## Thursday, May 10, 2012 ... //

### Gauginos with Dirac masses and F-theory

The idea that the gauge fields of the Standard Model are extended not just to $\NNN=1$ supersymmetry multiplets but to $\NNN=2$ supermultiplets has been discussed a few times on this blog, e.g. in November 2011.

Those blog entries were mostly inspired by phenomenologists who had good enough low-energy if not low-brow reasons to add a chiral multiplet in the adjoint representation to the vector multiplets.

However, I always found such an extension very natural from a braneworld viewpoint. Gauge fields may reside on branes with rather high dimensions and they may preserve the $\NNN=2$ supersymmetry while the fermion matter multiplets only respect the $\NNN=1$ supersymmetry, being localized on intersections. This picture becomes particularly natural in F-theory, I thought, and I wondered why no string theorists discussed this scenario.

Finally, Rhys Davies, an Oxford postdoc (and infrequent physics blogger) who worked with Candelas a few years ago, published such a paper:

Dirac gauginos and unification in F-theory

He notes that the F-theory scenarios of this kind break the usual calculations suggesting the "gauge coupling unification" miracle, anyway. So it's not insane to sacrifice this old-fashioned unification by adding the new multiplets. However, he starts from scratch and tries to restore the unification.

The author concludes that with some new vector-like multiplets etc., the gauge coupling unification returns – and it occurs at the reduced Planck scale. Moreover, such a picture may become natural if the gauge fields live on a K3 cycles rather than, for example, a del Pezzo cycle which is the usual assumption in the F-theory model building.

One of the many advantages of the K3 surfaces – beyond those listed in the paper – is that I have this nice animated GIF with one of them.

#### snail feedback (1) :

reader antonio carlos motta said...

f´theory is very interesting.could to explain the exchange of particles and antiparticles and viceversa as product of the spacetime,probing that antiparticles are reversion of operator PT,that a priori is broken and renormalized through the

extended lorentz invariance or complete poincare's group