Type II string theory

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In theoretical physics, type II string theory is a unified term that includes both type IIA strings and type IIB strings theories. Type II string theory accounts for two of the five consistent superstring theories in ten dimensions. Both theories have ${\mathcal {N}}=2$ extended supersymmetry which is maximal amount of supersymmetry — namely 32 supercharges — in ten dimensions. Both theories are based on oriented closed strings. On the worldsheet, they differ only in the choice of GSO projection.

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Type IIA string theory

At low energies, type IIA string theory is described by type IIA supergravity in ten dimensions which is a non-chiral theory (i.e. left–right symmetric) with (1,1) d=10 supersymmetry; the fact that the anomalies in this theory cancel is therefore trivial.

In the 1990s it was realized by Edward Witten (building on previous insights by Michael Duff, Paul Townsend, and others) that the limit of type IIA string theory in which the string coupling goes to infinity becomes a new 11-dimensional theory called M-theory.^[1] Consequently the low energy type IIA supergravity theory can also be derived from the unique maximal supergravity theory in 11 dimensions (low energy version of M-theory) via a dimensional reduction.^[2]^[3]

The content of the massless sector of the theory (which is relevant in the low energy limit) is given by ${\textstyle (8_{v}\oplus 8_{s})\otimes (8_{v}\oplus 8_{c})}$ representation of SO(8) where $8_{v}$ is the irreducible vector representation, $8_{c}$ and $8_{s}$ are the irreducible representations with odd and even eigenvalues of the fermionic parity operator often called co-spinor and spinor representations.^[4]^[5]^[6] These three representations enjoy a triality symmetry which is evident from its Dynkin diagram. The four sectors of the massless spectrum after GSO projection and decomposition into irreducible representations are ^[2]^[3]^[6]

${\text{NS-NS}}:~8_{v}\otimes 8_{v}=1\oplus 28\oplus 35=\Phi \oplus B_{\mu \nu }\oplus G_{\mu \nu }$

${\text{NS-R}}:8_{v}\otimes 8_{c}=8_{s}\oplus 56_{c}=\lambda ^{+}\oplus \psi _{m}^{-}$

${\text{R-NS}}:8_{c}\otimes 8_{s}=8_{s}\oplus 56_{s}=\lambda ^{-}\oplus \psi _{m}^{+}$

${\text{R-R}}:8_{s}\otimes 8_{c}=8_{v}\oplus 56_{t}=C_{n}\oplus C_{nmp}$

where ${\text{R}}$ and ${\text{NS}}$ stands for Ramond and Neveu-Schwarz sectors respectively. The numbers denote the dimension of the irreducible representation and equivalently the number of components of the corresponding fields. The various massless fields obtained are the graviton $G_{\mu \nu }$ with two superpartner gravitinos $\psi _{m}^{\pm }$ which gives rise to local spacetime supersymmetry,^[3] a scalar dilaton $\Phi$ with two superpartner spinors—the dilatinos $\lambda ^{\pm }$ , a 2-form spin-2 gauge field $B_{\mu \nu }$ often called the Kalb-Ramond field, a 1-form $C_{n}$ and a 3-form $C_{nmp}$ . Since the ${\text{p}}$ -form gauge fields naturally couple to extended objects with ${\text{p+1}}$ dimensional world-volume, Type II-A string theory naturally incorporates various extended objects like D0, D2, D4 and D6 branes (using Hodge duality) among the D-branes (which are ${\text{R}}$ ${\text{R}}$ charged) and F1 string and NS5 brane among other objects.^[3]^[7]^[6]

The mathematical treatment of type IIA string theory belongs to symplectic topology and algebraic geometry, particularly Gromov–Witten invariants.

Type IIB string theory

At low energies, type IIB string theory is described by type IIB supergravity in ten dimensions which is a chiral theory (left–right asymmetric) with (2,0) d=10 supersymmetry; the fact that the anomalies in this theory cancel is therefore nontrivial.

In the 1990s it was realized that type IIB string theory with the string coupling constant g is equivalent to the same theory with the coupling 1/g. This equivalence is known as S-duality.

Orientifold of type IIB string theory leads to type I string theory.

The mathematical treatment of type IIB string theory belongs to algebraic geometry, specifically the deformation theory of complex structures originally studied by Kunihiko Kodaira and Donald C. Spencer.

In 1997 Juan Maldacena gave some arguments indicating that type IIB string theory is equivalent to N = 4 supersymmetric Yang–Mills theory in the 't Hooft limit; it was the first suggestion concerning the AdS/CFT correspondence.^[8]

Relationship between the type II theories

In the late 1980s, it was realized that type IIA string theory is related to type IIB string theory by T-duality.

