Small Window to Particle Physics

Zeitgeist String Era

2006-10-06T14:38:00.000+03:00

Bert Schroer has written a very interesting essay (the kind I've been hoping to write some day ;) String theory and the crisis in particle physics. A historical overview of quantum theory is also given, back from the 1920's. Making use of the clarity of style of the author I give a few quotes of his text as a warm-up for a potential reader. Mainly from the introduction, to avoid mentioning any names of people involved ;).

"For the present particle theorist to be successful it is not sufficient to propose an interesting idea via written publication and oral presentation, but he also should try to build or find a community around this idea. The best protection of a theoretical proposal against profound criticism and thus securing its longtime survival is to be able to create a community around it. If such a situation can be maintained over a sufficiently long time it develops a life of its own because no member of the community wants to find himself in a situation where he has spend the most productive years on a failed project. In such a situation intellectual honesty gives way to an ever increasing unwillingness and finally a loss of critical abilities as a result of self-delusion."

"I would like to argue that these developments have been looming in string theory for a long time and the recent anthropic manifesto [1] (L. Susskind, The Cosmic Landscape: String Theory and the Illusion of Intelligent Design) (which apparently led to a schism within the string community) is only the extreme tip of an iceberg. Since there has been ample criticism of this anthropic viewpoint (even within the string theory community), my critical essay will be directed to the metaphoric aspect by which string theory has deepened the post standard model crisis of particle physics. Since in my view the continuation of the present path could jeopardize the future research of fundamental physics for many generations, the style of presentation will occasionally be somewhat polemic."

"An age old problem of QFT which resisted all attempts to solve it is the problem of existence of models i.e. whether there really exist a QFT behind the Lagrangian name and perturbative expressions. Since there are convincing arguments that perturbative series do not converge (they are at best asymptotic expressions) this is a very serious and (for realistic models) unsolved problems. The problem that particle physics most successful theory of QED is also its mathematically most fragile has not gone away. In this sense QFT has a very precarious status very different from any other area of physics in particular from QM. This is very annoying and in order to not to undermine the confidence of newcomers in QFT the prescribed terminology is to simply use the word ”defined” or ”exists” in case some consistency arguments (usually related in some way to perturbation theory) have been checked."

"These problems become even worse in theories as string theory (which in the eyes of string protagonists are supposed to supersede QFT). In this case one faces in addition to the existence problem the conceptual difficulty of not having been able to extract characterizing principles from ad hoc recipes. Unlike in renormalizable QFT there exists up to date no n-th order proof that string theory is free of renormalization parameters."

"Since there was no operator formalism in which the underlying ideas (invariance, unitarity, crossing, maximal analyticity) could have been implemented, the problem of constructing a crossing symmetric, unitary, maximally analytic S-matrix was ill-formulated. Tinkering with properties of Beta functions and their representation in terms of Gamma functions, Veneziano was able to construct the first model for an apparent crossing symmetric elastic scattering amplitude. His proposal did not satisfy unitarity, but the realization that his on-shell prescription allowed an auxiliary field theoretic description in terms of a (off-shell) two-dimensional conformal field operators theory and that it also admitted an auxiliary presentation in terms of the canonical quantization of a classical relativistic Nambu-Goto string Lagrangian contributed significantly to its theoretical attraction. It also nourished the hope that the model can be unitarized in a later stage. Its main popularity it however enjoyed among strong interaction phenomenologists who actually (for reasons which nowadays hardly anybody remembers) liked the idea of satisfying crossing already with infinite towers of intermediate particle states, duality = crossing among with (infinitly many) one-particle without the participations without the participation of the multi-particle scattering continua as would be required for an S-matrix coming from QFT. In conjunction with the phenomenological use of ideas of Regge poles, the emerging trajectory pictures (mass versus spin) had a certain phenomenological charm, and although infinite particle towers cause some field theoretic headache, there was no reason to reject it as a phenomenological proposal which captures some aspects of strong interactions and to worry about those conceptual problems later."

"But this never happened; the dual model became a phenomenological orphan and after its string-theoretic completion, by the time it was presented as a TOE (this time including gravity), the conceptual problem behind the crossing-duality relation was forgotten, and a chance to understand something about conceptual relations of string theory to QFT was (presumably permanently) lost. Particle physics these days is generally not done by individuals but by members of big groups, and when these big caravans have passed by a problem, it will remain in the desert. A reinvestigation (naturally with improved mathematical tool and grater conceptual insight) could be detrimental to the career of somebody who does not enjoy the security of a community."

"In its new string theoretical setting its old phenomenological flaw of containing a spin=2 particle was converted into the ”virtue” of the presence of a graviton. The new message was the suggestion that string theory (as a result of the presence of spin two and the apparent absence of perturbative ultraviolet divergencies) should be given the status of a fundamental theory at an energy scale of the gravitational Planck mass ∼ 10^19 GeV i.e. as a true theory of everything (TOE), including gravity. Keeping in mind that the frontiers of fundamental theoretical physics (and in particular of particle physics) are by their very nature a quite speculative subject, one should not be surprised about the highly speculative radical aspects of this proposals; we know from history that some of our most successful theories originated as speculative conjectures. What is however worrisome about this episode is rather its uncritical reception. After all there is no precedent in the history of physics of a phenomenologically conceived idea for laboratory energies to became miraculously transmuted into a theory of everything by just sliding the energy scale upward through 15 orders of magnitudes and changing the terminology without a change in its mathematical-conceptual setting."

Finally, from Conclusions:
"In this essay I emphasized that, as recent progress already forshadows, the issue of QG will not be decided in an Armargeddon between ST and LQG, but QFT will enter as a forceful player once it has conceptually solidified the ground from where exploratory jumps into the blue yonder including a return ticket can be undertaken."

"The problem is not that there are no other games in town, but rather that there are no bright young players who take the risk of jeopardizing their career by learning and expanding the sophisticated rules for playing other games."

By the way, I wrote my (modest) thesis on five point Veneziano phenomenology.
Now, probably back to break (due to ailing health).

Having Break

2006-09-23T14:26:00.000+03:00

This blog continues to be inactive for some time.

