# Videos for Asymptotic Safety conference are online

1. Nov 5, 2009

### marcus

Last edited by a moderator: May 4, 2017
2. Nov 5, 2009

### MTd2

What is your opinion on Ward ressumation?

3. Nov 5, 2009

### marcus

I have not watched Ward's talk yet. I looked through his slides and they seemed quite interesting. I expect they will mount the "flash" version (better for my computer) and I am looking forward to watching his talk when that version becomes available.

Last edited: Nov 5, 2009
4. Nov 6, 2009

### marcus

I was now able to watch the Ward talk, and curiously enough I found it the most interesting and exciting presentation so far!

Also Ward has good communication skills, good slides, clear language and pacing. (not too fast or too slow). Also it could interest me more because I was not familiar already with his work-----what Weinberg said and what Reuter said was more of a repetition for me.

They still have not mounted the flash version of Ward's talk but one can use the MP3 audio in conjunction with the Windows version and make it work with a little adjustment.
================

Soon we should have talk videos by Lee Smolin, Renate Loll, Frank Saueressig, and Christophe Rahmede. Saueressig is a young co-author of Reuter who was postdoc at Utrecht until recently and has worked with members of Loll's group. Rahmede will be presenting joint work with Percacci. He was postdoc at Trieste (Italy's Inst. Advanced Studies) and now joined Litim's group at Sussex.

In a sense AsymSafe succeeds or fails depending on the energy of these young people: Holger Gies, Saueressig, Rahmede. And one function of this conference is to allow anybody (and us) to gauge the talent and energy of the newcomers that we would not normally know of or have seen.

BTW I think the guy who introduced Weinberg's talk was the chairman/organizer Roberto Percacci. Did you get any impression of him?

The collection of AsymSafe conference talks is here:
http://pirsa.org/C09025
So we can check that sometime later today and see if today's talks have been posted.

THE NEXT BATCH IS ON LINE.
Smolin
http://pirsa.org/09110044/
Loll
http://pirsa.org/09110045/
Niedermayer
http://pirsa.org/09110046/
Saueressig
http://pirsa.org/09110047/

Last edited: Nov 6, 2009
5. Nov 6, 2009

### MTd2

Looking at Ward's citation summary,
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+EA+WARD,+B+F+L&FORMAT=wwwcitesummary&SEQUENCE= [Broken]
You can see that he is at least a very accomplished physicist. And looking at his publication list you can see that he is an excellent specialist in the phenomenology of high energy scattering. So, what also really surprises me why he didn't make his work known to any of the people in the conference. I mean, it would be really a piece of cake to get people in the right field to know his ideas.

I don't know if you'll agree with me, but I noticed that Weinberg was taking notes intensively during his presentation, and that other people were asking questions in disbelief, like what he's saying was way too good to be true.

Last edited by a moderator: May 4, 2017
6. Nov 6, 2009

### marcus

I certainly agree with you. "Too good to be true" was my instinctive reaction. But in cases like this I refrain from trusting my intuition. I have to discount my gut feelings in this case because I just haven't enough knowledge or experience with what he is talking about.

Another thing is my impression that Baylor University is not a first-rank elite place. It is not prominent like Harvard, Princeton, UC Berkeley. I think Ben Ward is Chairman of the Physics Department at Baylor. But what do I know?

Right now on a provisional basis I give him full credence. Nothing I saw or heard from the audience undermines this.
In the end we will see if he can get some of the young people, the PhD students and postdocs, to go along with him. It's all that matters. These are early days for AsymSafe and a lot of different lines will be explored.

=====================

I just watched Lee Smolin's talk. Some provocative and exciting ideas. Something that impressed me was the extent to which he is building bridges to Horava QG. Horava was in the audience (he is attending AsymSafe) and Lee made a dozen or so friendly references to Peter's "anisotropic scaling" approach. He used BOTH LQG AND HORAVA QG interchangeably as examples to illustrate many of his points.

