In the morning, I read the daily papers on the arXiv and exactly one paper stayed open in my browser:Auto-Concealment of Supersymmetry in Extra Dimensions (Stanford-Oxford-Airforce Collaboration)Eminent physicist Savas Dimopoulos along with his pals (Howe, March-Russell, Scoville) argue that the LHC data don't imply that the superpartners – new elementary particles implied by supersymmetry – have to be as heavy as usually assumed. Instead, they may be rather light and such a theory yields predictions that are compatible with the LHC data – so far compatible with the Standard Model – anyway.
A possible reason why it may be hard for the collider to see SUSY is known as "compressed spectra". What does it mean? There are always some superparticles that are predicted to be produced rather often (if they're light enough). Why aren't they seen? Because they decay into products (including the lightest superpartner, the LSP, at the end) which have nearly equal masses (approximate degeneracy) which is why little energy is left for the "missing transverse energy".
And Savas et al. are proposing a clever microscopic explanation why the spectra might be compressed. Extra dimensions. They mean pretty large dimensions – much larger than the usual Planck length but much smaller than a millimeter, extra dimensions comparable to the size of a nucleus (or larger than at least 10% of a fermi, the nuclear length scale).
With such large dimensions, the momentum in the extra dimensions is "nearly continuous" which is why from the four-dimensional viewpoint, the spectrum of the new particles' masses is a discretuum, i.e. a very dense spectrum that almost resembles the continuum. With such a discretuum, pretty much any new superparticle X is rather likely to decay to a momentum mode of the LSP whose mass is just a little bit smaller than the mass of X. And the missing-energy signatures will therefore be missing. I mean suppressed or hard-to-see. Missing missing-energy signatures may sound too complex to some readers.
Generic SUSY spectra with a stop that decays to a simple LSP now require \(m_{\tilde t}\gt 700\GeV\) or so, a pretty heavy stop squark (with some other loopholes I don't want to discuss). However, with the new large extra dimensions (yes, Savas is a co-father of the the ADD large extra dimensions models), the data only imply that the stop is heavier than \(350\) or \(400\GeV\). With these extra dimensions, the LHC data don't constraint the sleptons at all.
The fundamental gravitational scale \(M_*\) is meant to be comparable to \(10\) or \(100\TeV\) – a rather natural scale "right above" the LHC, you might say, but a scale that has never been looked for in the usual searches for the extra dimensions. For example, you may be sure that the sub-millimeter gravitational experiments can't get to the nuclear distance scale. However, \(M_*\) could be as high as an intermediate scale \(M_*\sim 10^9\GeV\).
This general scenario might agree with some of the braneworlds in string theory where SUSY is broken on the non-MSSM brane(s).
Tommaso Dorigo's disrespect towards modern physics
I decided to publish this blog post when I saw Tommaso Dorigo's 11. Hide It In The Bulk. He says that according to a T-shirt, physicists who face problems because all of their other methods fail have to do one of the 10 things below:
- Manipulate the data
- Wave hands a lot, speak with a strong accent
- Invoke the Anthropic Principle
- Recall the success of the SM
- Blame it on the Planck scale
- Throw it on the lattice
- Invent another symmetry
- Set all fermion masses to zero
- Add heavy fermions
- Subtract Infinity
Well, the difficulty with Dorigo's mocking efforts is that some or many of these qualitative proposals may be right and some of them are supported by rather nontrivial evidence that they may be right. Many insights that are established by today used to be new sometime in the past – and mocked by some of the older clones of a Dorigo. Some of the models are supported by stronger evidence, some of them are supported by weaker evidence.
The T-shirt with the 10 solutions above may be funny because it combines random confused states of physicists. But if you want to interpret it seriously, it is a damn stupid mixed bag of situations that have nothing to do with each other. The manipulation with the data is usually fraud – well, in some cases, one may correct errors in the data in this way, but one must have some good luck plus other good conditions.
Waving hands and accents are just funny but they don't really carry any physics idea.
On the other hand, the anthropic principle is an idea that has been proposed to be relevant for physics and it needs to be argued about and evaluated using physical arguments that the likes of Dorigo don't even want to consider. The status of the anthropic principle is "open" at the sociological level – although I will of course tell you why all of its existing versions are wrong.