Preons: Generation Number from Space Dimension

2006-05-17T14:26:00.000+03:00

The preon model, ie. that quarks and leptons and some other particles would be composites of more elementary constituents, has been under consideration for some thirty years. These days only really few people seem to give any attention to preons. On the other hand, the motivation of the preons has been in grand unification schemes, and even in heterotic superstring theories.

Any preon model would need some novel features with respect to QCD: like understanding why the masses of quarks and leptons are very much smaller than their inverse sizes. O.W. Greenberg proposes in a recent paper A Schematic Model of Generations a possible solution to this and other problems of preon models. He introduces for the preon interaction the group [SU(3) x SU(3)]_b. The preons of his model are

6x6 of [SU(3)xSU(3)]_b hexon: spin ½ color, lepton, flavor, helicity,
3x3 generon: spin 0, [SU(3)xSU(3)]_b degrees of freedom, and
[SU(3)xSU(3)]_b bindon: gauge boson

The author requires the generations to be gauge group single-centered singlets. He finds three composites that meet the requirements hg^-g^- , hggg^- , and hgggg. For the first generation the antigeneron repulsion leads to linear quasi-one dimensional configuration, and for the second generation the (anti)generon repulsion to triangular quasi-two dimensional configuration, and for the third generation to tetrahedral quasi-three dimensional configuration. As simple as that!

The author associates the dimensionless factor L/a, where L is the large linear scale of the generations and a is small linear scale, with the mass ratios between the generations, so that the mass scales of the successive generations are proportional to La², L²a, and L³, respectively. He finds L/a to be about 100.

Generation mixing, dark matter (gg^-) and some generic predictions of preon models, like higher spin particles, are also considered. But the author postpones the discussion of the weak bosons and the Higgs mesons or their substitutes to a later paper. As well as a few other questions.

Towards the ILC?

2006-05-03T14:58:00.000+03:00

I have been quite confused, suppose like many others, of the developments in string theory getting acceptance by prominent physicists for the
landscape ideology. Therefore it felt good to read the news about one of the best known string "Wunderkinds" Brian Greene going to address the Congressional Research and Development Caucus Advisory Committee in DC on May 9, 2006. His talk is titled "Reaching for Einstein's Dream: The Quest for the Deepest Laws of the Universe."

The Director of DOE's Office of Science, Raymond L. Orbach, will present the new High Energy Physics Advisory Panel publication "Discovering the Quantum Universe," a companion volume to the "Quantum Universe." The new document explains the outstanding discovery opportunities at the Large Hadron Collider and the proposed International Linear Collider. Both publications will be available at the meeting and can be downloaded at http://interactions.org/quantumuniverse/. As Lubos Motl has recently shown the need for the ILC is well indicated ;-)

Though the LHC is beginning operations next year, I understand the above activities as necessary preparations to go experimentally beyond the Standard Model.

(Sent by mobile mail)

Inventors in the Landscape

2006-04-20T20:32:00.000+03:00

Bert Schellekens has written a note The Landscape "avant la lettre" on the history of string theory landscape as he has experienced it. Whatever one's opinion of string theory and the landscape in particular, nightmare or brightware, it is pretty safe to say that most of us have had such periods as Schellekens, at some time, perhaps with less grandiose problems. In the golden 1960's, George Zweig must have been very frustrated.

After some leisurely thinking, I accept, for the moment, the landscape may be a logical possibility after all. It would imply a radically new (less attractive, fuzzy) paradigm for fundamental physics. It may even have some support from the arguments of no boundary initial condition theory, as discussed by S. Hawking and T. Hertog. Look also here and here.

I quote parts of Schellekens' paper, first from the introduction:

    "In 2003 L. Susskind published his paper entitled “The Anthropic Landscape of String Theory” [1], which I read with great pleasure. The reason was that, many years before, I had come to the conclusion that everything we knew about String Theory was pointing towards an “anthropic landscape” of vacua. I had advocated this idea consistently during many years, on the basis of far less evidence than we have today. It seemed obvious to me, but the response I got was frustrating."

    "I have considered many times writing a paper about my ideas, but I could not bring myself to write something that seemed so obvious. It would have been a paper with many words an no formulas, and it was not at all clear where to publish it. There were no blogs, no homepages, no “arxives”, and no obvious journal to send it to. And furthermore the hard evidence was not available yet. One valid objection was that we did not know enough about string theory yet to make any claim about the existence of a large number of non-supersymmetric, stable vacua. Today that is still an often-heard objection. My feeling about that was exactly what was written in [1], “if we ﬁnd one such vacuum we are going to ﬁnd a huge number of them”. To me that was clearly the message String Theory was sending us already in 1986, but most people preferred to ignore it, although of course everyone agreed that the number of supersymmetric vacua was huge."

    "It is difficult and dangerous to claim with the beneﬁt of hindsight that one arrived at some conclusion at a particular time. After 1986 it took some time to understand that all four-dimensional string vacua that were proliferating quickly had moduli, and that this was an important problem. It took some time to appreciate that they were all related to each other, and could be thought of as ground states of one theory, the Heterotic string. And of course there were ﬁve string theories, not just one. The most common attitude was to ignore the others and assume that one day we might know what was wrong with them. This was also my point of view until 1994, but uniqueness of the underlying theory was anyhow not the most crucial part of the argument. Apart from that issue, I was already defending a point of view quite similar to the one expressed in the 1998 speech during my time at CERN, which in any case means before 1992. I had discussions about that with many people and encountered a lot of resistance, and I do not recall anyone wholeheartedly agreeing with me. It is therefore somewhat strange that after 2003 some people started telling me “this is what I have always been saying”."

