## Wednesday, January 11, 2006

### Herman Verlinde's picture

The LHC olympics people from the whole East Coast have come to Harvard to play their games and listen to various lectures about the evaluation of the fictitious LHC data that is going to become real data in less than two years.

That's a good opportunity for interesting debates - even for those of us who are very busy right now.

We have talked with Herman Verlinde and it was fun. First of all, we were teaching the same course (Quantum Mechanics II) so we were exchanging experience with quantum computers, entangled states, and Herman taught me about the three-spin-1/2 "GHZ" state that maximally violates locality in the EPR sense. Very interesting.

Decoupling of open strings

Herman has also explained the true nature of the "bet that string theory is correct" that Peter Woit copied from P.P. Cook's blog. The reality was a bit different and more technical.

Herman argued that it would be unreasonable to bet against the statement that open string theory contains the Standard Model. Why did we use the adjective "open" in the previous sentence? Herman proposes the following picture:
• it is extremely unlikely that the accelerators such as the LHC that will be available in the near future will measure anything such as quantum gravity
• this should mean that gravity, an important part of closed string dynamics should be decoupled
• he believes that the rest of physics - the Standard Model and beyond - should therefore be interpreted as decoupled dynamics of open strings
• open strings propagating around a specific singularity could and should give you this Standard Model or its extension
• quantum gravity and the Planckian completion is obtained by embedding the singularity into a bigger theory - a compact "Calabi-Yau" manifold
This line of reasoning of course does not prove that other scenarios - where the Standard Model is made of closed strings or other objects - are impossible. But it may be the most natural and "minimal" decoupling of gravity from the rest. Moreover, Herman argues that in this picture, it is more or less guaranteed that the QCD string should be identified with the fundamental closed string. I still don't quite follow why it must be the same type of the string, but it is conceivable that he has an argument.

See their paper with Martijn Wijnholt for a specific construction of the Standard Model on a D3-brane.

Incidentally, Herman also says that in the decoupled picture of particle physics, gauge-invariant fields like the parameters of the Standard Model don't acquire any potential - since the potential is inherently a closed string effect. This would mean that getting the right spectrum is enough to find a realistic candidate. The couplings are only determined once the compact manifold and the closed string field stabilization is calculated. So you have a theory that you can't prove or disprove for some time - a "not even wrong" theory - which Herman believes to be essentially a good thing.

Herman Verlinde is the twin brother of Erik Verlinde who will claim that gravity doesn't exist in 2010.

#### 1 comment:

1. As a biproduct of my hep-ph/0512065, I feel some new sympathy for open strings. If we ask

a) that only quark or antiquarks can attach to the extremes of the open string
b) that there are three generations and
c) that the top quark is unable to attach itself to the extreme of the string

Then the number of degrees of freedom of the scalar combinations having electric charge 1, 2/3 and 1/3 seems to coincide, charge-by-charge, with the number of fermion degrees of freedom of the standard model. If this is an invitation to supersymetry in the open string, I can not tell.