Lee's talk was not centered on any one specialized QG approach but was giving plausibility arguments, suggestive reasoning that applied more generally across the board.
He drew connections like:

AsymSafe---Reduced spacetime dimensionality---Horava gravity---DSR (more specifically not the quantum-group type DSR but the idea of energy-dependent metrics.)

Last edited: Nov 6, 2009
7. Nov 6, 2009

### MTd2

Most of his articles, including the most cited, were published while staying on Stanford. It seems he just moved to Baylor recently. Maybe he wanted a quieter place? It seems he is not very young according to that video.

So, you mean that Stanford is not a good place for a HEP-Phenomenologist to work at, even during the early 80's. Hmm, sounds counter intuitive.

Anyway, I always wanted to adopt a black child one day and Id like him to have one more nice role model, hmm. Maybe I am being racist? Oh well.

8. Nov 6, 2009

### marcus

Hmmm. No I did not mean that! That would indeed be counter intuitive. Stanford in the 80s sounds excellent to me. I did not look back to see where Ward was earlier, before Baylor. He impressed as being very sharp, in his talk.

9. Nov 7, 2009

### MTd2

The reamaining of yesteradays videos and some of today's are up.

Yesterday

http://pirsa.org/09110123/

Elisa Manrique

http://pirsa.org/09110124/

Christoph Rahmede

Today

http://pirsa.org/09110127/

Omar Zanusso

http://pirsa.org/09110048/

http://pirsa.org/09110049/

Vincent Rivasseau

I am really curious to see Vicent's talks.

BTW, Marcus, do not forget to see tomorrow's talk on Horava gravity, although I am extremely disappointed to see that the people who figure out the bugs of the theory were in fact dark matter were not invited to the talk.

10. Nov 7, 2009

### MTd2

11. Nov 7, 2009

### marcus

For me the talk by Vincent Rivasseau must be the most surprising and innovative one of the whole conference. The only words that come to mind, on first looking at the PDF slides, are superlatives. He brings Group Field Theory into the AsymSafe picture and in particular draws connections to the work of the authors he calls EPRLS-FK (Engle, Pereira, Rovelli, Livine, Speziale, Freidel, Krasnov.)

Of particular interest are his slides 179-182
And then his slides 183-191.
And the conclusions at the end.

Maybe we should summarize.

http://pirsa.org/09110049/
My computer is not yet able to get the audio or the video, but the PDF for the slides is:
http://pirsa.org/pdf/files/6b3105c8-9347-4214-97df-86e4a2284d87.pdf [Broken]

Last edited by a moderator: May 4, 2017
12. Nov 7, 2009

### marcus

What he does in this talk makes a bridge between Asymptotic Safety and Loop/Foam QG. He opens with a discussion of GFT. Here is slide #155
==quote 155==
Group Field Theory

Group field theory (Boulatov, 1992) lies at the crossroads between loop quantum gravity and simplicial quantum gravity. It generalizes matrix field theory and is also an attempt to sum both over discretized metric and topology of space-time.

*The information about the metric of a manifold is encoded in the hologomies along closed curves. Therefore the fields live on a group GD (typically G = SO(D-1, 1)). They are G-gauge invariant.

*The simplest group field theories are topological. The interaction glues D+1
(D-1)-dimensional simplexes into a D dimensional simplex. Hence the theory has phiD+1-type interaction. Feynman amplitudes correspond to BF theory, and they coincide with the spin foams of loop quantum gravity.
==endquote==

==quote 164==

Group field theory is non-local and its renormalization is again expected to involve
*A new scale decomposition (with a half-direction, hence uv/ir mixing?),
*A new locality principle ("triangularity") that should hold only for special classes of graphs,
*A new power counting.