    "Most people associate the Landscape with an anthropic solution to the cosmological constant problem. For me that was not the crucial issue. Even if we came to the conclusion that the cosmological constant was not anthropically tuned after all, I would still expect an anthropic landscape for the structure and parameters of the standard model. String Theory was the ﬁrst and so far only theory that made the question about uniqueness of the standard model unavoidable. Most, if not all, other attempts to “derive” the structure of the Standard Model involve a new layer of gauge theories, for example composite models or GUTs. Then on inevitably runs once again into the same problem one tries to solve, namely an essential non-uniqueness. The most promising candidate, SO(10) Grand Uniﬁcation, requires an unexplained triplication of families and has a large number of parameters, even if one takes this choice of gauge group for granted. The only hope for uniqueness is a theory that itself has a chance of being unique, namely a theory of gravity. Such a theory, String Theory, was explored during the past decades, and it gives a very clear answer: there is no unique ground state, but a landscape of vacua. It is in my opinion the only answer that makes sense, and the fact that this answer came out of String Theory is a sign that we are on the right track. I see this as a fundamental result that may even survive if String Theory turns out to be incorrect, or if String Theory is just the tip of an iceberg."

    "I expect that the String Theory Landscape will acquire an important place in science history. Of course its ultimate fate depends on the correctness of String Theory, and the unexpectedly huge size of the landscape is making it a lot harder to convince ourselves of that. But String Theory won’t be correct without the landscape being correct. And if that is true, it would be one the most fundamental discoveries one can make. It implies that we would know the answer to Einstein’s question if the creator of our Universe had any choice: indeed, we would know all the choices. This insight is probably the most important one we have obtained from string theory so far. It should be remembered that in 1984 this would have been completely unthinkable. Unlike the other main result we hope to get out of String Theory, consistent Quantum Gravity, the landscape emerged against everyone’s initial expectations and wishes. It is a revolution that is unfolding so slowly that few people even recognize it as such. But nevertheless, discovering that our standard model is just one entity in a huge landscape, and hence cannot be completely derived from ﬁrst principles, is a paradigm shift for our ﬁeld."

From the original talk, translated into English:

    "This line of thought ﬁts in very well with a series of insights that pointed out our modest place in the cosmos. Our planet is not the center of the solar system, our sun is just one of many stars and not even a very special one, and the same is true for our galaxy. It seems natural to assume that also our universe, including the quarks, leptons and interactions we observe is just one of many possibilities."

    "This way of thinking has important consequences. If indeed our universe, including its laws of physics and the entire Standard Model is just one of many possibilities, this implies that there are limits to what we can compute. The properties of the quarks and leptons, their interactions and the parameters of the Standard Model (or at least part of them) were ﬁxed at the birth of our universe, when a choice was made out of the many possibilities. We will never be able to compute that choice, because it could just as well have been diﬀerent."

    "I have the impression that many of my colleagues believe or hope that this will ultimately not be the case. They hope to ﬁnd a kind of mathematical formula that has only one solution. That single solution should then correspond to our four-dimensional world, including all quarks, leptons and the four basic forces. Also the values of the nineteen (or more) parameters, such as the masses of all particles, should then ultimately emerge as the outcome of a mathematical computation."

The final paragraph:

    "The foregoing was a sketch of a possible end of the story. It is the end that given the current state of aﬀairs seems the most desirable to me, but in the end only hard results matter. Nature will probably not care much about my wishes. Despite the word “end” in the title it was not at all my intention to suggest that the end will be reached soon. On the contrary, it will take many decades of work to produce a complete map of String Theory. I am looking forward to an exciting continuation of this adventure."

[1] L. Susskind, “The anthropic landscape of string theory” arXiv:hep-th/0302219.

Finally, remember that some string and other theorists retire sooner, some later ;-)

Cosmological Constant and the String Landscape at Solvay 2005

2006-04-04T12:12:00.000+03:00

This is a rapporteur's talk at the 23rd Solvay Conference by Joe Polchinski, the article is dated March 31, 2006. (I feel it is the best paper of the year until now.) The author divides theories of the cosmological constant (CC) into two groups: value fixed by theory and value adjustable like in string theory landscape. The central issue in the report is to discuss the extent to which physics is predictable. Polchinski sees three major questions in the CC: why it is not large, not zero, but comparable to the matter density now. He focuses mainly in the first question: "this is hard enough!"

The fixed value theories are discussed comparing the problem to Lamb shift (main topic in the 1947 Shelter Island conference). The author leads the reader through the Lamb shift in the presence of external gravitons discussion to short and long distance modifications to gravity. There is no solution visible in those directions.

In the adjustable scenario, several possibilities are mentioned: unimodular gravity, non-propagating four-form field strengths, scalar potentials with many minima, rolling scalar with nearly flat potential, spacetime wormholes, self-tuning, and explicit tuning (one or more free parameters). Among the mechanisms leading to the observed CC value the following are discussed: the Hartle-Hawking wavefunction favoring the smallest positive value of CC, the de Sitter entropy suggesting that the HH wavefunction has some statistical interpretation in terms of the system exploring all possible states, and the Coleman-de Lucchia amplitude for tunneling from positive to negative CC vanishing for some parameter range keeping the universe in the state of smallest positive energy density. Polchinski considers all these tantalizing in the same way as supersymmetry is as a solution for the CC problem. These mechanism would work in an empty universe. Next, I quote "In the course of trying to find selection mechanisms, one is struck by the fact that, while it is difficult to select for a single vacuum of small cosmological constant, it is extremely easy to identify mechanisms that will populate all possible vacua — either sequentially in time, as branches of the wavefunction of the universe, or as different patches in an enormous spatial volume. Indeed, this last mechanism is difficult to evade, if the many vacua are metastable: inflation and tunneling, two robust physical processes, will inevitably populate them all.

But this is all that is needed! Any observer in such a theory will see a cosmological constant that is unnaturally small; that is, it must be much smaller than the matter and energy densities over an extended period of the history of the universe. The existence of any complex structures requires that there be many ‘cycles’ and many ‘bits’: the lifetime of the universe must be large in units of the fundamental time scale, and there must be many degrees of freedom in interaction. A large negative cosmological constant forces the universe to collapse to too soon; a large positive cosmological constant causes all matter to disperse. This is of course the argument made precise by Weinberg, here in a rather minimal and prior-free form.

Thus we meet the anthropic principle. Of course, the anthropic principle is in some sense a tautology: we must live where we can live. There is no avoiding the fact that anthropic selection must operate. The real question is, is there any scientific reason to expect that some additional selection mechanism is operating?

