After 1.5 years I finally consider myself settled down and ready to return to more or less active blogging. NEQNET will be relaunched within the next 30 days with new design and hopefully lots of new content. Also, as it seems, there will be new team members working for NEQNET together with me in the position slightly more extended than that of a guest blogger. I really hope that my readers are not lost for me completely, so if you still care about NEQNET, please leave a comment to this post

If you were ever thinking about writing a guest post for NEQNET about your recent work, now is the possibility to do that. Contact me at dmitry AT nonequilibrium.net and I’ll create an account for you at NEQNET.

If you would be interested to be a co-editor at NEQNET for one (or several) of the following topics: HEP theory and string theory, HEP phenomenology, condensed matter theory, non-linear and hydrodynamics, please contact me (do the same if you feel that NEQNET should discuss some other topics, too).

Cheers,

and very respectfully yours.

Post from: NEQNET: The world of theoretical physics

Relaunching NEQNET

Dear Colleague,

we would like to inform you that as of 1st January 2010, JHEP will be published by Springer.

This agreement is based on the following key principles:

* The scientific community will remain in full control of all the scientific and editorial aspects of the Journal.
* As in the past, the subscription fee for JHEP remains as low as possible, covering no more than the actual costs of the journal and its development.
* The general financial conditions offered by Springer will allow us to pursue in the long term our aims of ensuring scientists a better compensation for their editorial and peer-review activity, and to continue to invest in research and development, thereby remaining at the very forefront of modern technologies applied to scientific publishing.
* The agreement with Springer on both subscriptions fees and open access activities adequately reflects the strategic views, anticipated market developments and willingness to explore new avenues of scientific publishing by both parties in the field of High-Energy Physics and beyond.

Best regards,

Daniele Amati
Marc Henneaux
Hector Rubinstein

Does the same fate await JCAP as well?

P.S. I have also found a fantastic site on the web which, I believe, you would enjoy – an equivalent of Abstruse Goose on the comic strip side, but also a kind of Demotivator (physics-wise). I have deeply enjoyed it, thanks, dear physicsfails.com webmaster, for making so much fun of us

Post from: NEQNET: The world of theoretical physics

JHEP is to be published by Springer

Regarding analog models I don’t have too much to report – since I am located here at relatively close vicinity to Grigory Volovik (he works in Espoo, while I work in Helsinki), I think I know the agenda quite well, and my overall impression that no so many exciting things happen on the field was confirmed on the workshop. Basically, it proves to be relatively easy to construct models of relativistic chiral fermions and vectors from non-relativistic condensed matter systems (for example, He-3). However, it seems to be impossible to construct relativistic dynamical gravity (that is, effective theory with Einstein-Hilbert action) starting from these systems – recent attempt by Horava seemed to be promising, but the ultimate answer is still the same. What we can do at most is to model a “relativistic” field theory on a curved background (such as Painleve-Gullstrand BH), but this background is static and backreaction of our field theoretic degrees of freedom on it is zero. That’s what activities on the field of analog models of gravity revolve around for almost decade.

So, let me turn to modified gravity and Nima’s talk. Since nobody in the physics blogosphere seems to really discuss the content of his talk (see Mark Trodden’s report – he attended the workshop, too), let me proudly do it for you

As you may already know, the title of the talk is “Don’t modify gravity – understand it“. Nima started by saying that he spent too much time inventing models of modified gravity and now wants to officially confess his sins.

Why? First (but not the most important as you’ll see below), because modified gravity is boring – in all (or most all) it can be reduced to usual GR + scalar field. More accurately, he has introduced the following classification: all modified gravity models can be divided into two classes -

1. boring, with subclasses a) very boring (and not excluded) and b) moderately boring (and excluded by experiments) – because of the name of the class he did not want to talk about those models at all
2. exciting. This class, according to Nima, includes only deeply flawed models such as DGP (where aforementioned scalar field possesses “Galilean invariance”) and Higgs phases of gravity (where scalar fields are essentially Goldstone modes of spontaneously broken spacetime symmetries).

