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More on fine tuning, and Occam’s razor December 1, 2006

Posted by dorigo in personal, physics, science.

Andrea Romanino, the speaker at the Atlas-CMS workshop I reported on last week, left an interesting comment on my post “Fine tuning and new physics at the LHC”. I think it worthwhile to post it here by itself… 

“I am glad my talk rised some interest and I would like to take this opportunity to further clarify the argument reported above.

People often ask whether the few percent fine-tuning present e.g. the MSSM should be taken seriously. I do not know the answer, but it is fair to say that the belief that new physics will show up at the LHC is based on this very type of fine-tuning argument: ‘new physics must show up at the LHC, or else a light Higgs would require a significant fine-tuning’. To be concrete, a permille tuning would allow the sparticles of the MSSM to be out of reach at LHC.

Of course percent is quite different from permille: the percent problem might indeed be irrelevant and the sparticles of the most traditional MSSM version might very well lay in that one order of magnitude separating percent from permille. However, I would not neglect the possibility that the little percent problem be an indication that we should expect a departure from the MinimalSSM.

That is why I believe not only that the LHC will be a success, but also that surprises are not excluded. A slightly non-MinimalSSM, or wilder alternatives perhaps, we will see.”

My own pitch on the whole thing ? Occam’s Razor allows me to believe in the Higgs, because it explains a lot of things with the smallest effort. Sure, it does not explain everything. But if, having accepted the Higgs, I find myself having to bargain a whole lot of new entities to make the Higgs mechanism cleaner (i.e. no fine tuning necessary), then I throw my hands up and declare I stop at the SM Higgs for now. If then I not only have to buy the MSSM, but even go further, I tend to “reach for my gun”, to paraphrase Stephen Hawking… Let’s find that one thing first, then maybe the Razor will not come slashing fancier models…


1. An update on the 2.1-sigma MSSM Higgs signal « A Quantum Diaries Survivor - May 29, 2008

[…] of the Standard Model (which was excellently explained by Michelangelo Mangano recently; also see Andrea Romanino’s perspective on the issue), and it would have the added benefit of allowing a unification of coupling constants […]

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