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Frank Wilczek's talk is up!

by marcus
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Jul4-11, 06:08 PM
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In the interesting section from 40% to 70% across the timebar, about Inflationary Axion Cosmology, there was one point of definition where I thought I understood something different from Mitchell. In general Mitchell's summary was excellent and helped me see what was going on in one of the graphs:
Quote Quote by mitchell porter View Post
...the very densely illustrated graph with temperature, gas density, and virial velocity as coordinates, and with a yellow star marking a small parametric sweet spot which corresponds to our galaxy.

I believe the points on that graph correspond to populations of gas clouds in the early universe, before galactic formation, and the colored-in regions tell us about what happens to those gas clouds. Some just become black holes, some apparently become too crowded with stars for stable planetary systems to exist ("too close encounters"), etc. And then there were two thin regions of parameter space labeled "halo formation" and "halo destruction". Those would be dark matter halos in the gas clouds. I think dark matter is supposed to seed galactic formation. So the yellow star marks a point where the dark matter halo forms, and where the gas cloud also cools enough for planets to form.

Standard cosmology is characterized by about eleven parameters (dark matter density, total neutrino masses, etc). So this graph must be showing us the fate of those gas clouds with the cosmological parameters tuned to their observed values. Then, in the "inflationary axion cosmology" where the Peccei-Quinn transition occurs after inflation, so you can have different regions in the multiverse (or even in the same inflationary region??) starting with different values of theta_0, the ratio of dark matter density to baryon density can also vary, and that's where Wilczek suggests that anthropic finetuning is at work, leading to his second, much simpler graph, showing a probability distribution for "dark matter per photon" densities that is peaked near the actual value.
Mitchell the way you describe Infl. Axion Cosm. (IAC) inflation occurs first, and then PQ. Maybe the distinction does not matter but I thought he said that corresponded to an earlier view of Axion Cosmo. and that what he meant by IAC was the case where PQ transition comes first (fixing a dark matter ratio in a certain region) and then inflation expands that region so that abundance prevails throughout the whole apparent universe.

Quote Quote by marcus View Post
I agree completely with the helpful summary in your first two paragraphs. Thanks! I don;t agree (or don't understand) your "occurs after", however. You may simply have accidentally misspoken. I think if you drag the time button to almost exactly 50% along the timebar you see him defining the "inflationary axion cosmology" oppositely to what you say here. He at first describes what has been "default" axion cosmology = if no inflation occurs after PQ.

Then he shifts gears and he has a slide that gives the new heading "Inflationary axion cosmology" and the following slide says:
"If inflation occurs after the PQ transition, things are very different... so we shouldn't average..."

Then by contrast you have a multiverse picture with different universe-sized regions each with a different (randomly determined--i.e. environmental) dark matter density.

By this time we are about 55% along the timebar.

The dark matter density is crucial (as you say) to how structure formation is going to play out. So some of these universe-sized regions have good structure formation and others do not. Might have too much or too little condensation.

That is where the overpacked graphs/figures come in, including the one you mentioned. The yellow star is, I guess where we are in that kind of "phase diagram". Max Tegmark leans towards "warm" graphics, it seems. Several times Wilczek seemed to be balking at the design style of his own graphics.
My take on this is that it may be just a verbal slip analogous to forgetting the minus sign in an equation. But I want to be sure because I may have misunderstood something in what either you or Wilczek said.

Obviously he has a paper in the works with Max Tegmark, and it will (I would guess) be coming out quite soon.

The interesting thing is that it PROVIDES A TESTABLE ALTERNATIVE TO THE LIGHTEST SUPERPARTNER hypothesis about the composition of dark matter.
He points to ways to test it.

I think that a scientific alternative hypothesis deserves respect, if it is testable, whether it eventually proves right or wrong. I don't want to bet on stuff like this, but want to honor it as extremely interesting. And he describes approaches to testing starting around 75% along the timebar.
mitchell porter
Jul4-11, 11:19 PM
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You're right Marcus, I was confused (and still am) about how it works, but evidently Wilczek requires that some inflation occurs after the PQ transition. But note that inflation can be occurring before the transition as well! In that case, the PQ transition occurs during inflation, rather than before it. The important part is that regions with the various nonzero values of theta_0 which arise after the PQ transition get blown up to astronomical scales.

