I understand Type II strings but i do not understand the difference between Type I and Type II strings. Can anyone explain this to me?

  • $\begingroup$ What about the explanations in the source where you read about them is unclear to you? Can you be more specific what you don't understand? $\endgroup$ – ACuriousMind Feb 11 '17 at 1:10
  • $\begingroup$ @ACuriousMind i have read the wikipedia article on these strings but i simply cant find the difference $\endgroup$ – anthr Feb 11 '17 at 1:13
  • $\begingroup$ Your statement of "I understand type II strings" is based on having read the rather sparse Wikipedia article? That'd call for a very different kind of answer than to someone actually trying to learn string theory from a textbook or articles. $\endgroup$ – ACuriousMind Feb 11 '17 at 1:16
  • $\begingroup$ @ACuriousMind im just asking for someone to explain it to me, if you dont want to then thats fine $\endgroup$ – anthr Feb 11 '17 at 1:17
  • $\begingroup$ The main difference is in existence of open strings in Type I. $\endgroup$ – Andrey Feldman Feb 11 '17 at 6:17

Type II superstring theory starts from the assumption that small perturbations of the vacuum state result only in orientable closed[*] strings.

By contrast, Type I superstring theory starts from the assumption that perturbations near the vacuum state can be either open or closed strings, but both must be non-orientable.

Another difference is that while Type II theories have two 10-dimensional supersymmetry generators, Type I theories have only one. This difference is a consequence of the non-orientability of Type I strings. Assuming the strings are non-orientable means forcing the positive and negative chiral components of the worldsheet spinors to be dependent on each other. They are both determined by the same set of modes, not two different sets of modes as in Type II.

For Type I superstring theory, anomaly cancellation requires the gauge group to be SO(32).

[*] Type II does include open strings. However, they don't show up in the vacuum perturbation theory--they are only there in connection with non-perturbative effects (D-branes).


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.