Friday, January 13, 2006

Supersymmetry breaking

I recommend everyone the review of "Supersymmetry Breaking" by Yael Shadmi that finally brings some of the secrets of anomaly-mediated supersymmetry breaking (and the relevant references) to the mortal stringy human beings - secrets that have been largerly hidden in the hep-ph archive.

The main punch line is that the anomaly-mediated supersymmetry breaking is the most beautiful way to communicate supersymmetry breaking - which must originally occur in the hidden sector (MSSM itself is not enough). It induces no flavor changing neutral currents (unlike gauge-mediated and gravity-mediated pictures) and predicts the masses of all superpartners up to an overall scale factor. All these terms arise from the scalar auxilliary field in the supergravity multiplet that breaks superconformal invariance. And the ratios of masses only depend on couplings, beta functions, and anomalous dimensions of the MSSM.

The only "small" problem with the minimal anomaly-mediated SUSY breaking (AMSB) is that it predicts tachyonic slepton (and probably squark) masses. So the minimal AMSB does not work. It can't be fixed by new physics at high scale because AMSB is highly predictive.

There are two ways to fix it:
  • using higher-order effects in "F" - the scalar auxilliary field in the SUGRA multiplet
  • adding new fields that are light before SUSY breaking
To see a recent example of the second approach, you may try a recent paper by Linda Carpenter. She only needs one new hidden U(1) - you can imagine that it comes from the M5-brane in the strongly-coupled Heterotic MSSM by Braun, He, Ovrut, and Pantev - and one parameter to be fine-tuned. No bad couplings are generated. The hep-ph arXiv has a lot of work dedicated to these issues.

Supersymmetry is beautiful, and with AMSB, it's beautiful and highly predictive even after it's broken which is why I am still proud to have made the $1,000 bet on the discovery of SUSY by summer 2008. ;-)

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