|All Roads Lead to String Theory (Polchinski)|
Prior to the First Superstring Revolution
|Early History|| S-Matrix Theory|
|Bosonic String Theory|| Worldsheet|
Bosonic String Theory
String Perturbation Theory
|Supersymmetric Revolution|| Supersymmetry|
|First Superstring Revolution|| GSO Projection|
Type II String Theory
Type IIB String Theory
Type IIA String Theory
Type I String Theory
Type H String Theory
Type HO String Theory
Type HE String Theory
|Second Superstring Revolution|| T-Duality|
Horava-Witten String Theory
N=4 Super-Yang-Mills Theory
BFSS Matrix Theory
Matrix String Theory
Twistor String Theory
String Field Theory
Pure Spinor Formalism
After the Revolutions
|Phenomenology|| String Theory Landscape|
Minimal Supersymmetric Standard Model
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In String Theory, Type I String Theory is one of five consistent Supersymmetryic String Theories in ten dimensions. It is the only one whose strings are unoriented (both orientations of a string are equivalent) and which contains not only Closed Strings, but also Open Strings.
The classic 1976 work of Ferdinando Gliozzi, Joel Scherk and David Olive paved the way to a systematic understanding of the rules behind string spectra in cases where only Closed Strings are present via Modular Invariance but did not immediately lead to similar progress for models with Open Strings.
As first proposed by Augusto Sagnotti in 1987, the Type I String Theory can be obtained as an Orientifold of Type IIB String Theory, with 32 half-D9-Branes added in the vacuum to cancel various anamolyies, along with an extra Open String sector.
At low energies, Type I String Theory is described by the Supergravity (Type I Supergravity) in ten dimensions.. The discovery in 1984 by Michael Green and John H. Schwarz that anomalies in Type I String Theory cancel was a key reason for the First Superstring Revolution.. However, a key property of these models, shown by Augosto Sagnotti in 1992, is that in general the Green-Schwarz mechanism takes a more general form, and involves several two forms in the cancellation mechanism.
The relation (Orientifold Projection) between the Type IIB String Theory and the Type I String Theory has a large number of surprising consequences, both in ten and in lower dimensions, that were first displayed by the String Theory group at the University of Rome "Tor Vergata" in the early Nineties.  It opened the way to the construction of entire new classes of string spectra with or without Supersymmetry. Joseph Polchinski's work on D-Branes provided a geometrical interpretation for these results in terms of extended objects (D-Brane, Orientifold). 
In the 1990s it was first argued by Edward Witten that Type I String Theory with the string coupling constant is equivalent to the Type HO String Theory with the coupling .  This equivalence is known as S-Duality. . . . .
Action PrincipleEdit this section
The Action is then given by:
Projection of statesEdit this section
- 1. The GSO Projection is the same as in Type IIB String Theory. For the Neveu-Schwarz Neveu-Schwarz sector, it is, :
For the Ramond Ramond sector, it can either be: 
- Or it could be: the following: projection: : 
For the Ramond Neveu-Schwarz and the Neveu-Schwarz sectors, one may apply the Neveu-Schwarz sector GSO Projection on the Neveu-Schwarz component of the state and any of the Ramond sector GSO Projection on the Ramond component of the State. 
- 2. The Orientifold Projection needs to be applied on to the RNS states . This is just another way of saying that only those states which are invariant under Worldsheet parity are taken. This is because, since the string should be unoriented, that just means that even if you flip the string in the other direction, it should look pretty much the same. And since the Worldsheet is just a smear of the String through time, and since the string should alwaysk be unoriented, the Worldsheet should also be "unoriented" in the spatial direction. In other words, the theory should be invariant under Worldsheet parity. 
For the Open strings, the same GSO Projection applies, but there is no Orientifold projection as there is no Type IIB String Theory with open strings at all!. Instead, one simply takes the GSO Projection of the RNS Open string states and then, plonks them in. 
Orientifold projection of statesEdit this section
ReferencesEdit this section
- ↑ F. Gliozzi, J. Scherk and D.I. Olive, ``Supersymmetry, Supergravity Theories And The Dual Spinor Model, Nucl. Phys. B122 (1977) 253.
- ↑ . Angelantonj and A. Sagnotti, ``Open strings, Phys. Rept. 1 [Erratum-ibid. ) 339] [arXiv:hep-th/0204089].
- ↑ 3.0 3.1 J. Polchinski, S. Chaudhuri and C.V. Johnson, ``Notes on D-Branes, arXiv:hep-th/9602052.
- ↑ E. Witten, ``String theory dynamics in various dimensions, Nucl. Phys. B443 (1995) 85 [arXiv:hep-th/9503124].
- ↑ McMohan, David (2009). String theory DeMystified. Chicago: McGrawHill. ISBN 978-0071498708. http://www.nucleares.unam.mx/~alberto/apuntes/mcmahon.pdf.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 Mohaupt, Thomas. Introduction to String theory. http://arxiv.org/pdf/hep-th/0207249v1.pdf.
NotesEdit this section
- E. Witten, ``String theory dynamics in various dimensions, Nucl. Phys. B443 (1995) 85 [arXiv:hep-th/9503124].
- J. Polchinski, S. Chaudhuri and C.V. Johnson, ``Notes on D-Branes, arXiv:hep-th/9602052.
- C. Angelantonj and A. Sagnotti, ``Open strings, Phys. Rept. 1 [Erratum-ibid. ) 339] [arXiv:hep-th/0204089].