Some non-topological theories of this type could be renormalizable in dimension 4 and form a consistent field theory of quantum gravity.
==endquote==

He cites Freidel-Gurau-Oriti 0905.3772 and discusses their results in 3D GFT, which he refers to as a "warm-up" exercise.
Then he refers to some work on GFT scaling bounds. Magnen-Noui-Rivasseau-Smerlak 0906.5477. This leads to a scale parameter appropriate to simplicial or graph-based formalism such as GFT and Loop/Foam. A scale parameter along which the coupling constants can, in effect, run. This is important, to do renormalization flow one must have an appropriate concept of the scale. If it is not some naive distance measure from some pre-established metric, then maybe it can be a measure of the complexity of the detail that one can see with the microscope. A kind of "fine versus coarse" measure. ( ! )

Then he moves on, and suddenly he is at slide #182

==quote 182==

EPRLS-FK Models

The BF theory in four dimensions is not general relativity. The difference is expressed through Plebanski constraints. The problem is in a sense to relax the exact gluing of D-1 simplexes in order to allow for the propagating degrees of freedom of 4D gravity to be reflected in an appropriate way in the group field theory propagator.

Works by Engle-Pereira-Rovelli, Freidel and Krasnov, Livine and Speziale, led in 2007 to a model which implements better the Plebanski constraints.

In group field theory language the vertex of this model is made of two 15j symbols like in BF theory. But the Plebanski constraints add two special intertwiners f in the middle of each propagator. There are also natural normalizing factors dj+ and dj- for each face.

At large spins the vertex plus its half propagators obeys the desired semi-classical asymptotic limit (Conrady-Freidel, Barrett et al., 2009).
==endquote==

==quote 191==

Asymptotic safety in GFT?

The elements responsible for asymptotic safety of the Grosse-Wulkenhaar model are also present in the EPRLS-FK model:

*The model seems to have the right power counting (Pereira-Rovelli-Speziale 2009)
*It is non-local in group space.
*There is an auxiliary parameter, the Immirzi parameter gamma with interesting enhanced symmetry at gamma = 1.

Therefore we might hope for asymptotic safety in some model of this type.
It is unclear how such a possible asymptotic safety would be related to the fixed points seen in the Functional Renormalization Group (FRG) studies.
==endquote==

Last edited: Nov 7, 2009
13. Nov 7, 2009

### MTd2

I have yet to see Vincents talk. But it must be something really amazing considering that Wards talk claimed that GR is renormalizable. I guess I should ask ward how he fits his results to the flow in the (^,G) space.

I am also curious to see Carrascos talk. N=8 supergravity is by far the simplest interacting QFT in 4d ( http://arxiv.org/abs/0808.1446). I wonder how he will try to connect that to GR.

14. Nov 7, 2009

### atyy

Marcus, just saw your comments on the Zurueck thread. Rivasseau's work, also Freidel, Gurau and Oriti's, is actually one of the reasons I think some form of spin foam gravity will violate Lorentz invariance, because I don't think GFT renormalization will be like AS renormalization, and I assume Lorentz invariance will not be violated in AS (Smolin's suggestions notwithstanding).

My caricature of the two LQG camps are :
(i) fundamental smoothness by taking a continuum limit before the semi/classical limit - with fundamental smoothness, there is at least hope for Lorentz invariance
(ii) fundamental discreteness with smooth spacetime emerging only at large scales - with fundamental discreteness, Lorentz invariance will probably be violated.

15. Nov 7, 2009

### marcus

Have you looked at this September 2009 paper of Rivasseau?

http://arxiv.org/abs/0906.5477
Scaling behaviour of three-dimensional group field theory
Jacques Magnen (CPHT), Karim Noui (LMPT), Vincent Rivasseau (LPT), Matteo Smerlak (CPT)

Great paper, I think. It covers a lot of what he said in his talk.
I will try to reply to your post later, hopefully soon. Busy with something now.

16. Nov 7, 2009

### atyy

Yes, I like the direction in that paper very much. Look out also for Freidel, Gurau and Oriti; and Tanasa.

Possibly the other direction which actually is also very nice, but more conservative, is Bahr and Dittrich, and maybe Krasnov, which I think are more related to AS.

