The landscape reputedly has ten to the one hundred or ten to the five hundred different members, each with a number of infinitely adjustable parameters. But supposedly it does not have an infinite number of members. Yang-Mills theory, on the other hand, has at least a countably infinite number of discretely different examples, e.g. SU(N) for every value of N. Why is it that String Theory does not have a similarly uncountable number of instantiations? For instance, in chapter 15 of his book, Zwiebach, constructs a representation of a theory similar to the standard model using three baryonic branes, two right branes, one left brane and one leptonic brane. Suppose one uses N baryonic branes instead of three. What makes the model fail?(adsbygoogle = window.adsbygoogle || []).push({});

Or to put it another way, which values of SU(N) can not be embedded in string theory? Is it still believed that the group must be included in E8xE8 or SO(32)?

I don’t understand either string theory, or the landscape, but this new stuff has me very confused. Once, there were only a few models. Now there are a lot, but not an infinite number.

One more example: at a recent conference, Bryan Greene showed his schematic picture of a three dimensional grid with a sphere at every intersection. At the same conference, Lenny Susskind, discussing the KLMT and KKLMTT constructions, (which he called Rube Goldberg contraptions) showed a picture that looked like a two scoop ice cream cone, only the “scoops” were tori, rather than spheres. Even forgetting the cone, which I think is supposed to represent a conifold, why doesn’t replacing Brian Greene’s sphere at every intersection an with N hole torus at every intersection lead to a countably infinite landscape?

I would be grateful to anyone who can shed some enlightenment on which simple manifold are not allowed and why not. TIA.

Jim Graber

(I have also posted this question to SPS via Google. Perhaps, after the usual lengthy moderation delays, one of the moderators might reply.)

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# Why not a countably infinite landscape?

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