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Fine tuning and new physics at the LHC November 25, 2006

Posted by dorigo in news, physics, science.

Today’s Atlas-CMS workshop featured a talk by Andrea Romanino, who gave a nice review of the physics scenarios of the LHC, and spent some time discussing the problem of fine tuning: the radiative corrections to the Higgs mass being dependent on the mass scale at which new physics is present, through some parameters that have to be “fine-tuned”, that is found to have just the right value to make the math work.

The bottomline is that if you are disturbed by fine-tuning of the theory at the level of percent or so, the new physics scale – the value of masses at which new physics could be observed – becomes too high, and thus out of reach of the LHC. Beware, this is somehow a simplification of a very complex issue, and there are independent arguments that would change the picture.

I am not sure I understood more than 50% of the talk – so please be advised that rather than asking me the details, you could directly go and look at the slides by yourself: they can be found at http://www.bo.infn.it/Atlas-Cms2006/ .

However, the flavor I tasted of the whole thing is that the more we get close to put our hands on proton collisions at 14 TeV, the more we worry about it not  being enough for letting us see beyond… The experimentalists at the talk today look to me as kids who used all their LEGO to build a step to climb on in order to reach and see what’s inside a forbidden drawer: the step looked impressive as they were assembling it, but as they drag it next to the cupboard, they wonder whether they’ll get high enough by stepping on it…


1. analysst - November 25, 2006

Sounds interesting, going to reveiw this when I get home.

2. Not Even Wrong » Blog Archive » Media and Other News - November 25, 2006

[…] Update:  For a more general discussion of the question of whether new physics that solves the naturalness problem will be visible at the LHC, see a recent posting by Tommaso Dorigo, who is reporting on a conference going on in Bologna, especially the talk by Andrea Romanino. […]

3. Andrea Romanino - November 30, 2006

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.

4. dorigo - December 1, 2006

Hi Andrea, thank you for your visit. I think your comment is interesting and will promote it to an independent post.


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