So, why exciting models are deeply flawed from Nima’s point of view? The reason is the fact that, according to well-known theorem quantum gravity (based on usual GR) can not have local observables. The physical reason for that is simple. Quantum mechanics in principle allows us to measure positions of quantum particles with infinite precision (not both position and momentum though). However, measuring position with infinite precision assumes that we have an infinitely heavy apparatus to measure it. Quantum gravity in turn does not allow us to have an infinitely heavy apparatus (sufficiently heavy one would trivially turn into black hole).

A correct language for describing gravitational degrees of freedom should look more like holography. Basically, holography means non-local degrees of freedom, and non-local degrees of freedom mean holography.

Yet, non-locality of gravity will only be noticeable only if we take into account non-perturbative effects, suppressed by

,

where is Newton constant, that is, gravity is non-local but in a very subtle way.

Now, why exciting models are deeply flawed according to Nima? Well, Higgs phases of gravity violate “non-local” part in the statement above – they are manifestly local. On the other hand, DGP violates “subtle” part of the statement above, since it allows for superluminal propagation.

Basically, a general effective scalar field theory featuring CP violation looks like

.

DGP is a rather special CP violating theory, where the last term before the dots is canceled due to a special symmetry, and this allows theory to feature superluminal propagation.

He concluded by explaining what questions should one study to understand non-local nature of gravity better. Basically, since non-locality is suppressed by a factor , it should become important again in situations where some kind of enhancement is present – such as questions related to BH information paradox and eternal inflation (in the latter case, enhancement comes from the fact that you are never able to measure more than models in dS universe, where is de Sitter entropy).

I’ll try to cover remaining talks of the second day tomorrow.

Post from: NEQNET: The world of theoretical physics

Workshop on tests of gravity in Case Western – day 2 and Arkani-Hamed’s talk

The hot topic there nowadays is waterboarding – can it be really considered torture or not? And if this is torture, is it really acceptable to use torture against enemies of the State – for the sake of getting a piece of information regarding a forthcoming terroristic act, etc. etc.?

Well, Geneva conventions forbid torture even during war times, and US signed those conventions. Also, there are many examples in the history of US when people have been put to jail (or to death ) for torturing.

But surprisingly after a bit of thinking one finds that the ultimate truth is somewhat trickier than that and may even contain several levels of irony in it (you know how much I love irony).

And here is the first level. In US militiary, spec ops have a possibility to go through so called “torture training” (as far as I understand, the training is really optional). The idea is that a trainee is subjected to some kind of “simplified” torture procedures in order to increase his psychological stability under torture (just in case – what if the person gets captured during an operation and tortured?). The “torture training” procedures are planned and preformed in a way allowing to minimize any personal injuries of the “tortured” – that is, guys don’t have their nails teared out or the trainer hits the guy’s head against the rubber (not stone) wall (lol) etc. etc., you’ve got the idea.

This was exactly the program recommended after 9-11 to use against terrorists/enemies of the state who might have provided some valuable information concerning bin Laden & Co – since “something we use during our own soldiers’ training is certainly Ok to use against enemies of the State” (although there is of course a primary difference between the situation when a “tortured” person can make a sign calling to stop the procedure and when a “tortured” person does not have this possibility).

The second level of irony is that this very program was developed on the basis of certain Chinese manuals, used by North Korean and Vietnamese torturers back in 1950s-60s. As one understands, the main goal of that “Chinese torture program” wasn’t really getting some valuable information from the tortured. Instead, the goal was to break the tortured to use him later in propaganda wars – “broken” soldiers and officers were typically featured on certain tapes where they sweared allegance to communism and condemned capitalist-imperialist pigs. That’s why torture could not really mean any injury – a turned to the dark side should have looked and sounded presentably.

In this respect, I think, liberals correctly suppose that waterboarding and other interesting practices were really used to get additional points in the propaganda war, instead of getting information.

Via Boris Ivanov.

