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Arkani-Hamed: “Dark Forces, Smoking Guns, and Lepton Jets at the LHC” December 11, 2008

Posted by dorigo in news, physics, science.
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As we’ve been waiting for the LHC to turn on and turn the world upside down, some interesting data has been coming out of astrophysics, and a lot of striking new signals could show up. This motivates theoretical investigations on the origins of dark matter and related issues, particularly in the field of Supersymmetry.

Nima said he wanted to tell the story from the top-down approach: what all the
anomalies were, what motivated his and his colleagues’ work. But instead, he offered a parable as a starter.

Imagine there are creatures made of dark matter: ok, dark matter does not clump, but anyway, leaving disbelief aside, let’s imagine there are these dark astrophysicists, who work hard, make measurements, and eventually see that 4% of the universe dark to them, they can’t explain the matter budget of the universe. So they try to figure out what’s missing. A theorist comes out with a good idea: a single neutral fermion. This is quite economical, and this theory surely receives a lot of subscribers. But another theorist envisions that there is a totally unknown gauge theory, with a broken SU(2)xU(1) group, three generations of fermions, the whole shebang… It seems crazy, but this guy has the right answer!

So, we really do not know what’s in the dark sector. It could be more interesting than just a single neutral particle. Since this is going to be a top-down discussion, let us imagine the next most complicated thing you might imagine: Dark matter could be charged. If the gauge symmetry was exact, there would be some degenerate gauge bosons. How does this stuff have contact with the standard model ?

Let us take a mass of a TeV: everything is normal about it, and the coupling that stuff from this dark U(1) group can have is a kinetic mixing between our SM ones and these new gauge fields, a term of the form 1/2 \epsilon F_{\mu \nu}^{dark} F^{\mu \nu} in the Lagrangian density.

In general, any particle at any mass scale will induce a loop mixing through their hypercharge above the weak scale. All SM particles get a tiny charge under the new U(1)’. The coupling can be written as kinetic mixing term, and it will be proportional to their electric charge. The size of the coupling could be in the 10^-3, 10^-4 range.

This construct would mess up our picture of dark matter, and a lot about our
cosmology. But if there are higgses under this sector, we have the usual problem of hierarchy. We know the simplest solution to the hierarchy is SUSY. So we imagine to supersymmetrize the whole thing. There is then a MSSM in our sector, and a whole SUSY dark sector. Then there is a tiny kinetic mixing between the two. If the mixing is 10^-3, from the breaking of symmetry at a mass scale of about 100 GeV, the breaking induced in the DM world would be of radiative origin, through loop diagrams, at a few GeV mass scale.

So the gauge interaction in the DM sector is broken at the Gev scale. A bunch
of vectors, and other particles, right next door. Particles would couple
to SM ones proportionally to charge at levels of 10^-3 – 10^-4. This is dangerous since the suppression is not large. The best limits to such a scenario come from e+e- factories. It is really interesting to go back and look at these things in BaBar and other experiments: existing data on tape. We might discover something there!

All the cosmological inputs have difficulty with the standard WIMP scenario. DAMA, Pamela, Atic are recently evidenced anomalies that do not fit with our
simplest-minded picture. But they get framed nicely in our picture instead.

The scale of these new particles is more or less fixed at the GeV region. This has an impact in every way that you look at DM. As for the spectrum of the theory, there is a splitting in masses, given by the coupling constant \alpha in the DM sector times the mass in the DM sector: a scale of the order \alpha M.  It is radiative. There are thus MeV-like splittings between the states. And there are new bosons with GeV masses that couple to them. These vectors couple off-diagonally to the DM. This is a crucial fact, sinply because if you have N states, their gauge interaction is a subpart of a rotation between them. The only possible interaction that these particles can have with the vector is off-diagonal. That gives a cross section comparable to the weak scale.

The particles annihilate into the new vectors, which eventually have to decay. They would be stable, but there is a non-zero coupling to our world, so what do they decay into ? Not to proton-antiproton pairs, but electrons, or muon pairs. These features are things that are hard to get with ordinary WIMPS.