If there is a selection mechanism, it must be rather special. It must evade the general difficulties outlined above, and it must select a value that is almost exactly the same as that selected by the anthropic principle, differing by one order of magnitude out of 120. Occam’s razor would suggest that two such mechanisms be replaced by one — the unavoidable, tautological, one. Thus, we should seriously consider the possibility that there is no other selection mechanism significantly constraining the cosmological constant. Equally, we should not stop searching for such a further principle, but I think one must admit that the strongest reason for expecting to find it is not a scientific argument but a psychological one: we wish fundamental theory to be as predictive as we have long assumed it would be."

That's correct, next comes a discussion of the string landscape. And a chapter "What is String Theory?" This is very interesting, of course. But the best I can do is to recommend everybody to read Polchinski's talk! Final quote from the end: "Let me close with a quotation from Dirac: One must be prepared to follow up the consequences of theory, and feel that one just has to accept the consequences no matter where they lead. And a paraphrase: One should take seriously all solutions of one’s equations. Of course, his issue was a factor of two, and ours is a factor of 10^500."

Surface Paradigm for Dark Energy

2006-03-09T16:39:00.000+02:00

There has been indications that the dark energy and dark matter have their origin in general relativity, with some extensions. T.Padmanabhan discusses dark energy as the Mystery of the Millennium (an optimist would hope a decade or two). Dark matter discussion is given in the references of this paper.

The author assumes the dynamics of gravity follows from an approach which uses only the surface term of the Hilbert action for the continuum. Gravity has thermodynamic origin in this approach. The surface term's variation is related to entropy TdS and the matter term's variation gives PdV and dE terms. The entire variation is equivalent to the known equality between these. The main point I quote and condense:

Within the true theory of quantum gravity, measurable quantities should be the fluctuations in the vacuum energy and not the absolute value of the vacuum energy. The cosmological constant is most likely a low energy relic of quantum gravitational effects, arising from the surface term alone. This procedure is applicable to a large class of theories, including Gauss-Bonnet type actions in higher dimensions (superstrings). This suggests that the mechanism for ignoring the bulk cosmological constant is likely to survive quantum gravitational corrections which are likely to bring in additional, higher derivative, terms to the action. In a universe with two length scales L_Lambda (proportional to the Hubble radius) and L_p, the vacuum fluctuations will contribute an energy density of the correct order of magnitude r_DE =√rho_IR rho_UV, according to the author.
Addendum (more refs.)

General Relativity and Galactic Distances

2006-03-02T14:12:00.000+02:00

My colleague T. Perko informed me of a paper by H. Balasin and D. Grumiller titled Significant reduction of galactic dark matter by general relativity. The authors model the matter content of a galaxy by a pressureless perfect fluid. Stationarity and axial symmetry are also imposed on the solutions of Einstein equations. Using some simplifications they solve the linear partial differential equations and conclude that the Newtonian approximation over-estimates the amount of matter in a galaxy by about a third. GR reduces the amount of dark matter needed to explain the flat rotation curves.

An earlier paper by F. I. Cooperstock and S. Tieu, titled General Relativity Resolves Galactic Rotation Without Exotic Dark Matter, makes a stronger claim of the dark matter needed in galaxies. Using a similar perfect fluid model they end up to one linear and one non-linear equation relating the angular velocity to the fluid density. From their calculation the authors conclude that the need for a massive halo of exotic dark matter is removed.

We most likely will see other studies of general relativistic galactic systems, and new estimates of the amount of dark matter in the universe. For the present, we tend consider the latter paper's conclusion somewhat striking.

Entanglement at High Temperature

2006-02-24T12:05:00.000+02:00

Aires Ferreira, Ariel Guerreiro, and Vlatko Vedral have published interesting results on entanglement in Phys. Rev. Lett. 96 060407. I quote the authors:

" ... the entanglement between macroscopic mirror and a cavity mode field can arise due to radiation pressure at arbitrarily high temperatures as the system evolves in time. This is very surprising because it is commonly believed that high temperature completely destroys entanglement. We will study entanglement in the time domain using a discrete variable method and identify its dependence on the relevant physical parameters, such as the strength of the radiation pressure coupling and temperature."

Quarks, Strings, Branes, and Gravity

2006-02-23T20:20:00.000+02:00

Nick Evans, Southampton Univ., has written an article in Nature 439, 921-923 (23 February 2006) titled Quarks on a gravitational string. Short and readable for non-specialists, one figure, gives references to technical papers.

Gary Horowitz and Joseph Polchinski have written a contribution to "Towards Quantum Gravity" titled Gauge/Gravity Duality. Excellent coverage of this central topic. References given to the classical papers.

Joshua Erlich, Graham D. Kribs, and Ian Low wrote a paper Emerging Holography. The authors rederive the AdS/CFT predictions by a four dimensional approach.

Refining MOND: This is NOT Newton's Apple

2006-02-13T19:38:00.000+02:00

H.S. Zhao and B. Famaey have published their arXiv paper Refining MOND interpolating function and TeVeS Lagrangian in The Astrophysical Journal, 638:L9–L12, 2006 February 10. A soft introduction to this paper can be read at Interactions.org.

Hawking and no boundary initial conditions in the landscape

2006-02-10T08:45:00.000+02:00

As if the authors knew of each other, the previous post was about Hartle, and today it is Hawking together with Hertog! The title is Populating the Landscape: A Top Down Approach. The paper is very clearly written. The top-down approach is compared to bottom-up way. Predictivity of the approach is discussed. Being not able to write anything of it better, I give a few quotes:

From their abstract: "We put forward a framework for cosmology that combines the string landscape with no boundary initial conditions. In this framework, amplitudes for alternative histories for the universe are calculated with final boundary conditions only. This leads to a top down approach to cosmology, in which the histories of the universe depend on the precise question asked."