Post from: NEQNET: The world of theoretical physics

Two levels of irony of waterboarding

WATERLOO, Ontario, Canada, February 9, 2009 ? Dr. Neil Turok, Director of Canada’s Perimeter Institute for Theoretical Physics (PI), is pleased to announce the appointment of nine more outstanding international scientists to the positions of PI Distinguished Research Chairs.

The new Chairs include Yakir Aharonov of Chapman University, Nima Arkani-Hamed of the Institute for Advanced Study, Neta Bahcall of Princeton University, Juan Ignacio Cirac of the Max Planck Institute, Gia Dvali of CERN and NYU, Subir Sachdev of Harvard University, Ashoke Sen of the Harish-Chandra Research Institute, Leonard Susskind of Stanford University and Xiao-Gang Wen of MIT. They will join Perimeter Institute’s first Distinguished Research Chair, Prof. Stephen Hawking, in spending extended research visits at PI each year. The appointments are for three years. As PI grows, it plans to reach a steady state of 40 Distinguished Research Chairs.

In making the announcement, Dr. Turok stated, “We are delighted to welcome these eminent scientists to Distinguished Research Chairs at PI. Their research spans many of the most exciting areas in theoretical physics. Their presence will spark new scientific collaborations and provide invaluable guidance to us, as well as inspiring the budding young researchers on our new Perimeter Scholars International program. As past experience shows, when complementary insights are brought to bear and critical mass is reached, major advances are possible.”

In addition to building its team of resident scientists in Waterloo, Ontario, PI is becoming a second research home to many leading scientists from around the world. Each new Distinguished Research Chair will become part of PI’s research community while retaining their permanent positions at their home institutions. Below are details on each of the new Distinguished Research Chairs.

Yakir Aharonov is a professor of theoretical physics at Chapman University and Professor Emeritus at Tel Aviv University. He has made seminal contributions in quantum mechanics, relativistic quantum field theories and interpretations of quantum mechanics. In 1998, he received the prestigious Wolf Prize for his 1959 co-discovery of the Aharonov-Bohm effect. Prof. Aharonov is also a PSI Patron.

Nima Arkani-Hamed of the Institute for Advanced Study, is a leading particle physicist who has previously been a long-term visitor at PI, and is a member of the PSI faculty. Prof. Arkani-Hamed has developed theories on emergent extra dimensions, “little Higgs theories” and recently proposed new models that can be tested using the Large Hadron Collider (LHC) at CERN in Switzerland. You can view his past PI Public Lecture, “Fundamental Physics in 2010″, on the Perimeter Institute website.

Neta Bahcall is the Eugene Higgins Professor of Astrophysics at Princeton University. She is an observational cosmologist who has pioneered quantitative approaches to the understanding of astronomical data. These methods have enabled her to achieve key insights into such fundamental questions as the large-scale structure, mass, and fate of the universe, galaxy formation, the nature of quasars, and dark matter.

Juan Ignacio Cirac, Director of the Theory Division of the Max Planck Institute of Quantum Optics in Germany, is a leading quantum information theorist whose group recently received the 2009 Carl Zeiss Research Award. His research aims to characterize quantum phenomena, and to develop a new theory of information based on quantum mechanics, work which may ultimately contribute to the development of quantum computers.

Gia Dvali is the Silver Professor of Physics at New York University’s Center for Cosmology and Particle Physics and a member of the Theory Division at CERN, in Geneva. Prof. Dvali investigates fundamental questions at the intersection between particle physics and cosmology, including quantum gravity, and the very early universe. He has put forward ideas on large extra dimensions, large-distance modification of gravity and brane inflation in string theory, and suggested experimentally-testable explanations for the quantum stability of the weak interaction scale. Prof. Dvali’s PI research talk, “Cosmology and Gravity at Largest Observable Distances”, is available on PI’s website.

Subir Sachdev of Harvard University has made prolific contributions to quantum condensed matter physics, including research on quantum phase transitions and their application to correlated electron materials like high temperature superconductors. In recent years, Sachdev has exploited a remarkable connection between the electronic properties of materials near a quantum phase transition and the quantum theory of black holes. His 1999 book, Quantum Phase Transitions, has been described as “required reading for any budding theorist.”

