The Type 0 string theory is a less well-known model of string theory. It is a

superstring theory Superstring theory is an attempt to explain all of the particles and fundamental forces of nature in one theory by modeling them as vibrations of tiny supersymmetric strings. 'Superstring theory' is a shorthand for supersymmetric string t ...

in the sense that the

worldsheet In string theory, a worldsheet is a two-dimensional manifold which describes the embedding of a string in spacetime. The term was coined by Leonard Susskind as a direct generalization of the world line concept for a point particle in special a ...

theory is supersymmetric. However, the

spacetime In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differ ...

spectrum is not supersymmetric and, in fact, does not contain any fermions at all. In dimensions greater than two, the ground state is a

tachyon A tachyon () or tachyonic particle is a hypothetical particle that always travels faster than light. Physicists believe that faster-than-light particles cannot exist because they are not consistent with the known laws of physics. If such partic ...

so the theory is unstable. These properties make it similar to the

bosonic string Bosonic string theory is the original version of string theory, developed in the late 1960s and named after Satyendra Nath Bose. It is so called because it contains only bosons in the spectrum. In the 1980s, supersymmetry was discovered in the co ...

and an unsuitable proposal for describing the world as we observe it, although a GSO projection does get rid of the tachyon and the even

G-parity In particle physics, G-parity is a multiplicative quantum number that results from the generalization of C-parity to multiplets of particles. ''C''-parity applies only to neutral systems; in the pion triplet, only π0 has ''C''-parity. On the othe ...

sector of the theory defines a stable string theory. The theory is used sometimes as a

toy model In the modeling of physics, a toy model is a deliberately simplistic model with many details removed so that it can be used to explain a mechanism concisely. It is also useful in a description of the fuller model. * In "toy" mathematical models ...

for exploring concepts in string theory, notably closed string

tachyon condensation A tachyon () or tachyonic particle is a hypothetical particle that always travels faster than light. Physicists believe that faster-than-light particles cannot exist because they are not consistent with the known laws of physics. If such parti ...

. Some other recent interest has involved the two-dimensional Type 0 string which has a non-perturbatively stable matrix model description. Like the Type II string, different GSO projections result in slightly different theories, Type 0A and Type 0B. The difference lies in which types of Ramond–Ramond fields lie in the massless spectrum.

References

* Polchinski, Joseph (1998). ''String Theory'', Cambridge University Press. A modern textbook. ** Vol. 2: Superstring theory and beyond. . String theory {{string-theory-stub