About the origins of the Supersymmetric Standard Model

Could one use supersymmetry to relate the fermions, constituants of matter, with the bosons messengers of the interactions? This is, ideally, what a symmetry between fermions and bosons would be expected to do. However many obstacles seemed, long ago, to prevent supersymmetry from possibly being a fundamental symmetry of Nature. Which fermions and bosons could be related? Is spontaneous supersymmetry breaking possible at all? If yes, where is the corresponding spin-1/2 Goldstone fermion? Supersymmetric theories also involve Majorana fermions, unknown in Nature. And how could we define conserved quantum numbers like B and L, when these are carried by fundamental (Dirac) fermions only, not by bosons? An early attempt to relate the photon with a ``neutrino'' led us to R-invariance and to a new R quantum number carried by the supersymmetry generator, but this ``neutrino'' had to be reinterpreted as a new particle, the photino. We also had to introduce bosons carrying ``fermion numbers'' B and L, which became the squarks and sleptons. This led to the Supersymmetric Standard Model, involving SU(3) x SU(2) x U(1) gauge superfields interacting with chiral quark and lepton superfields, and two doublet Higgs superfields responsible for quark and lepton masses. R-parity, deeply related with B and L conservation laws, appeared as a remnant of the original R-invariance, reduced to a discrete symmetry so that the gravitino and gluinos can acquire masses. We also comment about supersymmetry breaking.