Editing Goddard–Thorn theorem (section)

{{Short description|Theorem in string theory}}
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In [[mathematics]], and in particular in the mathematical background of [[string theory]], the '''Goddard–Thorn theorem''' (also called the '''no-ghost theorem''') is a theorem describing properties of a [[functor]] that quantizes [[bosonic strings]]. It is named after [[Peter Goddard (physicist)|Peter Goddard]] and [[Charles Thorn]].

The name "no-ghost theorem" stems from the fact that in the original statement of the theorem, the natural [[inner product]] induced on the output vector space is positive definite. Thus, there were no so-called [[Ghosts (physics)|ghosts]] ([[Pauli–Villars regularization|Pauli–Villars ghosts]]), or vectors of negative norm. The name "no-ghost theorem" is also a word play on the [[no-go theorem]] of quantum mechanics.