Ashoke Sen, of the Harish-Chandra Research Institute in Allahabad, India, is a pioneering string theorist whose many contributions include the famous Sen Conjecture about open string tachyon condensation on unstable D-branes, as well as numerous insights about string dualities, and entropy in black holes.

Leonard Susskind is the Felix Bloch Professor of theoretical physics at Stanford University. Regarded as one of the fathers of string theory, Professor Susskind has also made seminal contributions to particle physics, black hole theory, and cosmology. His current research centers upon questions in theoretical particle physics, gravitational physics and quantum cosmology. Dr. Susskind has been an Associate Member of PI. He has also taken part in two PI Public Lectures, “The Black Hole Wars” and “The Physics of Information”.

Xiao-Gang Wen is the Cecil and Ida Green Professor of Physics in the department of Physics at MIT, and is also a member of the PSI faculty. He has proposed new topological phases of matter in condensed matter physics, and explored their applications, from fractional quantum Hall effects, to high temperature superconductivity, the emergence of photons and electrons, and the nature of space-time. These are elucidated in his recent book, Quantum Field Theory of Many-Body Systems.

ABOUT PERIMETER INSTITUTE

Canada’s Perimeter Institute for Theoretical Physics is an independent, non-profit, scientific research and educational outreach organization where international scientists cluster to push the limits of our understanding of physical laws and develop new ideas about the very essence of space, time, matter and information. The centre provides a multi-disciplinary environment to foster scientific collaboration in research areas of cosmology, particle physics, quantum foundations, quantum gravity, quantum information, superstring theory, and related disciplines. Located in Waterloo, Ontario, PI also provides a wide array of award winning outreach programs for students, teachers and the general public in order to share the joy of research, discovery and innovation. In partnership with the Governments of Ontario and Canada, Perimeter Institute continues to be a successful example of private and public collaboration in science research and education. A full history is available at www.perimeterinstitute.ca.

My warmest congratulations and cheers to PI postdocs, PI is becoming more and more exciting place to work in.

Post from: NEQNET: The world of theoretical physics

245. Interesting news from PI

The effect seems also to be related to the Problem N4 (confinement of quarks). I mentioned this idea several times on the blog, but do you really know how is it related?

Post from: NEQNET: The world of theoretical physics

227. Video of the day: Meissner effect in superconductors

Post from: NEQNET: The world of theoretical physics

201. Breaking Symmetry

D.: You said that chiral symmetry breaking is reduced to a Higgs mechanism in AdS/QCD. Chiral symmetry breaking does seem to be spontaneous symmetry breaking with pions? Goldstone bosons, but what would play the role of Higgs scalar in real QCD?

M.: This is slightly tricky: the bulk Higgs field is dual to the scalar operator , which indeed gets a VEV in QCD. But the scalar excitations in QCD are difficult to understand. In the 5D theory, there is a set of scalar modes arising as KK modes of the bulk Higgs. Unlike some of the other light mesons, there’s no straightforward way to match them to real states in QCD. Probably the thing that should be thought of as the lightest excitation of this operator is the , but in real QCD lots of other scalar operators are around and they mix a lot; scalar glueballs are likely to be heavier, and the lightest scalar pole (the sigma) is probably best thought of as a 4-quark state. But I am not an expert on this and people argue about it….

D.: Can you explain why one needs RR backgrounds with string scale curvature (you are talking about AdS curvature, right?) to get confimenent?

M. I am talking about AdS curvature, but it doesn’t have to be string scale to get confinement – only to get QCD-like confinement. The point is that in models with controlled duals, there is a hierarchy between the lightest (Kaluza-Klein-like) states and the stringier mesons. This hierarchy is absent in QCD; light states are already stringy. So we will need the full string theory if we are to someday understand them from a dual.

D.: The question about your paper ? would you say that there is a phase transition in , fixed that separates regimes of small and large ? Would you expect that QCD or gluodynamics in the large limit does not have a gravity dual?