17. Nov 7, 2009

### marcus

Your post reminded me of a sequence of twelve slides by Rovelli, which is the middle segment of this batch:
http://relativity.phys.lsu.edu/ilqgs/panel050509.pdf
The sequence starts at the 8th slide in the batch and goes to around slide #20

You scroll past the first 7 slides, and there is a new title "Getting physics from quantum gravity". And a new numbering starts, so the 9th slide in the batch is numbered "2".
Have you had a look at those 12 slides?

Philosophically he is talking at a fairly sophisticated level. It is a threeway discussion Ashtekar, Rovelli, Freidel. I think the essential message is that there is no difference between smoothness and discreteness. at a fundamental level. Neither concept is meaningful, at fundamental scale. What we are actually talking about is how nature responds to measurements.

Anyway, I'm not sure your "two camps" exist. Or which real people would fit into which of your categories.

For example, could you imagine Rovelli being in your camp (i)? Your camp (i) is defined this way:
"(i) fundamental smoothness by taking a continuum limit before the semi/classical limit - with fundamental smoothness, there is at least hope for Lorentz invariance"

I don't remember ever seeing Rovelli take a continuum limit before a semiclassical limit. Not sure what that means. Could you point to some page of some paper on arxiv, where I could look and see these limits being taken? You could be right! I just can't think of an instance.

On the other hand perhaps you imagine Rovelli in camp (ii). That makes better sense because he has often talked about the LQG having fundamental discreteness. This vision of spacetime discreteness is based on the discrete spectra of the geometric observables---area and volume measurement. You see a lot of discreteness just in those slides I pointed to.
But this does not imply Lorentz violation! So why do you say the following?
"(ii) fundamental discreteness with smooth spacetime emerging only at large scales - with fundamental discreteness, Lorentz invariance will probably be violated."

Maybe this is a disappointment, but it looks to me as if LQG is able to adapt either way, to agree with observation however they turn out, on this issue. It doesn't seem possible to test the theory on this issue, as many people would have liked. Some other means of testing will have to be found. A disappointment, but just how it turns out.

Why do you say probably? I think we just have to wait for the Fermi-LAT observations to tell us if there is some energy-dependence, some dispersion. At this point I would not try to guess nature. I would refrain from declaring probably yes or probably no. However it turns out that nature is, in this regard, will be OK. Theory will adapt. But on what basis can you, Atyy, guess ahead of time?

Last edited: Nov 8, 2009
18. Nov 8, 2009

### atyy

I hadn't seen them before - and I don't understand them.

Maybe smooth/discrete is not fundamental - I've seen it suggested in http://arxiv.org/abs/0909.4221 "the exact physical inner product is obtained by summing over just the discrete geometries; no `continuum limit' is involved" - this is what I meant by that paper indicating that one might eat one's cake and have it. But I don't get the sense that Rovelli's slides were saying the same thing.

19. Nov 8, 2009

### atyy

Yes, I imagine Rovelli here - discrete area spectrum isn't fundamental discreteness in the sense I mean since LQG still has an underlying smooth manifold. The sense I get is Rovelli would like spin foams to tie in completely with LQG - so fundamental smoothness.

There isn't any paper about continuum limit before semiclassical limit, but there are papers about continuum limits of spin foams eg. Noui & Perez http://arxiv.org/abs/gr-qc/0402110 "The Ponzano-Regge model amplitudes are recovered from the Hamiltonian theory and its ‘continuum limit’ in the sense of Zapata [29] built in from the starting point." ie. this paper connects spin foams and LQG in 3D, and I think Rovelli would like to do the same in 4D - which I think is the Kaminski et al program also http://arxiv.org/abs/0909.0939. The semiclassical limit of spin foams seems to be a separate line of work at the moment (Conrady & Freidel, Barrett et al)- will it tie in with the continuum limit line of work (Noui & Perez, Kaminski et al)?

Edit: If the limits commute then there will be no problem tieing work on both sorts of limits together - so that would be possibility (iii).

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20. Nov 8, 2009

### atyy

He says the opposite - he does not know if an asymptotically safe GFT will have anything to do with Asymptotic Safety of metric gravity.