On the other hand, the success of the Standard Model and the fact that at least some differences and surprises are caused by the existence of the Planck scale – i.e. by the existence of gravity – are indisputable facts. Lattices are clearly useful and legitimate methods in physics. Well, sometimes they are useful, sometimes they are less useful; the devil is in the details. And symmetries are important principles – and every symmetry we use today was new at some moment in the past which also suggests that every symmetry that is new now has a chance to be established in the future.
Both heavy fermions and the massless limit of the fermions are important limiting situations to consider and physics can derive important qualitative implications of both assumptions. Some of these derived claims are right, some of them are wrong. Infinities have been subtracted on a daily basis for 70 or 80 years and the process works great – unless one does it incorrectly. We've known why it works so great for over 40 years, too.
Finally, things may demonstrably hide in the bulk. It is an elementary fact of any physical model that contains the "bulk" that the "bulk" has some different properties than the branes or the boundaries. Certain things are more visible in the bulk, others are less visible, and so on.
The fact that all of these eleven diverse ideas and circumstances (each of which includes hundreds of inequivalent particular claims whose truth value may differ from the rest, too!) appear on the same meant-to-be-funny shirt doesn't mean that their status is the same. It certainly doesn't mean that an intelligent person may mock all of them. Everyone who just mindlessly mocks them is a low-energy, low-brow, low-status idiot resembling Tommaso Dorigo.
Everyone who is at least 20 IQ points smarter than Tommaso Dorigo knows that there are lots of very intriguing and potentially powerful arguments in this paper – or at least many other phenomenological papers on new physics that have been written. An honest physicist simply can't ignore them. An intelligent physicist can't consider all ideas about new physics to be science-fiction.
It's bizarre when such attitudes are displayed by someone who is employed as an experimental physicist. The very purpose of the occupation is to decide which of the new ideas are right and which of them are wrong, to direct the search. It is necessary to emphasize that the experiments are not the only considerations that direct the progress. There are lots of top-down arguments that help to determine how much time competent model builders spend on one class of ideas vs another class of ideas. For example, there are lots of top-down rational reasons to think that supersymmetry gets unbroken at a high enough energy scale.
If the experimenters don't find anything new (e.g. for the next 20 years), well, we will survive. Null results also carry some information value. It's just less interesting information. I would find it surprising why people would become experimenters if they were convinced that they may discover nothing new. Maybe most students in Italy only become experimenters because they view the field as a nonsensical human activity that is actually a good welfare system where one doesn't have to do much and gets a lot.
But the people who are doing experimental physics for meritocratic reasons – who think that their work is meaningful – do share the "belief" or "world view" that some ideas will turn out to be right and they want to contribute to the separation of the right ideas from the wrong ones. To use the phrase science-fiction for all potentially good ideas is just stupidity – something utterly incompatible with the very purpose of science.
What Dorigo calls "science-fiction" is actually called "science". Papers like this new paper by Savas and pals are really science at its best. They connect some principles extracted from previous experiments and previously overlooked possibilities to find some new possibilities that were being overlooked as recently as yesterday, and extract completely well-defined (and general enough as well as particular enough) observable implications out of these assumptions. These papers map the space of possible theories and ideas and they compare this space with the real world we know from the empirical data.
There is nothing "obviously unnatural" about these ideas. Top-down arguments generally imply that "some extra dimensions" exist and their size is unknown. Near-Planckian extra dimensions may be preferred for some (mostly top-down) reasons, very large dimensions for other (mostly bottom-up) reasons, but the intermediate size isn't really ruled out and must be considered as a possibility. Such intermediate-size extra dimensions require the Standard Model on a brane and the rest of the conclusions by Savas et al. is almost guaranteed, a robust consequence of very mild assumptions.
So such papers don't really violate any "Occam's razor". They are only in conflict with the stupidity of aggressive morons such as Tommaso Dorigo who like to "cut" everything that transcends the capabilities of these marginal primates. They may use such razors every day to cut pieces of pork off their bodies. But unlike Dorigo, legitimate scientists are able to check and see that the text by Dorigo is a foul play, a stupid rant for stupid readers that doesn't contain any scientifically tolerable evidence in one way or another.
This "Occam's razor" may be good enough for Dorigos to cut many pounds of the pork off their bodies but it – mindless mocking of very serious and rather clever papers – isn't compatible with science. So: vaffanculo, Dorigo!
And that's the memo.
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