Monday, September 24, 2007

M-Theory Through the Looking Glass


















A new paper by Horava and Keeler came out a few days ago, with the whimsical title M-Theory Through the Looking Glass: Tachyon Condensation in the E_8 Heterotic String. LuboŇ° Motl gave it a thumbs up, as do I for the use of only one copy of E8. The abstract is as follows:

We study the spacetime decay to nothing in string theory and M-theory. First we recall a nonsupersymmetric version of heterotic M-theory, in which bubbles of nothing -- connecting the two E_8 boundaries by a throat -- are expected to be nucleated. We argue that the fate of this system should be addressed at weak string coupling, where the nonperturbative instanton instability is expected to turn into a perturbative tachyonic one. We identify the unique string theory that could describe this process: The heterotic model with one E_8 gauge group and a singlet tachyon. We then use worldsheet methods to study the tachyon condensation in the NSR formulation of this model, and show that it induces a worldsheet super-Higgs effect. The main theme of our analysis is the possibility of making meaningful alternative gauge choices for worldsheet supersymmetry, in place of the conventional superconformal gauge. We show in a version of unitary gauge how the worldsheet gravitino assimilates the goldstino and becomes dynamical. This picture clarifies recent results of Hellerman and Swanson. We also present analogs of R_\xi gauges, and note the importance of logarithmic CFT in the context of tachyon condensation.

Saturday, September 01, 2007

The Flying Car

Tired of being stuck in traffic?


According to the Moller website, the Skycar sits four passengers, has a maximum speed of 375 MPH, runs on ethanol (yes, ethanol Carl!) and best of all has a low-end price tag of only $500,000. ;)