And there is something else to expect: these particles move slowly, have long range interaction, geometric cross sections, and they may go into excited states. Their splitting is of the order of the MeV, which is not different from the kinetic energy in the galaxy. So with the big geometric cross section they have, you expect them not to annihilate but excite. They decay back by emitting e+e- pairs. So that’s a source of low-energy e- and e+: that explains an integral excess in these particles from cosmic rays.

If they hit a nucleus, the nucleus has a charge, the vector is light, and thus the cross section is comparable to Z and H exchange. So the collision is not elastic, it changes the nature of the particle. This changes the analysis you would do, and it is possible for DAMA to be consistent with the other experiments.

Of course, the picture drawn above is not the most minimal possible thing, to
imagine that dark matter is charged and has gauge interactions is a quite far-fetched thing in fact. But it can give you a correlated explanation to the cosmological inputs.

Now, why does this have the potential of making life so good at the LHC ? Because we can actually probe this sector sitting next door, particularly in the SUSY picture. In fact, SUSY fits nicely in the picture, while being motivated elsewhere.

This new “hidden” sector has been studied by Strassler and friends in Hidden valley models. It is the leading way by means of which you can have a gauge sector talking to our standard model.

The particular sort of hidden valley model we have discussed is motivated if you take the hints from astrophysics seriously. Now what does it do to the LHC ? GeV particles unseen for thirty years….  But that is because we have to pay a price, the tiny mixing.

Now, what happens with SUSY is nice: if you produce superpartners you will always go into this sector. The reason is simple: normally particles decay into the LSP, which is stable. But now it cannot be stable any longer, because the coupling will give a mixing between gaugino in our sector and photino in their sector. Thus, the LSP will decay to lighter particle in the other sector, producing other particles. These particles are light, so they come out very boosted. They make a Higgs boson in the other sector, which decays to a W pair, and finally ends up with the lightest vector in the other sector: it ends up as an electron-positron pair in this sector.

There is a whole set of decays that gives lots of leptons, all soft in their sector. They are coming from the decay of a 100 GeV particle. The signature could be jets of leptons. Every SUSY event will contain two. Two jets of leptons, with at least two, if not many more, leptons with high-Pt, but featuring small opening angles and invariant masses. That is the smoking gun. As for lifetime, these leptons are typically prompt, but they might also have a lifetime. However the preferred situation is that they would not be displaced, they would be typically prompt.


1. Matti Pitkänen - December 12, 2008

Amusing, just this is what I have been talking for years but in much more elegant form and in much more detail with applications ranging from quantum Hall effect to astrophysics to cosmology to quantum biology.

Much of honor goes to Nottale who noticed that inner and outer planetary orbits can be seen as Bohr orbits with a gigantic value of Planck constant. The TGD explanation is in terms of condensation of visible matter at 2-D surfaces defining anyonic systems consisting of dark matter with very large Planck constant and therefore in macroscopically quantum coherent phase. This would be the basic mechanism for the formation of planetary systems (see my blog).

This finding and various biological anomalies led to the generalization of 8-D imbedding space of TGD having a book like structure with pages labeled by different values of Planck constant (this is oversimplification), and containing space-times as 4-surfaces. Typically the light-like 3-surfaces – the basic objects of TGD Universe- are at one particular page but tunneling is possible by leakage through the back of the book.

We would live at one particular page and the matter at other pages would be dark relative to us. It can be just ordinary particles if stability conditions allow this (anyonic phase is highly suggestive). There are no local interaction vertices between particles belonging to different pages. This explains darkness.

Particles can leak between different pages and it is even possible to photograph dark matter. This provides a possible explanation for various strange findings of Peter Gariaev about interaction of DNA with visible, IR and UV light. There is long list of other anomalies in living matter finding explanation in this framework. In living matter this kind of interactions would take place routinely in the model of quantum biology based on dark matter. One fascinating implication is phase transition changing the value of Planck constant and scaling up or down quantum scales typically proportional to hbar: this provides fundamental control mechanism of cellular biology where phase transition change the size scale occur very frequently.

