-4a52-9523-fee24c239e8c.mp3 Science http://streamer.perimeterinstitute.ca/mp3/94d17692-74ee-4a52-9523-fee24c239e8c.mp3 Sat, 07 Nov 2009 15:00:00 -0500 Gian Paolo Vacca http://streamer.perimeterinstitute.ca/mp3/f1405a14-45e4-4ff1-880f-88992c07317b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/f1405a14-45e4-4ff1-880f-88992c07317b.mp3 Sat, 07 Nov 2009 16:30:00 -0500 Michael Scherer http://streamer.perimeterinstitute.ca/mp3/afe917b9-7ad2-43d1-9f14-d0249d992e91.mp3 Science http://streamer.perimeterinstitute.ca/mp3/afe917b9-7ad2-43d1-9f14-d0249d992e91.mp3 Sat, 07 Nov 2009 17:00:00 -0500 Jan Ambjorn http://streamer.perimeterinstitute.ca/mp3/fdd33378-a410-40a4-9a41-11bb7dc685e1.mp3 Science http://streamer.perimeterinstitute.ca/mp3/fdd33378-a410-40a4-9a41-11bb7dc685e1.mp3 Sun, 08 Nov 2009 09:30:00 -0500 Daniel Litim http://streamer.perimeterinstitute.ca/mp3/868bbc2b-f5f4-443a-9c3a-d1f561e53ad6.mp3 Science http://streamer.perimeterinstitute.ca/mp3/868bbc2b-f5f4-443a-9c3a-d1f561e53ad6.mp3 Sun, 08 Nov 2009 11:00:00 -0500