Later " ... the quantum state of the universe at late times is likely to be independent of the state on the initial surface. This is because there are geometries in which the initial surface is in one universe and the final surface in a separate disconnected universe. Such metrics exist in the Euclidean regime, and correspond to the quantum annihilation of one universe and the quantum creation of another. Moreover, because there are so many different possible universes, these geometries dominate the path integral. Therefore even if the path integral had an initial boundary in the infinite past, the state on a surface S at late times would be independent of the state on the initial surface. It would be given by a path integral over all metric and matter field configurations whose only boundary is the final surface S. But this is precisely the no boundary quantum state."

"In the bottom-up picture it is thought that the universe begins with a grand unified symmetry, such as E8 ×E8. As the universe expands and cools the symmetry breaks to the Standard Model, perhaps through intermediate stages. The idea is that string theory predicts the pattern of breaking, and the masses, couplings and mixing angles of the Standard Model. However, as with the dimension of space, there seems to be no particular reason why the universe should evolve precisely to the internal space that gives the Standard Model. It is therefore more useful to compute no boundary amplitudes for a spacelike surface S with a given internal space. This is the top down approach, where one sums only over the subclass of histories which end up on S with the internal space for the Standard Model."

From conclusions: "A central idea that underlies the top down approach is the interplay between the fundamental laws of nature and the operation of chance in a quantum universe. In top down cosmology, the structure and complexity of alternative universes in the landscape is predictable from first principles to some extent, but also determined by the outcome of quantum accidents over the course of their histories."

Hartle on Quantum Spacetime

2006-02-07T21:13:00.000+02:00

James B. Hartle has written a contribution to the 23rd Solvay Conference titled Generalizing Quantum Mechanics for Quantum Spacetime. It was delivered there by Murray Gell-Mann and David Gross in the absence of the author (I wonder how many people would have such eminent proxies ;-). The paper is very pedagogically written, starting practically from textbook QM which Hartle developes into a more general form.

"The key idea is that the fine-grained histories do not have to represent evolution in spacetime. Rather they can be histories of spacetime." In a sentence, branch state vectors can be constructed for each coarse-grained history by summing over the metrics and fields in the corresponding class of fine-grained histories. Considerations in signature lead to the conclusion "... if we live in a large universe it must have one time and three space dimensions." Now, if you are not very familiar with Hartle's work it is up to you to read the rest. -- At least try to avoid the two famous bloggers on the right concentrating at the moment in cartoons and movies ... ;-)

Dark Matter Temperature Measurement

2006-02-06T21:29:00.000+02:00

BBC News science reporter Jonathan Amos interviews (February 5, 2006, 23:25 GMT) Gerry Gilmore, IoA, Cambridge, on first measurements of properties of dark matter:

"It looks like you cannot ever pack it smaller than about 300 parsecs - 1,000 light-years; this stuff will not let you. That tells you a speed actually - about 9km/s - at which the dark matter particles are moving because they are moving too fast to be compressed into a smaller scale."

"The speed is a big surprise. Current theory had predicted dark matter particles would be extremely cold, moving at a few millimetres per second; but these observations prove the particles must actually be quite warm (in cosmic terms) at 10,000 degrees."

Emergent Spacetime

2006-02-01T21:04:00.000+02:00

Nathan Seiberg's review Emergent Spacetime (hep-th 0601234) is most interesting, at least to non-stringy people (with some exceptions, of course). Being at the moment out of town (AdS) near the boundary of the Baltic Sea, and having limited knowledge in these questions I just give some quotes from the conclusions. Seiberg gives no equations, apart from short definitions within the text, so the review is in principle layman readable ;-).

"One challenge is to have emergent spacetime, while preserving some locality - at least macroscopic locality, causality, analyticity, etc. Particularly challenging are the obstacles to formulating physics without time. It is clear that in order to resolve them many of our standard ideas about physics will have to be revolutionized."

"Understanding how time emerges will also have other implications. It will address deep issues like the cosmological singularity and the origin of the Universe."

"With so many different definitions we are tempted to conclude that we should not ask the question: "What is string theory?" Instead, we should ask: "Which string theories have macroscopic dimensions?" Although we do not have an answer to this question, it seems that large N will play an important role in the answer." (Sent as text by wireless webmail.)

Dark Sector of the Universe the Henan Way

2006-01-26T12:19:00.000+02:00

The dark sector, energy and matter, of the universe is under intensive study these days for good reasons. A proposal for the dark stuff comes from Henan, China (some 400 km to the east of Shanghai). Mian Wang sets up an alternative GR with an additional scalar field (phi). Other scenarios mentioned by Wang include cosmological constant, of course, quintessence, dilaton, axion, tachyon, phantom field, and Chaplygin gas. Like the last in the list, Wang's model offers unified description of both dark energy and matter in succeeding cosmological evolution stages, starting from the inflationary period. His action is this (it should appear in your browser).

In this model the universe is created from the instanton solution, discussed in a previous paper by the author, of field phi when the field is dropped in the left potential well for negative phi. During the period of exponential inflation lambda(phi) provides a large cosmological constant. The inflation ends dynamically when rho + 3p ~ rho_phi + 3p_phi increases from −2rho_phi to zero. A graceful exit from inflation is claimed. After inflation of the early universe the scalar field behaves like cold dark matter, and the universe expands according to 2/3 power law. It looks promising. We shall see whether these arguments will be substantiated by the cosmological community.

Light Particle in the Landscape

2006-01-25T17:16:00.000+02:00

The holiday season is well over and papers have appeared this month in the arXiv but I have not read any well. I noticed that Lubos Motl had carefully chosen the submission moment to get the number 001 for his paper with Arkani-Hamed, Nicolis and Vafa. Sure enough, it is now the beginning of the second century of quantum physics ;-) . Some comments of the paper were written by Jacques Distler in his blog on January 20. I try to get some idea of this (next month, I guess ... after getting rid of some aches). Very briefly, the authors conjecture an upper bound on the coupling of gravity with respect to gauge forces. This implies new physics beneath the Planck scale near GUT scale with a light charged particle.

Not unexpectedly, the string discussion between Lubos and Peter Woit is flourishing after Peter was interviewed by Susan Kruglinski of Discover Magazine. There are twenty two responses at the moment on Peter's blog. Enjoy!

