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Was there some phenomenological motivation for Ramond and Neveu-Swarz models?

+ 2 like - 0 dislike
40 views

This remark from Lubos puzzles me

Ramond's string - and Neveu-Schwarz string - wasn't really an "origin of string theory". String theory had "origin" as bosonic string theory which has no fermions. All SUSY/fermioncs strings are "new".

How to fit this view, which seems to be the common one, with the fact that the R and NS papers date from 1971, before the concept of supersymmetry, long before superstrings themselves, and only three years later than the Veneziano model, and almost simultaneous (less than two years) with the idea of a String interpretation of the model?

Were the R-NS models just a hep-th proposal, without any link to, nor motivation from, phenomenology? It could be so. I can not find any clear reference to baryonic regge trajectories in the early literature, and I can not find any duality diagram involving fermions, before 1971. But on other hand, Susskind 1970 abstracts keep speaking of "model of hadrons", not just "mesons", when exposing the idea of strings. So perhaps I am just being sloppy in my spires searches.

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user arivero
asked Aug 24, 2011 in Phenomenology by - (250 points) [ no revision ]
The Ramond proposal was inspired by the desire to incorporate fermions, but there were stringent constraints on this, and he had to develop both a string picture and supersymmetry. Lubos is not a historian, and doesn't claim to be.

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user Ron Maimon
The string picture of NS and R models dates from 1974. dx.doi.org/10.1016/0550-3213(74)90127-8

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user Mitchell Porter
+Mitchell Porter, I am not sure if this goes against my line of thought, as it proves that as soon as the NS-R model did appear, an effort was done to incorporate it into the framework of string interactions. The 1974 paper is actually a follow-up to Mandelstam 1973 "Interacting String Picture Of Dual Resonance Models", isn't it?

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user arivero
Ramond's "string picture" is not as sophisticated as Mandelstam's. Mandelstam is really finding a complete dynamical system. Ramond's paper introduced an "internal time" coordinate which was either periodic or an interval, I forget, which allowed him to expand states in a heuristic creation operators. He did not describe dynamics using this picture, but used it to get Fermion Regge trajectories using what we would call supersymmetry generators, the F operators which complete the super-virasoro algebra, which cancel ghosts.

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user Ron Maimon
Ron, I would like to discuss your views on Chew's (and Mandelstam's) relevance for string theory, but have no way to contact you... I am not aware of any deductive path to superstrings that doesn't begin by positing an extended object. The path from the bootstrap, via DHS duality and the Veneziano amplitude, to string theory, was inductive, and yet isn't the bootstrap ultimately supposed to be deductive?

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user Mitchell Porter
Now maybe there is a deductive path to the string which just looks at the S-matrix (or its analogues in (anti) de Sitter space). It's a worthy topic of investigation, but no such derivation presently exists. Meanwhile, elsewhere I've seen you suggest that the holographic principle is string theory's counterpart of the equivalence principle. Again, an interesting idea, but I'd like to see how it's supposed to work in detail.

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user Mitchell Porter
@Mitchell--- The point of the comments I make about Chew/Mandelstam is to correct the historical injustice of their marginalization. There is no full deductive path to string theory, period. All derivations assume that some sort of string action produces the entire S-matrix spectrum, so that a worldsheet field theory gives the whole physics. This assumption is correct, but is not justified only by the reasoning that the string is extended.

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user Ron Maimon

1 Answer

+ 4 like - 0 dislike

The statement that bosonic strings came first and Fermionic strings came later is not exactly correct as history. Fermionic strings came almost simultaneously, when Ramond discovered the two dimensional super-conformal algebra in 1971.

Ramond style string theories did not have space-time supersymmetry (or rather, they did, but the GSO projection which was required to extract the physical spectrum was not discovered until 1976, and the proof that this projection actually leaves a sensible theory did not come until the Green-Schwarz formulation was developed in the early 1980s).

The Neveu Schwarz paper analyzes bosonic oscillations of a fermionic string, and was motivated by exploring all consistent bootstraps to find something that would work for the light mesons. The problems at the time was that a bosonic tachyon was interpreted as the experimentally known instability of the pion vacuum, so it was considered essential for a good theory. The Neveu-Schwarz sector, without the GSO projection, contains such a tachyon. Now we know that this means that the theory is sick, but back then, it was considered a good sign.

The Ramond fermions were then interpreted as bare baryons, to be dressed with the pion condensation, and this interpretation is also wrong, since baryons have a three-quark symmetry structure. The Neveu-Schwarz sector was interpreted as mesons, but they also had a tachyon (which is GSO odd and vanishes), and nothing looks like the QCD spectrum, not with the crude tools available then.

The inconsistency of Ramond-Neveu-Schwarz strings was expressed most simply by Edward Witten in the early eighties: the closed string sector of a fermionic string contains massless spin-3/2 particles, so it must couple to some space-time supercurrent in order to make sense. The graviton and spin 3/2 gravitinos must make a sensible supergravity theory. The development of supergravity was initiated to a large degree by string theory, since Scherk immediately began to investigate supergravities after GSO. He probably understood even then that the low-energy limit of superstrings would have to be some sort of supergravity.

So it is most fair to say that the development of superstrings and of bosonic strings went hand in hand, but the full perturbation series for the bosonic string was completed earlier, while a full perturbation theory of the fermionic string had to wait until the early eighties.

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user Ron Maimon
answered Sep 4, 2011 by Ron Maimon (7,295 points) [ no revision ]
Yep, GSO projection is a main ingredient, and it comes later! As for interpretations, there are also some early ones where they try to look at the Ramond sector as if they where quarks, and this view seems to travel along with the "baryon view" during the 71-74 period.

This post imported from StackExchange Physics at 2014-03-07 14:32 (UCT), posted by SE-user arivero

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