## Tuesday, April 15, 2008 ... //

### The High Country in the landscape

Bouchard and Donagi have a new and interesting paper about the heterotic string phenomenology. They explain that it is important to impose all major constraints on heterotic models.

In other words, they define the High Country region of the landscape ;-) where the vacua have the MSSM spectrum and satisfy some additional constraints. It seems that they insist that they still know exactly one compactification from 2005 only that obeys all the requirements. Note that more than two years ago, they wrote on page 1 that they didn't claim that it was the model of the Universe but it was the best model they had; this sentence was followed by a smiling, a rather rare creature in Phys Lett B papers. :-)

If it is the best model we can possibly have, the sentence and the smiling may become legendary. ;-)

As their paper shows, a weakening of the constraints inevitably leads to a gigantic (and perhaps infinite) expansion of the phenomenologically or theoretically not-quite-acceptable possibilities. In other words, the landscape is only large until you begin to do what every honest scientist must do - namely to discriminate. If you want to know one more detail, they eliminate the model by Braun et al. (widely covered on this blog) that needed anti-M5-branes, besides M5-branes, to fight against anomalies (or poly-instability) because it ended up as a non-supersymmetric model that might be on par with the gadzillion of partly sick, non-High-Country models that they present.

They also sketch a new project to classify Calabi-Yau compactifications with Z6 Wilson lines.

Membrane minirevolution

Meanwhile, the membrane minirevolution seems to escalate. Today, there are three new papers about the Bagger-Lambert-Gustavsson theory. With this growth rate, the topic could soon exceed the AdS/CFT correspondence. ;-)

Ho, Hou, Matsuo claim to have some new Lie 3-algebras. They can construct their tensor product representations, too.

Gomis, Salin, Passerini emphasize an obvious fact that the new 3-algebra Lagrangian (compactified on a two-torus) can be directly used for the DLCQ, Matrix-theoretical description of type IIB string theory. In order to say something non-trivial, they also write down the pp-wave deformation of this theory.

Finally, Bergshoeff, de Roo, Hohm rewrite the Lagrangian in terms of scalars, instead of tensors, to describe the embedding. The resulting formulation makes the parity symmetry more manifest. Their rewriting follows a similar trick that is used in gauged supergravities.