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.

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    $\begingroup$ 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. $\endgroup$ – Ron Maimon Aug 25 '11 at 1:07
  • $\begingroup$ The string picture of NS and R models dates from 1974. dx.doi.org/10.1016/0550-3213(74)90127-8 $\endgroup$ – Mitchell Porter Aug 25 '11 at 2:38
  • $\begingroup$ +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? $\endgroup$ – arivero Aug 25 '11 at 17:43
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    $\begingroup$ 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. $\endgroup$ – Ron Maimon Aug 26 '11 at 5:51
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    $\begingroup$ 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. $\endgroup$ – Mitchell Porter Aug 27 '11 at 12:05

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.

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  • $\begingroup$ 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. $\endgroup$ – arivero Sep 4 '11 at 12:13
  • $\begingroup$ And in fact the NSR string was originally called the "spinning string", not the "superstring". It is not an input but a key result (prediction) of the assumption of strings paired with the existence of fermions that 1. the worldsheet theory is supersymmetric (which is easy to see) 2. also the spacetime theory is supersymmetric (which comes as a miracle for the NSR string and is only explained by the Green-Schwarz string). $\endgroup$ – Urs Schreiber Aug 22 '16 at 17:09

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