Wednesday 7 December 2011

The MSSM (sort of) from the heterotic string

Today I have a new paper out with several collaborators, in which we construct compactifications of the heterotic string which lead to exactly the light field content of the MSSM in four dimensions. In itself, this is not a new achievement; it has been about six years since such models first appeared in the literature. The difference is that these models are obtained by deformations of the so-called 'standard embedding' solution.

Although you probably either know this already, or won't understand it without a lot more background, let me briefly explain what this means. In 1985, a seminal paper (of which Philip Candelas, one of my collaborators on the new work, was a co-author) established that there is a canonical way to compactify the $E_8{\times}E_8$ heterotic string theory on any Calabi-Yau threefold $X$, leading to an $\mathcal{N}=1$ supersymmetric theory in flat four-dimensional spacetime. More specifically, it yields an $E_6$ gauge theory, with matter content determined by the topology of the manifold — there are $h^{2,1}(X)$ ($h^{1,1}(X)$) chiral multiplets in the $\mathbf{27}$ ($\mathbf{\overline{27}}$) representation, where the notation $h^{p,q}(X)$ refers to the Hodge numbers of $X$.

There are lots of problems with the standard embedding as I've described it so far:

Friday 2 December 2011

The status of the Higgs boson in 2011

The Higgs boson is the last piece of the Standard Model of particle physics which has yet to be verified by experiment. As everybody knows, discovering this particle (or perhaps ruling out its existence) is one of the primary goals of the LHC.

Last month, the two big collaborations focussed on discovery of new particles at the LHC — the ATLAS and CMS teams — released combined results from their searches for the Higgs; the punchline is the following plot:

If you don't understand these "Brazil band" plots, I refer you to a blog entry by Tommaso Dorigo (I actually stole the picture from another of his blog posts; I hope he doesn't mind). Roughly speaking though, we conclude that the Higgs does not exist at mass values where the data falls below the red line.