Spacetime supersymmetry of extended fermionic strings in 2+2 dimensions

The N=2 fermionic string theory is revisited in the light of its recently proposed equivalence to the non-compact N=4 fermionic string model. The issues of spacetime Lorentz covariance and supersymmetry for the BRST quantized N=2 strings living in uncompactified 2+2 dimensions are discussed. The equivalent local quantum supersymmetric field theory appears to be the most transparent way to represent the spacetime symmetries of the extended fermionic strings and their interactions. The considerations support Siegel's (1992) ideas about the presence of SO(2,2) Lorentz symmetry as well as at least two self-dual spacetime supersymmetries in the theory of N=2(4) fermionic strings, though the authors do not have a compelling reason to argue for the necessity of maximal spacetime supersymmetry. The worldsheet arguments for the absence of all massive string modes in the physical spectrum and the vanishing of all string-loop amplitudes in the Polyakov (1981) approach, are given on the basis of the general consistency of the theory.