fact that strings without spacetime supersymmetry are The primary reason for this relative lack ofĪttention is the. Relatively little work studying the phenomenologies associated with their Unfortunately, during this same period, there has been The rich and diverse phenomenologies of heterotic strings exhibiting spacetime Over the past three decades, considerable effort has been devoted to studying With the heterotic string, attention focussed on closed string theories, for two reasons: `phenomenology' Open string theories were believed to be `ugly', because of the lack of the power of compl Read more The original motivation was the application of string theories to strong interactions to describe mesons: a quark and an anti-quark at the two ends of a string. Historically, they are even older than closed string theories. string theories where the world sheet has boundaries, have been under investigation for a long time. Type I theories Theories of open strings, i.e. I will give a five minutes (and therefore rather superficial) overview on that. There are 3 reasons to be interested in this topics: theories of open strings (`type I') D-branes various systems with boundaries in statistical mechanics. Introduction Recently, physicists have become interested (again, but more intensely) in CFT on real twodimensional surfaces with boundaries and /or unorientable. The lower limit to string coupling unification in weakly coupled heterotic strings was shown by Kaplunovsky to be around Lambda_H ~ 5 x 10^ Z2 twist of the NAHE variation offersĪ range of mirror models not possible from NAHE-based models.
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