Lorentz invariance verified almost to Planck scale?

[ZapperZ]

So whose quantum gravity theory will crash-and-burn if this is correct?

http://physicsworld.com/cws/article/news/40834

Zz.

 

[Bob_for_short]

Everything that is based on a curved space-time.

Vive Logunov's RTG in a flat space time!

 

[dlgoff]

In the article...

He also points out that his group's approach probes just one of a number of possible effects of Lorentz invariance violation, and that extremely precise constraints on this violation have been obtained by studying the possible dependence of light speed on photon polarization from X-rays emitted by the Crab nebula.

I am curious what these studies on the dependence of speed on polarization are/were.

Any references?

Thanks

 

[ZapperZ]

If you have access to Nature advance online publication, you can check the references for yourself:

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature08574.html

Zz.

 

[marcus]

Nice!

Thanks for the link.

 

[marcus]

So whose quantum gravity theory will crash-and-burn if this is correct?

Unfortunately none of the QG theories being currently worked on, as far as I know.
But the result will still be helpful.

 

[MTd2]

It also doesn't rule out varying speed of light theories whose first order correction is quadratic in the speed of light.

This very discussion on the 31GeV photon appeared in several blogs and even here a few months ago due to a preprint that showed on the arxiv.org. I thought that preprints to Nature articles were embargoed at least until the day of their publication. So, it's weird that this article showed up in Nature.

 

[ZapperZ]

It also doesn't rule out varying speed of light theories whose first order correction is quadratic in the speed of light.

This very discussion on the 31GeV photon appeared in several blogs and even here a few months ago due to a preprint that showed on the arxiv.org. I thought that preprints to Nature articles were embargoed at least until the day of their publication. So, it's weird that this article showed up in Nature.

No, that's a myth.

Nature doesn't embargo preprints appearing, even in ArXiv. But you run the risk of some news media picking it up, and when that occurs, then the fact that it has been covered in another media will cause it to be disqualified from Nature and Science.

See this thread:

https://www.physicsforums.com/showthread.php?t=325116

Zz.

 

[atyy]

No, that's a myth.

Nature doesn't embargo preprints appearing, even in ArXiv. But you run the risk of some news media picking it up, and when that occurs, then the fact that it has been covered in another media will cause it to be disqualified from Nature and Science.

See this thread:

https://www.physicsforums.com/showthread.php?t=325116

Zz.

The link http://www.nature.com/authors/editorial_policies/embargo.html you gave on the other thread seems to say that it is not a problem if other media pick it up from arXiv - it's only a problem if authors discuss it with other media.

In fact, this article was picked up by other media from arXiv before publication in Nature:
http://motls.blogspot.com/2009/08/fermi-kills-all-lorentz-violating.html
http://backreaction.blogspot.com/2009/08/that-photon-from-grb090510.html
http://egregium.wordpress.com/2009/08/17/news-from-fermi-formerly-glast/[/URL]

 

[atyy]

So whose quantum gravity theory will crash-and-burn if this is correct?

http://physicsworld.com/cws/article/news/40834

Zz.

Yours! (I believe you're rooting for condensed matter? ) AdS/CFT will still survive, if you consider that condensed matter. These guys are still trying to get realistic cosmologies out of it http://arxiv.org/abs/0908.0756 .

 

[ZapperZ]

Yours! (I believe you're rooting for condensed matter? ) AdS/CFT will still survive, if you consider that condensed matter. These guys are still trying to get realistic cosmologies out of it http://arxiv.org/abs/0908.0756 .

I'm rooting for condensed matter, and therefore, I have a quantum gravity theory?

I think this deserves zero response.

Zz.

 

[ZapperZ]

The link http://www.nature.com/authors/editorial_policies/embargo.html you gave on the other thread seems to say that it is not a problem if other media pick it up from arXiv - it's only a problem if authors discuss it with other media.

In fact, this article was picked up by other media from arXiv before publication in Nature:
http://motls.blogspot.com/2009/08/fermi-kills-all-lorentz-violating.html
http://backreaction.blogspot.com/2009/08/that-photon-from-grb090510.html
http://egregium.wordpress.com/2009/08/17/news-from-fermi-formerly-glast/[/URL][/QUOTE]

Those are bloggers, not the media. The embargo policy does not prohibit academic exchange or discussion of the paper. I've had a long discussion with one of Nature's associate editor a while back asking for clarification of this policy, and what I've stated is what I've understood based on not only their stated policy, but also from that discussion.

You should also factor in the DATE that the manuscript was accepted for publication, and when it appeared on ArXiv. Many authors who submitted their work to Science or Nature will upload the manuscript AFTER receiving acceptance. I know that we did that.

Zz.

 

[humanino]

<mood=nitpicking>I'd be interested to know which theory they are referring to

certain theories of quantum gravity that postulate the violation of Lorentz invariance.

I know there are specific models which do so, but from the onset those are working hypothesis to see what comes out, not really "postulates". The way I see it, the hypothesis is used to shortcut the time necessary to decide whether Lorentz violations are predicted to happen as breaking of the symmetry from the postulates themselves.</mood>

 

[tom.stoer]

Some months ago I asked regarding the current status of nnon-trivial dispersion relation in LQG / SF theories. A couple of years ago these theories seemed to propose
- non-trivial dispersion relations, related to DSR in some semiclassical limit
- perhaps GZK violation
- polarization effects in CBR
These predictions depend on the semiclassical state which is still not known and therefore everything was speculative. I haven't seen any new or updated paper regarding these subjects for months (or even years), neither on arxiv nor in any journal.

