j***@mailaps.org

2005-03-29 08:12:19 UTC

Permalink

The landscape reputedly has ten to the one hundred or ten to the fiveRaw Message

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?

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 manifolds are not allowed and why not. TIA.

Jim Graber