Susskind's book on Cosmic Landscape

2005-12-27T14:13:00.000+02:00

I read Leonard Susskind's book The Cosmic Landscape String Theory and the Illusion of Intelligent Design. The book has triggered a lot of discussion and interviews in the blogosphere: Peter Woit, Lubos Motl (find title "Distasteful Universe and Rube Goldberg machines"), and Gerard 't Hooft. Many more here. As a slow writer I have little to add to these writings by the top guys. In six words: I would agree best with 't Hooft.

Yesterday there was at the arXiv a talk WaveFunction of the Universe on the Landscape, given last summer, by Laura Mersini-Houghton: Quoting from her Discussion Section: "We are still at a very preliminary level of understanding the underlying picture, therefore it may be early to anticipate whether the selection criterion for our universe will be postulated or derived by our physical theories. The purpose of the proposal discussed here is to offer a selection criterion for the landscape vacua which is derived from the dynamics of the wavefunction of the universe propagating on the landscape background."

After the reasonably good first two thirds but rather lengthy last third of Susskind's book I found it refreshing and encouraging to read Mersini-Houghton's paper.

December 12

2005-12-12T21:37:00.000+02:00

Just a few quotes from recent weeks' blogosphere.

Peter Woit:
Weinberg Goes Anthropic
November 4th, 2005

The Cosmic Landscape
December 7th, 2005
Susskind’s new book, The Cosmic Landscape: String Theory and the Illusion of Intelligent Design is now out.

David Gross Admits String Theory is in Trouble
December 9th, 2005

Jacques Distler:
Exotic Instanton Effects
December 09, 2005

I’ve been reading the recent Beasley-Witten paper on (new) instanton effects in string theory.

Lubos Motl:
Utter confusion
December 09, 2005

David Gross has not only organized the prestigious Solvay conference but he also summarized it by the following words published in one article and second article in New Scientist:

We don't know what we're talking about
We are much like the physicists in 1911 who did not understand radioactivity
We are missing perhaps something as profound as they were back then
The field is in a period of utter confusion

Peter Woit:
Wilczek Goes Anthropic
December 12th, 2005

December 1

2005-12-01T12:44:00.000+02:00

**A paper Dimensionless constants, cosmology and other dark matters by** Max Tegmark, Anthony Aguirre, Martin Rees & Frank Wilczek came out today, conveniently on the day of Beyond Einstein webcast, telling where we stand now in particle physics and cosmology. Rather than to try to summarize this excellent paper, which just has to be read, I give a quote from the conclusions: “…suggesting that nature must be devised so as to make mathematical physicists happy.”

November 28

2005-11-28T15:50:00.000+02:00

An interesting paper, somewhat off the main stream, is Differential Structures – the Geometrization of Quantum Mechanics by Torsten Asselmeyer-Maluga and Helge Rose. They ask what is the geometry of quantum mechanics. Finding the answer to this question would bring us to a unified theory of physics in terms of one entity alone, the four dimensional space-time manifold. Matter is characterized in this theory by the topology of three dimensional particles. The differential structure gives us two pictures of matter: geometrical and topological. The former is related to the change in the non-local,wave-like four dimensional connection and the latter to the local three dimensional singularities.

I try to give some idea of the first few pages of the paper. Manifolds are described by maps h from its subsets W to the linear space R^n with subsets U. A coordinate transformation between two charts is a map between subsets of linear spaces. The overlapping origin of two W's is mapped into two images U_ij = h_i(W_ij) and U_ji = h_j(W_ij). A coordinate transformation between two charts is a map between subsets of linear spaces, h_ij: U_ij -> U_ji. Two charts are compatible if U_ij, U_ji are open and the coordinate transformations h_ij, h_ji are diffeomorphisms. A family of pairwise compatible charts that covers the whole manifold is an atlas. Two atlases are equivalent if their union is an atlas. A differential structure consists of the equivalence classes of the atlases of a manifold. The number of differential structures from dimension 1 up to 11 are 1, 1, 1, infinity, 1, 1, 28, 2, 8, 6, and 992, resp. In dimension four there is an uncountable number differential structures for most non-compact four-manifolds (countable for compact).

The main hypothesis of the authors is that the structures of quantum mechanics are induced by the differential structure of the space-time manifold. To support the idea they prove a theorem in which they end up in Temperley-Lieb algebra. This algebra represents the set of operators of transitions of the differential structure of space-time. They end the paper with a comparison of their model with Loop quantum gravity, knots and links appearing in both. More papers are promised by the authors.

November 4

2005-11-04T07:44:00.000+02:00

Read how much Steven Weinberg has confidence about the multiverse and what to bet for it.

October 21

2005-10-21T15:49:00.000+03:00

Lubos Motl tells in his blog about a seminar given by Burt Ovrut at Harvard with the title Heterotic Standard Model. To many this has been good news.

Lubos also blogs an interesting popular article by Juan Maldacena, Illusion of gravity from the November issue of Scientific American. It is about holography in quantum gravity. Having read it I could not conclude for sure whether this article, written in brilliant style, is good news.

Florian Gmeiner, Ralph Blumenhagen, Gabriele Honecker, Dieter Lust, and Timo Weigand have written the paper One in a Billion: MSSM-like D-Brane Statistics, claiming that a Standard Model-like configuration with three families of quarks and leptons in this class of models is statistically highly suppressed.

September 15

2005-09-15T18:46:00.000+03:00

N. Mankoc Borstnik and H. B. Nielsen have written a paper with a (too) long name but a very interesting first page third paragraph: "In an approach by one of us it has long been the wish to obtain the gauge fields from only gravity, so that ”everything” would become gravity. This approach has taken the inspiration from looking for unifying all the internal degrees of freedom, that is the spin and all the charges, into only the spin. This approach is also a kind of the genuine Kaluza-Klein theory, suffering the same problems, with the problem of getting chiral fermions included, unless we can solve them." Since I cannot judge their technical success you have to read the paper if interested.