In terms of part 2 of this review paper, I think Wilczek must be talking about Case 1, "inflation occurs with reheat temperature smaller than T_PQ [temperature at which PQ transition occurs], and the axion field is homogenized over enormous distances". But it's all a little complicated - there are thermal axions and cold axions; the axion gets its mass at the later transition, the QCD transition; the axion field even mixes with QCD meson fields! And then there are the extra twists that smoit mentions.
Jul9-11, 12:21 PM
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Mitchell, What Wilczek had to say about axions was certainly interesting. I agree with you that it got a bit intricate at places. At least he was explicit and clear about ways to test---especially to falsify, but also as he said potentially to "truthify". I liked it that the theoretical proposals were geared to observation---he stressed that what he was bringing forward was timely, in that sense.

I want to stress that the topic of the first 40% of his talk was "quantitative unification" (abbreviate Q.U.?). This is a three-way unification program (he mentioned the goal of "one material and one force" instead of 6 materials and three forces.) It leaves gravity for later. He argues that the Standard Model is begging for this kind of threeway unification and that the means are now at hand.

He made the point that the various proposals for Q.U. which he didn't have time to list in detail--I recall he mentioned SU(5) and SO(10)--- were timely given the LHC and expected/current cosmology observations---I noticed he repeatedly linked HEP and cosmology.

I was reminded in this connection of a recent Ohwilleke post, which I think raises some of what Wilczek would have included among the various "truthworthy" Q.U. proposals he referred to. Proposals that are "plausible and accessible" (his criterion for appropriate theory.)

In case it can help fill in Wilczek's picture of Q.U., here is Ohwilleke's post from yesterday:
I've been really impressed with the progress that can be made within the Standard Model with a quite minor extension to include four rather than three generations of Standard Model fermions, something that makes possible something very close to unificiation without elaborate and undiscovered SUSY particles or extra dimensions within existing experimental boundaries using nothing more elaborate than an SU(5) framework.

It is one of the most straight foward ways to explain excess CP violation where it is observed and also comports with evidence from the MINOS conference by two different methodologies supporting the existing of more than three generations of neutrinos. P.Q. Hung has made this point in a number of articles among the earliest of which is this one: entitled "Minimal SU(5) Resuscitated by Long-Lived Quarks and Leptons." In this scenario: "SU(3)xSU(2)xU(1) gauge couplings converge to a common point of approximately 3.5x10^{15} GeV (corresponding to a proton lifetime of approximately 10^{34 plus/minus 1} years)." Updates to this original insight in this 1997 paper by Hung have been made by Hung and others to reflect theoretical refinements and new experimental data at least as recently as 2011 in this paper:

An example of how this framework could explain excess CP violation in B and kaon decay is found at

Along the same lines, a five generation model could explain neutrino mass in a satisfactory way.

I am also impressed with the prospects for finding links between the CKM and PMNS mixing matrixes and the masses of the fermions (perhaps via relationships between the square roots of these masses), that could give us better insights into the fundamentals at work in both of these constants, as explored, for example, in this doctoral dissertation:

For my convenience in checking these out, I changed some links to get abstracts rather than PDFs.
Jul13-11, 08:52 PM
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Marcus, thanks for the post. It is a super interesting talk.
Jul14-11, 10:58 PM
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You are most welcome! I think it's a great talk and am delighted when others find it so as well. The conference website has added some more links, including one to the slides PDF:

It used to be we only had the video, so you had to pause the video to make notes by hand. Now you can print out the slides PDF and don't need to make notes, or copy and paste from selected slides.

In case anyone hasn't watched it the streaming video of Wilczek's talk is here:

Unusualname posted this link for downloading the video file, if anyone wants to keep a copy.

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