Lorentz Invariance Violation?

[Martin]

http://arxiv.org/abs/0708.2250

Lorentz Invariance Violation from String Theory

Nikolaos E. Mavromatos (King's College London)26 pages 3 figures. Invited talk at the International Workshop 'From Quantum to Emergent Gravity: Theory and Phenomenology', SISSA, Trieste (Italy), June 11-15 2007

(Submitted on 16 Aug 2007)

 

"In this brief, and by no means complete, review I discuss situations in string theory, in which Lorentz Invariance Violation may occur in a way consistent with world-sheet conformal invariance, thereby leading to acceptable, in principle, string backgrounds. In particular, I first discuss spontaneous Lorentz violation in (non supersymmetric) open string field theory. Then, I move onto a discussion of gravity-induced modified dispersion relations in non-critical (Liouville) strings, in the sense of an induced Finsler-like geometry depending on both coordinates and momenta, for string propagation in non-trivial space times (such as D-particle 'foamy situations'). I pay attention to explaining the appearance of bi-metric models from such string theories, which could serve as examples of alternative scenaria to dark matter. Finally, I make some comparisons with similar developments in other contexts, such as critical strings in non-commutative space times, as well as deformed special relativities and theories with reduced Lorentz symmetry, advocated recently, where again Finsler geometry seems to come into play. In this latter respect, I put the emphasis on phenomenology and attempt to answer the question as to whether there is the possibility of experimental disentanglement of the various approaches."

 

 

Any comment? Until 2006 the Loop community was doing a bunch of research on DSR (deformed special relativity) and the possibility of observing very slight dispersion effects in GRB (gammaray bursts).

 

But in 2006 there seems to have been a general conclusion that none of the nonstring QG approaches predict observations of Lorentz Invariance Violation.

So at the Loops 07 conference there were NO DSR papers!

As far as I know, the possibility of L.I.V. was not discussed.

 

So here is a turnaround! It sounds like Nick Mavromatos is suggesting that some versions of string predict L.I.V.

 

There is an important GRB instrument scheduled to fly in 2008. time to place your bets now Will GLAST see energy-dependent speed of light or not?

[CPL.Luke]

hmm I remember that a few years ago somebody predicted an energy dependant speed of light in Variable Speed of Light theory or VSL, as far as I know they didn't reference any string related approaches, is it possible that we could observe the spectra and have it only indicate an aleration to the lorentz transformation and in turn GR?

[Martin]

Hi Luke,

there are modifications of special relativity called DSR which do not actually BREAK lorentz invariance in the sense of having a preferred frame but which have a curved tangent space so the addition of momenta is ever so slightly different

 

In DSR theories one can either get an energy-dependent speed of light or NOT. this is confusing. If you get an energy dependent speed of light, then in the versions I have seen it is such a slight variation that one can only see it in a GRB signal after the signal has been traveling on the order of a billion years. It takes that long for the faster photons to get measurably out in front of the slower ones.

 

but until 2005 or 2006 I was seeing papers where people were looking forward to the GLAST launch (a GRB satellite) and hoping to be able to derive dispersion relations (energy-dependent speed) from some of their theories.

So those theories that predicted it would be vindicated, or else falsified.

 

Laurent Freidel managed to prove that a certain spinfoam model predicted DSR dispersion BUT ONLY IN 3D. In 2006 he tried hard to extend the result to 4D. He and collaborators ran into insuperable difficulties.

 

In the end, non-string QG was unable to come up with a firm prediction that the speed of light should be slightly higher for very energetic gamma.

 

So the whole thing DIED. At Loops '07 there was only one invited talk (by Sabine Hossenfelder) that dealt with DSR. Earlier I thought there were no talks, but I just now listened to her talk.

 

She mentioned "minimal length" and investigated the phenomenology, what to expect from accelerator LHC and astronomical observations if there was one.

 

I sense that she was slightly abashed to find that she was the ONLY invited speaker there who was talking about minimal length, DSR etc.

 

It is maybe a little frustrating. On the whole I am glad because the leading edge research is in sectors where there is DEFINITELY NO MINIMAL LENGTH or variable speed of light-----Reuter's approach has become very influential and it agrees with Freidel 4D spinfoam case and with the Triangulations approach and so on.

 

So by dropping the minimal length idea, one can get more convergence between the various approaches.

 

But it is still somehow disappointing.

 

Now it seems if one wants to find a theory that predicts Lorentz Violation one has to go over into Stringland. As per Nick Mavromatos paper. And that I suppose is apt to be confusing because so many different versions of theory.

String impresses me as more of a FRAMEWORK for constructing theories than as an actual theory.

 

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

BTW you mentioned VSL. Several years back Magueijo cooked up a VSL cosmology, but he later abandoned it and has not written any VSL cosmology papers for some years now. Its always good to try alternatives, as he did, but standard cosmology works well and is difficult to construct alternatives. He has been writing good papers on other things---he's smart and has lots of ideas.

[Severian]

Lorentz symmetry IS violated, and it is a well know, experimentally verified fact. A parity inversion is a form of improper Lorentz transformation and since the SM violates parity, it is not invariant under improper Lorentz transformations.

[Martin]

that's certainly right Severian. If one wants to make the distinction between proper and improper and include improper as violations, then we already have a certain type of Lorentz violation.

 

One really ought to define terms. In my experience the research papers about tests of Lorentz invariance violation are not talking about what you say, they are more likely to be talking about the existence or not of a preferred frame, or of deformations of Lorentz symmetry which are more radical than what you say and have not been observed.

[BenTheMan]

Severian---

 

Parity and Time Reversal aren't continuously related to the identity---they are discrete symmetries of space-time. So I don't quite agree with saying ``The GWS lagrangian maximally violates CP, so the SM violates Lorentz Invariance''. I think I agree with Martin---Lorentz Invariance violations are generally taken to mean breaking the Lorentz Group itself.

[Severian]

Well, I was being a bit tongue in cheek, but a parity transformation most certainly IS defined as a Lorentz transformation. The fact that it is not connected to the identity is why it is called 'improper'.

[Farsight]

Interesting thread. Thanks Martin.