About CDF anomaly and related anomalies. TGD predicts both leptons and quarks have colored excitations. Color octet excitations of leptons plus p-adic length scale hypothesis explains quantitatively CDF anomaly (predicts the mass of lightest excitation (charged tau-pion with mass mtau), the masses of the excitations proposed by CDF come as 2*mtau, 4*mtau, 8*mtau (neutral tau-pions) in accordance with the proposal of CDF group. Model also provides mechanism producing the muon jets and predicts a correct order of magnitude for the production cross section. Also very importantly, if colored excitations of leptons are present only at pages having nonstandard Planck constant, there is no contribution to intermediate boson decay widths from decays to colored leptons.

During years many other similar anomalies have been found. Electropions made themselves visible already at seventies in heavy ion collisions. About this I published two papers in International Journal of Theoretical Physics (1990,1992). Ortopositronium decay rate anomaly has interpretation in terms of electropion. The gamma rays with energies at electron rest mass from galactic nuclei have interpretation as decay products of dark electro-pions. I have also discussed Karmen anomaly as the first evidence for colored excitations of muon. Year ago emerged evidence for mu-pion.

This approach to dark matter differs from Nima’s in three respects. It came three years earlier (as becomes clear by looking at old postings in my blog and links to the books and articles at my home page, there are also publications in CASYS proceedings). It is much more elegant since just the standard model gauge group is postulated (actually this gauge group follows as a prediction from number theoretic vision about TGD). And it implies a profound generalization of quantum theory itself.

This theory is however crackpot theory according to the crowd opinion. Dear Anonymous, before telling me not to fill this blog with spam, tell me exactly what makes TGD a crackpot theory. If you bother to go to my
home page
and read you find that it cannot be the content. What it is then? I am really interested. Perhaps also some others are.

Note that the URL of my home page has changed since few weeks after the discovery of CDF anomaly Helsinki University informed me that the old URL is not available after 10.12. With the help of some friendly souls the date was changed to 31.12. Otherwise TGD had disappeared from the web totally since for some reason they are unable to redirect visitors to the new URL after the page has been removed.

dorigo - December 13, 2008

Hi Matti,

crackpot or not, I do not mind if you advertise your theory here. However, as you know I do not feel qualified to discuss it… Thanks for commenting, anyway.


2. estraven - December 12, 2008

“Nima has impressive dark eyes, and he gives a natural impression of authority despite being rather young. He is lean, not tall, with long black hair falling on his shouders; he is slightly balding on the top of his head, but he looks attractive and fit.”

The Gender and Sexual Orientation Parity Committeee politely requests a picture.

dorigo - December 13, 2008

Estraven, that’s right – I should have taken a pic. I think I’ll look for one in the web.

3. Andrea Giammanco - December 12, 2008

Thanks for this transcript, this is really inspiring.

dorigo - December 13, 2008

UW andrea,


4. Ervin Goldfain - December 13, 2008

Dear Dr. Dorigo,

Thank you for this informative post. Here is a down-to-earth question: what objective evidence there is to hint that anomalous phenomena Nina is talking about come from the Dark Matter sector? Isn’t he jumping the gun in making speculative assumptions? What if physics of far-from-equilibrium phenomena provides a more natural explanation that bypasses Dark Matter?



dorigo - December 13, 2008

Dear Ervin,

I can see no direct evidence for dark matter in the present data, although one might interpret that way some of the anomalies. Of course, DM is a very outstanding question, and we have the detection capabilities to expect to see it in our data any time – if it is there. This biases minds favourably.

I have no idea what non-equilibrium phenomena you are thinking at. In any case, I think the case is still open for other explanations to the many anomalies Nima discussed.


5. Guess Who - December 13, 2008
6. Ervin Goldfain - December 13, 2008

Dear Dr. Dorigo,

Far-from-equilibrium phenomena I aluded to refer to the behavior of a large class of systems that fall outside the postulates of Boltzmann-Gibbs statistics and conventional QFT. These phenomena are known to violate unitarity, locality and the fluctuation-dissipation theorem. There are preliminary indications that non-equilibrium phase transitions may be the driver in some deep inelastic scattering processes, the physics of TeV sector and gamma ray bursts, formation of quark-gluon plasma in heavy ion collisions and the physics of inflation.

7. Codger - December 15, 2008

Dear Guess Who:

Thank you for posting that photo. I can now poke out my eyes with a clear conscience.

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