M.: There is almost certainly no phase transition (I don’t know of any candidate for an order parameter). Since it’s hard to access the intermediate regime in any controlled calculation, I don’t really know what the transition looks like. In the paper we have a toy quantum mechanics model that shows what such a transition could look like if it is smooth. One interesting result of Klebanov, Maldacena, and Thorn (hep-th/0602255) is that in N=4 SYM, the spectrum of states of a static flux tube has an abrupt change at some critical . I don’t know if there can be similar changes in the spectrum of confining theories as you change the short-distance ‘t Hooft coupling. In any case, such a change is not a phase transition.

QCD and gluodynamics in the large limit should have a gravity dual in the sense that they are probably dual to some higher-dimensional string theory with a massless closed string graviton mode that corresponds to the stress-energy tensor of the boundary theory. On the other hand, Einstein gravity is not a good approximation to these theories, because the stringy states are light and play an important role in the dynamics.

D.: Thanks!

Post from: NEQNET: The world of theoretical physics

185. And more about AdS/QCD

Since I strongly doubted that Wallstreet financial analysts are so much ignorant (in this particular sense ) but was unable to prove at that time  why Sergey’s statement is wrong, I decided to go quickly through the literature. Of course, I immediately discovered that even in the end of 19th century no single financial analyst was paid an equivalent of present 100000 USD/year for attempts to approximate dynamics of stock prices by Gaussian distributions.

But before turning to my amazing discoveries , let me first explain why Gaussian distribution for the behavior of stocks  is actually not that bad What is actually meant by the Gaussian distribution?

Let be the price of a stock. We will call the quantity return (per unit time) of the stock. The claim is actually that return satisfies the following stochastic (Langevin) equation

, (1)

where the noise has correlation properties

, , (2)

of the Gaussian random field. The quantity determines  the volatility of the stock.

If the growth rate is contant, the solution of the equation (1) can be immediately found. It has the form

(3)

Quick exercise. Check it

Trivially, it descibes the exponentially growing price of the stock You might be surprised, but this is actually what is typically observed on markets in the long run. See for example this behavior of the Dow Jones Industrial for the last 30 years:

If one ignores an unpleasant 2000-2010 decade, DJIA behavior is nearly exponential. Also, the spectrum of the noise is typically nearly flat – especially, for markets with huge volume like FOREX. The basic recommendation that follows from the plot above (very well known to people who invest into mutual funds) – just follow the market. Invest in some index mutual fund and enjoy watching how your money grow together with the market. This strategy should work especially well for rich people like Worren Buffet, whose assets are bold enough to sustain strong fluctuations on the market – ultimately, markets grow exponentially.

But is it actually write? Take a look on the plot above now taking into account the 2000-2010 decade – it seems that exponentially growth was very effectively stopped (like it was in the middle 60s for example, when stagnation of DJIA continued for 20 years – till 1980). What is wrong with common lore about mutual funds we presented above and our naive formula (1).

Actually, many things we did not take into account are simultaneously important. first of all, volatility itself is a function of time, as well as the growth rate . Second, rare events have much higher probability than the one determined by the exponential tail of the Gaussian distribution, as was observed already in the end of the 19th century by Pareto.

But this is probably a subject for another post.

Post from: NEQNET: The world of theoretical physics

160. Quantitative analysis for beginners. Dumb Gaussian approximation

Merry Christmas again to you, readers of NEQNET!

Post from: NEQNET: The world of theoretical physics

151. No blogging for Xmas!

As many of you have noticed, Google have recently won the major lawsuit against publishers and authors. Here is the first consequence.

Google has just announced that it is going to include all issues of such magazines as

• Popular Science
• Popular Mechanics
• Man’s Health
• Bulletin of the Atomic Scientists
• Maximum PC
• many others

into the Google Books index. Enjoy!

