## Monday, November 19, 2007

### Type IIA vacua claimed to be cosmologically excluded

Take Barton Zwiebach's textbook on string theory and read his story about the type IIA braneworld scenarios with intersecting D6-branes. They surely look beautiful as a possible source of the Standard Model but are they correct?
Hertzberg, Kachru, Taylor, Tegmark
claim that they can rule out all types of type IIA models that have been constructed in literature, by their violation of cosmological requirements.

The slow-roll parameter epsilon that should be small is shown to be greater than 27/13 whenever the potential V is positive. You may view this inequality as a quantitative example of our generalized "weak gravity" principle. Slow-roll inflation and de Sitter vacua therefore become impossible. Their theorem makes some assumptions - such as the absence of NS5-branes. They sketch a possible class of models with extra features that could circumvent their no-go theorem. Well, with the right ingredients to obtain mirrors of the type IIB vacua claimed to be alive and well, it should be possible. ;-)

Sociologically speaking, you may want to know that these authors have been saying that type IIB vacua - the canonical KKLT-like and KKLLMT-like landscape - are the phenomenologically more acceptable ones for quite some time.