Nathan Seiberg is no longer working on string theory, and is now working full time on LHC related physics. He considers supersymmetry to be the most conservative possibility for physics to be discovered in the LHC, and also the most concrete. In terms of making predictions, he says that “nothing else comes close”.
He gave an excellent clear talk on ‘Gauge mediation of SUSY breaking’, a topic which is of particular interest for those (like myself) interested in LHC phenomenology.
He summarized on the order of 10,000 papers on SUSY in one slide! The mechanism for supersymmetry breaking consists of coupling a ‘hidden sector’ where supersymmetry is broken, to the minimal supersymmetric standard model (MSSM) via some kind of mediator particles.
He talked about two different possible kinds of mediation – gauge mediation and gravity mediation. The latter is a more speculative theory, involving complicated Plank suppressed operators, whereas the former is more predictive and the mediators are governed by the standard model gauge interactions, so they couple to both our good old SM fermions (photons, gluons, etc.), and to particles in a hidden sector. This is the method of mediation that he focused on for the rest of the talk. The hidden sector includes the SUSY breaking sector, other particles that are beyond the standard model and messenger particles, if they exist.
In trying to finding common predictions of the thousands of different gauge mediated theories available, Seiberg presented original work done by himself, Meade and Shih to find general predictions of these gauge mediated theories. Assume that the hidden sector has some global symmetry G (e.g.- it could be U(1) symmetry, giving these hidden sector particles electric charge). Then Noether’s theorem tells us there is a conserved current corresponding to this symmetry, and it is the correlation functions of this current that encode all the hidden sector information. Seiberg et al. then derive identities that hold in general for this class of theories. They make generic predictions for all gauge mediated theories, as well as some predictions specific to simple models with messengers. Thus they have provided a model independent set of predictions for gauge mediated theories that could potentially be detected at the LHC.