September 13

2005-09-13T11:48:00.000+03:00

Robert H. Brandenberger tries to Look Beyond Inflationary Cosmology. Quoting him freely: Scalar field-driven inflationary cosmology suffers from serious conceptual problems many of which relate to ultraviolet issues it is likely that the same new fundamental physics required to address the ultraviolet problems of the Standard Model.

Since the paper is a conference contribution he lists the conceptual problems of conventional scalar field-driven inflation. The first problem, the amplitude problem, relates to the amplitude of the spectrum of cosmological perturbations. A more serious problem is the trans-Planckian problem: all scales inside of the Hubble radius today started out with a physical wavelength smaller than the Planck scale at the beginning of inflation. A third problem is the singularity problem. Recently, the singularity theorems have been generalized to apply to Einstein gravity coupled to scalar field matter where a past singularity at some point in space is unavoidable. The Achilles heel of scalar field-driven inflationary cosmology is the cosmological constant problem.

Then he goes over to suggest solving these problems using string theory.

An immediate problem which arises when trying to connect string theory with cosmology is the dimensionality problem. The moduli fields must be stabilized. Resolving the singularity problem is another of the main challenges. One must also solve the flatness problem. Finally, there must a mechanism to produce a nearly scale-invariant spectrum of nearly adiabatic cosmological perturbations.

The way to attack these problems is to focus on symmetries and degrees of freedom which are new to string theory (compared to point particle theories). The symmetry he makes use of is T-duality, and the new degrees of freedom are string winding modes.

Postulating that T-duality extends to non-perturbative string theory leads to the need of adding D-branes to the list of fundamental objects in string theory. With this addition, T-duality is expected to be a symmetry of non-perturbative string theory.

My comments: The role of UV problems in going beyond current theories has been known for long. In this paper the known issues of cosmology are traded for new questions in string/brane cosmology. This is how progress is usually made, provided the new problems can be solved. We remain to wait with interest.

September 12

2005-09-12T22:57:00.000+03:00

BBC Monday, 12 September 2005, 18:03 GMT 19:03 UK
http://news.bbc.co.uk/1/hi/sci/tech/4237800.stm

Most distant cosmic blast sighted

GRB 050904, Dr Daniel Reichart

Astronomers have witnessed the most distant cosmic explosion on record:a gamma ray burst that has come from the edge of the visible Universe.The blast was observed by the Swift space telescope and by a number of ground-based observatories.

The latest, record gamma ray burst was detected on 4 September 2005 and lasted about three minutes. It probably marked the death of a massive star as it collapsed into a black hole. It has a redshift of 6.29, which translates to a distance of about 13 billion light years from Earth.

August 29

2005-08-29T17:30:00.000+03:00

Tirthabir Biswas, Anupam Mazumdar and Warren Siegel analyze in their paper Bouncing Universes in String-inspired Gravity interesting cosmological questions by putting together general relativity, Newtonian gravity, inflation, Yang-Mills field theory and string theory.

They start by adding to the Einstein-Hilbert action an infinite sum of higher order derivative terms (Eqn. (1.5)). They find approximate and exact solutions such that that (i) the action can give rise to a ghost free and asymptotically free theory of gravity, and (ii) bouncing cosmological solutions for this type of actions.

In the usual FRW cosmology, it is the attractive force of gravity which makes the universe contract, eventually to a singularity. Now in the presence of asymptotically free gravity spacetime contracts but the internal pressure of matter resists, therefore causing the universe to bounce from the contracting phase into an expanding one (Eqn. (4.6), hyperbolic cosine bounce). Their cosmological constant is mainly required for the late-time consistency for their bounce ansatz (4.6), it is not necessary for having a bounce. They argue that its absence solves the graceful exit problem.

They divide the evolution into two distinct regimes: (i) near the bounce when the higher curvature terms dominate the evolution (ii) away from (both before and after) the bounce when the higher order terms can be ignored as compared to ordinary gravity and there is normal FRW evolution. They say they are unable to clearly identify a connection of these constraints to the necessity or sufficiency of asymptotic freedom. The write the most likely reason is that they only looked at a very specific bounce solution, namely the hyperbolic cosine bounce, and therefore are missing more complicated bounces which may be present in some of the asymptotically free theories. "We reserve a more detailed study of these issues to future research." The transition from the bounce should lead to a radiation dominated epoch before and after the bounce. During these phases, they claim to have ordinary gravity coupled to an ideal gas of matter/radiation fluid satisfying the usual omega, rho and Hubble equations (Eqn. (5.13)).

I find the paper very inspiring. A number of interesting calculations have been performed. Perhaps I have not grasped it right so I ask is the addition of higher (infinite) order derivative terms in the Einstein-Hilbert action something like adding resonances and Regge poles (in the 1960's) to get the full amplitude. What would the proper duality entities be, and the relationship between them? I do not have the answer but my favorite thought is in the direction of preons having color-like interaction near Planckian distances (there is only an uncompleted manuscript of it, which only Peter has seen, and one withdrawn from arxiv last year).

August 25

2005-08-25T13:54:00.000+03:00

A. Bouchareb, M. Ramon Medrano and N.G. Sanchez have studied Semiclassical (QFT) and Quantum (String) Rotating Black Holes and their Evaporation. Quoting freely, the authors compute the quantum emission cross section of strings by a Kerr-Newman black hole. In the early stage of evaporation, the string cross section shows the Hawking part of the emission with temperature Tsem, the semiclassical regime. For Tsem → Ts, the massive string modes dominate the emission, the string cross section shows a Hagedorn phase transition at Tsem = Ts. The last state of evaporation of a semiclassical Kerr-Newman black hole with mass M > mPl, Tsem(J,Q) < Ts, angular momentum J and charge Q is a string state of string temperature Ts, string mass Ms, J = 0 and Q = 0, which decays by the usual quantum string decay into all kinds of particles. Besides the classical/ semiclassical known bounds on J and Q, new bounds emerge in the quantum string regime.

A central object is ρ(m, j), the microscopic string density of states of mass m and spin mode j. They find for the extremal string states j → m^2α′ , a new phase transition at a temperature Tsj = sqrt(j/h)Ts, higher than Ts. They call it extremal transition. The characteristic behavior of this transition is a square root branch point near Tsj . It manifests as a logarithmic singularity in the string entropy S(m, j). This extremal behavior is universal and is analogous to the transition found for the thermal self-gravitating gas of point particles and for strings in de Sitter background.

