Saturday, 13 January 2007

Csaba Csaki and new directions for gauge mediation

Csaba Csaki from Cornell is visiting CERN TH these days. Last week he gave a talk entitled Direct gauge mediation from metastable vacua. The first part of the talk was a very nice review of dynamical supersymmetry breaking, including the recent work by Intriligator, Seiberg and Shih (ISS) concerning supersymmetry breaking in metastable vacua. The second part was a less nice presentation of his model of gauge mediation based on the ISS idea.

Dynamical supersymmetry breaking is an attractive idea, which is however hard to implement in realistic models. One of the obstacles is that in simple (non-chiral) theories, like SUSY QCD, the true vacuum is supersymmetric. Recently, ISS noticed that SUSY QCD can have metastable supersymmetry breaking vacua whose lifetime is long enough for practical purposes. This observation raised hopes that realistic models involving dynamical supersymmetry breaking could be greatly simplified. A lot theoretical activity followed (more than 50 citations of ISS in less than one year). The model of Csaba and collaborators is an attempt to get on this train.

In gauge mediation we need messengers: the fields coupled directly to the supersymmetry breaking sector and also to the visible sector, via the Standard Model gauge interactions.
The messengers communicate supersymmetry breaking to the visible sector and generate an acceptable pattern of soft breaking terms. Typically, this link between the hidden and observable sectors is yet another sector, distinct from the other two. The main idea of Csaba is to make the messengers a part of the susy breaking dynamics. He succeeds, but his fully realistic model is quite involved. It is easy to gauge an SU(5) subgroup (the unified group including the Standard Model) of the ISS-type SU(N) model (SU(6) in the Csaba's paper). Then some of the composite mesons may act as messengers. But one also needs to break the residual R-symmetry of the ISS model to generate the MSSM gaugino masses , so let's add four singlets...and then it goes downhill.

We all know it well from our own experience ;-) We start with a fine idea that needs just small amendments to become realistic. After some time we are too deep in the forest to find our way back home.

A more interesting model in the similar spirit seems to be that of Murayama and Nomura .
It is a less ambitious attempt (the messenger sector is still ad-hoc), but thanks to the ISS idea they get rid of the R-symmetry, that is always a pain in dynamical susy breaking. Anyway, it seems that there is still some room for progress here.

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