In string theory, type 0 refers to perturbative string theories where the strings themselves are superstrings (hence have supersymmetry on their worldsheet) but their target spacetime effective field theory is not supersymmetric, in fact does not even contain any fermion fields.
Technically, this comes from one particular choice of GSO projection of the superstring which breaks all target space supersymmetry. Concretely, the possible GSO projection for the critical NSR superstring yield, besides the supersymemtric type IIA and type IIB string theory, two type 0 theories, now called type 0A and type 0B. On the other hand, for the heterotic string there are seven type 0 versions.
All but one of these type 0 theories have a tachyon mode in the closed string sector of the standard Minkowski spacetime vacuum and thus look like perturbations about unstable backgrounds (cf. tachyon condensation). The one exception is the type 0 heterotic string with gauge group . (Dixon & Harvey 1986, Seiberg & Witten 1986, Kawai, Lewellen & Tye 1986).
However, it was argued by Klebanov & Tseytlin 1999a that in nontrivial RR field backgrounds the tachyon mode may disappear, rendering these backgrounds stable, and indeed bulk duals to certain non-supersymmetric CFTs (Klebanov & Tseytlin 1999b).
Original discussion (not yet using the term “type 0”):
Lance J. Dixon, Jeffrey A. Harvey: String Theories in Ten-Dimensions Without Space-Time Supersymmetry, Nucl. Phys. B 274 (1986) 93-105 [10.1016/0550-3213(86)90619-X]
Nathan Seiberg, Edward Witten, section 4 of: Spin Structures in String Theory, Nucl. Phys. B 276 (1986) 272 [doi:10.1016/0550-3213(86)90297-X]
Hikaru Kawai, D. C. Lewellen, S. H. H. Tye: Classification of Closed Fermionic String Models, Phys. Rev. D 34 (1986) 3794 [doi:10.1103/PhysRevD.34.3794]
See also:
On D-branes in type 0 string theory:
Igor Klebanov, Arkady A. Tseytlin: D-Branes and Dual Gauge Theories in Type 0 String Theory, Nucl. Phys. B 546 (1999) 155-181 [arXiv:hep-th/9811035, doi:10.1016/S0550-3213(99)00041-3]
Igor R. Klebanov, Arkady A. Tseytlin: A Non-supersymmetric Large CFT from Type 0 String Theory, JHEP 9903:015 (1999) [arXiv:hep-th/9901101, doi:10.1088/1126-6708/1999/03/015]
(in relation to AdS/CFT duality)
Marco Billó, Ben Craps, Frederik Roose: On D-branes in Type 0 String Theory, Phys. Lett. B 457 (1999) 61-69 [arXiv:hep-th/9902196, doi:10.1016/S0370-2693(99)00508-0]
Mohammad R. Garousi: String Scattering from D-branes in Type 0 Theories, Nucl.Phys. B 550 (1999) 225-237 [arXiv:hep-th/9901085, doi:10.1016/S0550-3213(99)00152-2]
Ralph Blumenhagen, Anamaria Font, Dieter Lüst: Non-Supersymmetric Gauge Theories from D-Branes in Type 0 String Theory, Nucl. Phys. B 560 (1999) 66-92 [arXiv:hep-th/9906101, doi:10.1016/S0550-3213(99)00443-5]
Eduardo Eyras: Stable D8-branes and Tachyon Condensation in Type 0 Open String Theory, JHEP 9910 (1999) 005 [arXiv:hep-th/9908121, doi:10.1088/1126-6708/1999/10/005]
Discussion of possible K-theory classification of D-brane charge in type 0 string theory:
Justin Kaidi, Julio Parra-Martinez, Yuji Tachikawa: Classification of String Theories via Topological Phases, Phys. Rev. Lett. 124 (2020) 121601 [doi:10.1103/PhysRevLett.124.121601]
Justin Kaidi, Julio Parra-Martinez, Yuji Tachikawa: Topological Superconductors on Superstring Worldsheets, SciPost Phys. 9 010 (2020) [doi:10.21468/SciPostPhys.9.1.010, arXiv:1911.11780]
On possible relation of type 0 to M-theory:
Application of type 0 strings to holographic QCD:
Roberto Grena, Simone Lelli, Michele Maggiore, Anna Rissone, Confinement, asymptotic freedom and renormalons in type 0 string duals, JHEP 0007 (2000) 005 (arXiv:hep-th/0005213)
Mohammad Akhond, Adi Armoni, Stefano Speziali, Phases of from Type 0 Strings and Seiberg Duality (arxiv:1908.04324)
Proposed relation to M-theory KK-compactified on the wedge sum of two circles:
Last revised on March 20, 2026 at 10:21:33. See the history of this page for a list of all contributions to it.