Post from: NEQNET: The world of theoretical physics

136. Google Books now include magazines

I just recieved the following email:

Professor Stephen Hawking to Regularly Visit Canada’s Perimeter Institute as Distinguished Research Chair

Waterloo, Ontario, Canada, November 27, 2008 – Dr. Neil Turok, Director of Canada’s Perimeter Institute for Theoretical Physics (PI), is pleased to announce the appointment of internationally renowned scientist Professor Stephen Hawking to the position of PI Distinguished Research Chair.

Prof. Hawking will conduct regular stays at PI in coming years, beginning in the summer of ’09, and says, “I am honoured to accept the first Distinguished Research Chair at the Perimeter Institute. The Institute’s twin focus, on quantum theory and gravity, is very close to my heart and central to explaining the origin of the Universe. I look forward to building a growing partnership between PI and our Centre for Theoretical Cosmology, at Cambridge. Our research endeavour is global, and by combining forces I believe we will reap rich rewards.”

In announcing that Prof. Hawking will visit PI for extended periods each year, PI Director Neil Turok said, “The appointment marks a new phase in our recruitment that will see leading scientists from around the world establish a second ‘research home’ at Perimeter Institute. I am delighted that Stephen has agreed to accept the first of a projected 40 such visiting Chairs. We look forward to hosting Stephen in Waterloo, Ontario, to benefiting from his wise mentorship and guidance which has been so successful in Cambridge, and to the many stimulating scientific collaborations which will undoubtedly emerge.”

Via Bee.

First Lenny Susskind, then Hawking… PI becomes really great place to work at. And what is left for us, Europeans? It looks like soon the only way for us to taste Hawking’s wisdom will be to read his “Large scale structure of spacetime” or to watch his Youtube lectures:

Post from: NEQNET: The world of theoretical physics

116. Hawking at PI

Apart from improving the way of life, what is actually done during all these years? What am I proud of? I have GREAT wife (I am really lucky in this respect, so much luckier that people around). To get married so sucessfully is definitely an achievement. I have spent some time to get some really good education (not in humanities though or languages – it would be so good to know a couple of European languages well). I work on things I, myself, want to work on. What else? I am not quite sure.

Post from: NEQNET: The world of theoretical physics

56. Birthday

According to AdS/CFT duality, supergravity on describes physics of SYM at large ‘t Hooft coupling . This is not quite what we need though because:

a) SYM is conformal field theory, while QCD is asymptotically free (coupling becomes stronger in the IR).

b) that QCD we are interested in from the practical point of view actually corresponds to .

On the other hand, we can try to take AdS/CFT as zero approximation for description of strong coupling QCD, since the latter is approximately conformal at large energies (I have an impression that the word “approximately” here is more about what one has to believe in rather than something one can consistently check, but I may be wrong). So, we start with geometry describing 4d physics of YM CFT at high energies and then somehow introduce a cutoff in 5th dimension in order to induce confinement for the 4d Yang-Mills theory. This cutoff can be either introduced by hands (this is what is called “hard wall AdS/QCD limit”) or dynamically (such as by introducing non-trivial dilaton background – situation of “soft wall AdS/QCD” under present discussion).

As it turns out, in order to reproduce linear Regge trajectories, one has to introduce a dilaton background which is quadratic w.r.t. conformal coordinate of AdS:

(1).

The question however is whether it is possible to continue the reverse engeneering process a step further compared to Stephanov et al. and find a selfconsistent solution of supergravity equations such that the gravitational background is and the dilaton background is given by (1).

Tony has introduced a model naturally predicting such a background. The price to pay is that he had to introduce an additional scalar field (he wants to identify it with closed string tachyon of non-critical string theory – note that here happens a trick: we don’t want to find consistent 10 dim background of the form, but limit the discussion to 5 dim instead) and a very nontrivial potential for the dilaton and the field . The effective action for the 5-dim theory is (I am not sure I have to present it here, but I will)

where

.

Looks scary, doesn’t it?

Since the potential is reverse-ingeneered, it was impossible for me to understand the physical meaning of the potential form (or how it would follow from a stringy model).

