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

string theory In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and intera ...

. 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 theory is supersymmetric. However, the

spacetime In physics, spacetime, also called the space-time continuum, is a mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams are useful in visualiz ...

spectrum is not supersymmetric and, in fact, does not contain any

fermion In particle physics, a fermion is a subatomic particle that follows Fermi–Dirac statistics. Fermions have a half-integer spin (spin 1/2, spin , Spin (physics)#Higher spins, spin , etc.) and obey the Pauli exclusion principle. These particles i ...

s 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, faster than light. Physicists posit that faster-than-light particles cannot exist because they are inconsistent with the known Scientific law#L ...

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

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

toy model A toy or plaything is an object that is used primarily to provide entertainment. Simple examples include toy blocks, board games, and dolls. Toys are often designed for use by children, although many are designed specifically for adults and ...

for exploring concepts in string theory, notably closed string

tachyon condensation Tachyon condensation is a process in particle physics in which a system can lower its potential energy by spontaneously producing particles. The end result is a "condensate" of particles that fills the volume of the system. Tachyon condensation is ...

. 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