# Alternative Critical Dimensions in String Theory

Is it possible to write down a Lagrangian for a string theory with a critical dimension different than the familiar 10 or 26? How could one find a string theory Lagrangian for a given dimension? Could you prove that no string theory exists for a given critical dimension?

• I think you should ask these 3 questions as separate ones, and not in the same post. – user28355 Jan 19 '14 at 1:58
• @DavidZ as the overarching topic is how the critical dimension is constrainrd in ST it seems to that a good answer ( I have a vague feeling along which way it might go...) could answer the whole question since its parts are related enough. – Dilaton Jan 19 '14 at 6:54

You write a lagrangian for a string propogating in $(d,1)$ dimensional spacetime and notice that it is equivalently a 2d conformal field theory on the worldsheet of the string. Consistency conditions (vanishing of the conformal anomaly) then imply that necessary dimension of spacetime be 26 for bosonic string theory and 10 for superstring theory.