The N=4 string is the same as the N=2 string

TL;DR

This paper demonstrates that the quantized N=4 string, accounting for reducible constraints, is equivalent to the N=2 string with critical dimension four, highlighting advantages like classical field equations and manifest covariance.

Contribution

It shows the equivalence of the N=4 and N=2 strings when properly quantized, revealing advantages of the N=4 formulation such as classical equations and manifest covariance.

Findings

N=4 string reduces to N=2 string upon proper quantization

N=4 formulation has classical field equations and manifest covariance

Theory includes fermions and suggests spacetime supersymmetry

Abstract

We redo the quantization of the N=4 string, taking into account the reducibility of the constraints. The result is equivalent to the N=2 string, with critical dimension D=4 and signature (++--). The N=4 formulation has several advantages: the sigma-model field equations are implied classically, rather than by quantum/beta-function calculations; self-duality/chirality is one of the super-Virasoro constraints; SO(2,2) covariance is manifest. This reveals that the theory includes fermions, and is apparently spacetime supersymmetric.