Goodard-Thorn no-ghost theorem



In string theory the Goddard-Thorn theorem (Goddard-Thorn 72, Thorn 87, Thorn 12) establishes the consistency of the usual quantization of the bosonic string sigma-model for target space dimension 26, and of the NSR superstring sigma-model for target space dimension 10.

In the original “old covariant quantization” approach to this problem the proof amounts to demonstrating that the inner product on the would-be Hilbert space of quantum states is indeed positive definite. Since would-be quantum states of negative norm have been known as “ghost states”, the theorem has become widely known as the no-ghost theorem of string theory. More modern derivations proceed via or compare to quantization via the BRST complex of the string sigma-model.

In particular the theorem thus establishes the superstring excitations of vanishing mass, and that these coincide with the quanta of perturbative supergravity in 10 dimensions (type IIA supergravity or type IIB supergravity).


The original articles are

The proof via DDF operators is also recalled in

See also