References

^ Duff, Michael (1998). "The theory formerly known as strings". Scientific American. 278 (2): 64–9. Bibcode:1998SciAm.278b..64D. doi:10.1038/scientificamerican0298-64.
^ ^a ^b Huq, M; Namazie, M A (1985-05-01). "Kaluza-Klein supergravity in ten dimensions". Classical and Quantum Gravity. 2 (3): 293–308. Bibcode:1985CQGra...2..293H. doi:10.1088/0264-9381/2/3/007. ISSN 0264-9381. S2CID 250879278.
^ ^a ^b ^c ^d Polchinski, Joseph (2005). String Theory: Volume 2, Superstring Theory and Beyond (Illustrated ed.). Cambridge University Press. p. 85. ISBN 978-1551439761.
^ Maccaferri, Carlo; Marino, Fabio; Valsesia, Beniamino (2023). "Introduction to String Theory". arXiv:2311.18111 [hep-th].
^ Pal, Palash Baran (2019). A Physicist's Introduction to Algebraic Structures (1st ed.). Cambridge University Press. p. 444. ISBN 978-1-108-72911-6.
^ ^a ^b ^c Nawata; Tao; Yokoyama (2022). "Fudan lectures on string theory". arXiv:2208.05179 [hep-th].
^ Ibáñez, Luis E.; Uranga, Angel M. (2012). String Theory and Particle Physics: An Introduction to String Phenomenology. Cambridge: Cambridge University Press. ISBN 978-0-521-51752-2.
^ Maldacena, Juan M. (1999). "The Large N Limit of Superconformal Field Theories and Supergravity". International Journal of Theoretical Physics. 38 (4): 1113–1133. arXiv:hep-th/9711200. Bibcode:1999IJTP...38.1113M. doi:10.1023/A:1026654312961. S2CID 12613310.

v t e String theory
Background	Strings Cosmic strings History of string theory First superstring revolution Second superstring revolution String theory landscape
Theory	Nambu–Goto action Polyakov action Bosonic string theory Superstring theory Type I string Type II string Type IIA string Type IIB string Heterotic string N=2 superstring F-theory String field theory Matrix string theory Non-critical string theory Non-linear sigma model Tachyon condensation RNS formalism GS formalism
String duality	T-duality S-duality U-duality Montonen–Olive duality
Particles and fields	Graviton Dilaton Tachyon Ramond–Ramond field Kalb–Ramond field Magnetic monopole Dual graviton Dual photon
Branes	D-brane NS5-brane M2-brane M5-brane S-brane Black brane Black holes Black string Brane cosmology Quiver diagram Hanany–Witten transition
Conformal field theory	Virasoro algebra Mirror symmetry Conformal anomaly Conformal algebra Superconformal algebra Vertex operator algebra Loop algebra Kac–Moody algebra Wess–Zumino–Witten model
Gauge theory	Anomalies Instantons Chern–Simons form Bogomol'nyi–Prasad–Sommerfield bound Exceptional Lie groups (G₂, F₄, E₆, E₇, E₈) ADE classification Dirac string p-form electrodynamics
Geometry	Worldsheet Kaluza–Klein theory Compactification Why 10 dimensions? Kähler manifold Ricci-flat manifold Calabi–Yau manifold Hyperkähler manifold K3 surface G₂ manifold Spin(7)-manifold Generalized complex manifold Orbifold Conifold Orientifold Moduli space Hořava–Witten theory K-theory (physics) Twisted K-theory
Supersymmetry	Supergravity Superspace Lie superalgebra Lie supergroup
Holography	Holographic principle AdS/CFT correspondence
M-theory	Matrix theory Introduction to M-theory
String theorists	Aganagić Arkani-Hamed Atiyah Banks Berenstein Bousso Curtright Dijkgraaf Distler Douglas Duff Dvali Ferrara Fischler Friedan Gates Gliozzi Gopakumar Green Greene Gross Gubser Gukov Guth Hanson Harvey 't Hooft Hořava Gibbons Kachru Kaku Kallosh Kaluza Kapustin Klebanov Knizhnik Kontsevich Klein Linde Maldacena Mandelstam Marolf Martinec Minwalla Moore Motl Mukhi Myers Nanopoulos Năstase Nekrasov Neveu Nielsen van Nieuwenhuizen Novikov Olive Ooguri Ovrut Polchinski Polyakov Rajaraman Ramond Randall Randjbar-Daemi Roček Rohm Sagnotti Scherk Schwarz Seiberg Sen Shenker Siegel Silverstein Sơn Staudacher Steinhardt Strominger Sundrum Susskind Townsend Trivedi Turok Vafa Veneziano Verlinde Verlinde Wess Witten Yau Yoneya Zamolodchikov Zamolodchikov Zaslow Zumino Zwiebach

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