So what is the current status of these theories?

If their predictions are negative (which would agree with the above mentioned experiment): do these theories run into the same problem as string theory, namely to make post-dictions only?

 

[marcus]

Some months ago I asked regarding the current status of nnon-trivial dispersion relation in LQG / SF theories. A couple of years ago these theories seemed to propose
- non-trivial dispersion relations, related to DSR in some semiclassical limit
- perhaps GZK violation
- polarization effects in CBR
These predictions depend on the semiclassical state which is still not known and therefore everything was speculative. I haven't seen any new or updated paper regarding these subjects for months (or even years), neither on arxiv nor in any journal.

So what is the current status of these theories?

...

We could start a separate thread about prospects (are there any?) for cosmological tests of Loop/Foam theory or theories.

If you are asking a general question about loop/foam status, then in my opinion the most significant current research is aimed (not at distinguishing between several theories but) at simply getting one background independent theory with the right classical limit.

Accordingly you see major papers aimed at either merging different lines of investigation or establishing the classical limit.
Lewandowski reconciling loop and foam models, to form a single combined approach.
Ashtekar and others extending loop cosmology to anisotropic cases--relaxing assumptions.
Ashtekar trying out spin foam cosmology.
Rovelli's group checking to see that the limits are right.On the other hand, in terms of raw numbers of papers, I think cosmology is the biggest area of loop/foam research growth. Many of the papers are by comparative newcomers to the field, and are groping for observable consequences.
There are still only a comparatively small number of researchers, but that's where I see percentage growth. Judging from the recent literature, if there is any hope of detecting a loop/foam signature in the near term, it would be in the cosmic microwave background, the universe's history of expansion/structure formation, and possibly other astrophysics.

You mentioned dispersion, energy-dependent speed of signal propagation. I think you are right that there has been substantially no interest in that for several years in the loop/foam research community as a whole. A number of people worked on it around 2005-2006 but couldn't get any clear predictions.

You mentioned CMB polarization. I will try to hunt up some papers about that. There have been some, but i don't recall any making definite predictions.
If someone is interested they might have a look at this guy's papers:
http://arXiv.org/find/gr-qc/1/au:+Mielczarek_J/0/1/0/all/0/1
He publishes in Physical Review D, Physics Letters B, General Relativity and Gravitation, JHEP. JCAP,
and he seems to be focusing on deriving some kind of observable signs of LQC.

 

[marcus]

So what is the current status of these theories?

If their predictions are negative (which would agree with the above mentioned experiment): do these theories run into the same problem as string theory, namely to make post-dictions only?

The second most highly cited Loop Foam paper for this year is by Aurelien Barrau and Julien Grain and concerns the effort to derive prediction of a "cosmological footprint" in the CMB. Probably last year no one reading this thread had heard of Barrau and Grain. This indicates the rate at which new researchers are entering the field and can quickly gain recognition.

Barrau is associate prof at Grenoble. He has some 3 papers in Loop Cosmology so far, just in this year. They represent 3 out of his 4 most recent papers.
http://lpsc.in2p3.fr/ams/aurelien/index_eng.html
http://arxiv.org/find/grp_physics/1/au:+Barrau_A/0/1/0/all/0/1
Barrau has published over 50 papers and some of his earlier work was string-related.

As far as I can see, Barrau and Grain do not give exact quantitative predictions of what the recently launched Planck spacecraft 's data will show---but they make some qualitative statements. I consider this to be work in progress---that indicates where the field is going in the empirical testing department. Anyone interested can look at their "LQG footprints" paper.
http://arxiv.org/abs/0902.0145
Cosmological footprints of loop quantum gravity
J. Grain, A. Barrau
Accepted by Phys. Rev. Lett., 7 pages, 2 figures
(Submitted on 2 Feb 2009)
"The primordial spectrum of cosmological tensor perturbations is considered as a possible probe of quantum gravity effects. Together with string theory, loop quantum gravity is one of the most promising frameworks to study quantum effects in the early universe. We show that the associated holonomy correction should modify the potential seen by gravitational waves during the inflationary amplification. The resulting power spectrum should exhibit a characteristic tilt. This opens a new window for cosmological tests of quantum gravity."

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

In post #15 I gave a link to the papers of Jakob Mielczarek. He also is working on deriving from LQG an observable-in-CMB signature. Barrau et al cite him. I think his name is pronouced MYEL-CHA-REK. He has several recent papers about this, here are two:
http://arXiv.org/abs/0902.2490
Tensor power spectrum with holonomy corrections in LQC
http://arXiv.org/abs/0908.4329
The Observational Implications of Loop Quantum Cosmology

 

[hamster143]

You mentioned dispersion, energy-dependent speed of signal propagation. I think you are right that there has been substantially no interest in that for several years in the loop/foam research community as a whole. A number of people worked on it around 2005-2006 but couldn't get any clear predictions.

There's a relatively recent ('08) article that basically states that LQG is only able to calculate the correct classical value of black hole entropy if the first-order term in the dispersion equation (the one constrained by FERMI) vanishes exactly.

Of course, no one knows if the classical value of black hole entropy is correct, because no one has so much as seen a black hole, let alone measure its entropy ...

 

[tom.stoer]

thanks a lot