Let me finish with a couple of notes:

1) It would be interesting to understand how this model works for the 2D QCD which is exactly solvable – it would correspond to gravity in , which is presumably topological (it is a theory of scattering of conical defects produced by the quanta of and ).

2) It will be hard to explain the nature of the field and the corresponding terms in the potential from the stringy point of view (we should stick to 10 dim physics in this case). As Tony shows, also has to have a runaway behavior (linear growth with ). I wonder – can be one of the moduli which don’t get stabilized?

Post from: NEQNET: The world of theoretical physics

51. Planck 2008: day 4 – Soft wall AdS/QCD

Plenary talks of the 4th day were mostly devoted to unparticles and AdS/QCD, with opening talk by Howard Georgi, inventor of unparticles himself. He was talking about his paper (just released) “An unparticle example in 2D” with Eugene Kats (projector did not work in the beginning of his talk, so he had to talk without transparances or PowerPoint presentation, and I was very much impressed how well he did it).

Let me first remind you what is the buzz concering unpartcles. Imagine some scale invariant matter (that is, spectrum of its excitations is scale invariant). One cannot describe such fields (let us call them ) in terms of particles – the possibility of the latter description would imply that the spectral function of excitations (exp. value of the commutator ) has strong peaks at some . Positions of the peak would be related to the mass of the “particles”, while widths of the peaks – to the life time of the “particles”. Scale invariant spectral function therefore means that our particles are interacting so strongly, that their notion is undefined.

This scale invariant matter sector can in principle weakly interact with our Standard Model stuff, and its existence can potentially influence SM scattering, in particular, would lead to events of missing energy and momentum in scattering events. Since unparticles are described by CFT, interactions between them and SM are organized as interactions between SM fields and CFT operators with non-trivial scaling dimensions (Georgi calls them Banks-Zaks fields).

After this short introduction, let me go back to Georgi’s talk… He explicitly introduced an example of the 2D theory with unparticles: Thirring model (massless fermions, 4-fermion interaction; the model is exactly solvable, admits bosonization and is nothing else but CFT) with massive vector bosons. The Thirring model with massive gauge bosons turns also out to be exactly solvable. At higher energies the theory approaches free field limit, while in the IR massive vector bosons are integrated out, only fermions survive, so conformal symmetry gets restored (one has Thirring model unparticles).

As a “SM” stuff, Georgi introduces complex scalar field interacting with Thirring fermions through standard trilinear interaction term, so that we can excite unparticles in collisions .

The physics of scattering turns out to be the following: first of all, there exists the physical scale

where is the mass of gauge bosons and is their interaction with Thirring fermions. At one has energy loss to unparticles, while at one can also excite gauge bosons. enters the overall cross section pretty much in the same way enters cross sections in inclusive QCD processes.

The second talk about unparticles was by John Terning (UC Davis): he discussed AdS/CFT-unparticle interplay. He basically showed that unparticle actions are equivalent to holographic boundary actions for fields in AdS. Clearly, his picture cannot be universal since the class of CFTs is much wider than the class of theories that admit gravity dual.

The talk N3: Antonio Delgado (Notre Dame) has introduced an interaction between Higgs and unarticle stuff of the form

where is the CFT operator with dimension and tried to figure out how it will influence Higgs physics at LHC. The result of the Higgs-unparticle interplay is the
mass gap in the unparticle continuum and a shift in the Higgs mass. In fact, Higgs state can be above (bound state in unparticle continuous spectrum) or below the mass gap. Also, another isolated state, a mix of Higgs and unparticles (Antonio calls it phantom Higgs), can appear in the spectrum near or below the mass gap. Coupling between phantom Higgs, fermions and gauge bosons are reduced.

During the next talk (“A bound on operator dimension in CFT4 and the hierarchy problem” by Riccardo Ratazzi) I decoupled from the audience and missed it almost completely, but the final talk by Tony Gherghetta has grabbed my attention back. Tony was talking about soft-wall AdS/QCD, the subject that definitely deserves a separate post.

To be continued…

Post from: NEQNET: The world of theoretical physics

50. Planck 2008: day 4