By identifying the semiclassical and quantum (string) gravity regimes, the authors find a new formula for the Kerr black hole entropy Ssem(M, J), which is a function of the usual Bekenstein-Hawking entropy S(0)sem. For M ≫ mPl^2 and J < GM^2/c, S(0)sem is the leading term of this expression, but for high angular momentum a gravitational phase transition operates and the whole entropy Ssem is drastically different from the Bekenstein-Hawking entropy S(0)sem. This new phase transition takes place at a temperature TsemJ = sqrt(J/h)Tsem, higher than the Hawking temperature Tsem.

2005-08-25T09:22:00.000+03:00

Haloscan commenting and trackback have been added to this blog.

August 13

2005-08-13T13:40:00.000+03:00

Read "Rumors of new forces" at Sean Carroll's blog. Its an experiment by Eric Adelberger's group at the University of Washington.

August 12

2005-08-12T14:32:00.000+03:00

At Strings2005 (and many times before that conference!):"Is there any experiment which would falsify the theory?" Paul Frampton seems to give the first answer: an experiment involving a Josephson junction may detect the effect of dark energy, by observing a cut-off in the frequency of zero-point oscillations at about 1.7 THz. If such a cut-off were discovered, the consequences would be far reaching including the possible demise of the string landscape.

July 26

2005-07-26T15:26:00.000+03:00

Read The case for background independence by Lee Smolin if you want to find out who was smarter, Newton or Leibniz, as a relativist. Smolin writes also about relationalism, reductionism, natural selection, and hidden variables.

July 25

2005-07-25T13:51:00.000+03:00

Now the String 2005 is over. Instead of clear-cut conclusions it has triggered long discussions in the blogs of Peter Woit and Lubos Motl and also in the Cosmic Variance by Sean Carroll. This is somewhat confusing ... have a long break to get into these interesting writings - too long and involved to be commented here!

July 12

2005-07-12T14:12:00.000+03:00

While looking for the results of the Strings 2005 conference it was enjoyable to read an essay Micro-Anthropic Principle for Quantum theory by Brandon Carter.

June 28

2005-06-28T13:28:00.000+03:00

For summer fun and use read the blogs of Peter Woit and Lubos Motl, say between May 29, 2005 and June 26.

May 26

2005-05-26T07:55:00.000+03:00

Ben Freivogel, Matthew Kleban, Maria Rodriguez Martinez, and Leonard Susskind have written a paper Observational Consequences of a Landscape.

They write: "The string theory landscape of metastable de Sitter vacua is extremely rich. So many vacua exist that the large numbers can compensate the apparent fine-tuning of the cosmological constant, the gauge hierarchy, and whatever additional fine-tunings are phenomenologically required by observational data. Specifically we assume a large set S of minima consistent with the standard model and the small measured cosmological constant."

They squeeze out a number 10% that the actual number of efolds is between 62 and 64 with the observed bound being 62. Their opinion is that the observed suppression of the quadrupole and octopole anisotropies, seen by WMAP, should not be quickly dismissed as cosmic variance accidents.

It seems that the scientific and anthropic landscape paradigm string theory camps are drifting apart. Does one or the other (or both) have some of the fundamentals wrong? Do we have to be prepared to reevaluate where the limits of human scientific knowledge are.

May 22

2005-05-23T13:30:00.000+03:00

"Game over", or revival of (S) Matrix Theories

Current blog discussions remind me of the good old 1960's when (perturbative) field theory was considered useless in dealing with the hadronic interactions. A fundamentally different candidate theory, based on agreeable mathematical concepts like analyticity and unitarity, and called the

S-matrix, or bootstrap theory or nuclear democracy, was advocated vigorously by many prominent physicists. Soon, during the next decade field theory took its position back in the form of Yang-Mills theories where new type of particles, quarks and yet to be discovered scalars, play central role.

Today, doubt is cast over the by now traditional theories, the Standard Model, by the string theory camp for one. This new theory does not overthrow the old, rather it gives it as a low energy limit. Quantum gravity is the major issue. It seems as if mathematical elegance is again used as a method for searching new physical theory and the strings and branes are the new kind of "particles", though they have no experimental support like the quark model had even in its early form in hadron spectroscopy.

My way of thinking is that instead of one or two we, in principle, have many candidate theories including deterministic (April 27, 2005), condensed matter-like, Loop Quantum Gravity, string/M/K (or as one opponents call it, " non-predictive", (May 18 and back) and Noncommutative Geometry theories. Some of them are mutually exclusive (or disfavored), some not. Historically, string theory came about from the S-matrix (Veneziano) theory, so it seems like matrices are looking for a second chance to beat field theory, with the name S-matrix now replaced by just M or Matrix. And "nuclear democracy" being replaced by "brane democracy". - For amusing historical notes on matrices in physics in the 1920's, read this (May 9).

Among the problems in string/M theory are the vacuum and the singularities in Big Bang. They are discussed by Lubos Motl (May 15 and 16, 2005), based mainly on talks in the Conference at Columbia on May 13. Lubos Motl continues his analysis of landscapes' nature on May 21: it's infinite ... "Frankly speaking, the number of vacua has always been infinite." He discusses the stabilization of moduli, referring to a recent paper on Type IIA Moduli Stabilization, with comments from the authors, DeWolfe & al. (who quote for help Florence Nightingale - not Nightengale ;-) ), concluding that stabilization works in the case studied. (It is not widely known that FL was well trained in math, too!)

May 18

2005-05-18T11:08:00.000+03:00

Peter Woit (May 17, 2005) criticizes the talk of Nima Arkani-Hamed at Pheno05 at UW-M . Checking the original paper by N. A.-H. and Savas Dimopoulos I would rather say that this kind of "orthogonal" thinking should be welcomed rather than condemned.

May 17

2005-05-17T17:04:00.000+03:00

Two interesting papers, the first giving reference to the third below, appeared today on the connection between Supersymmetric Yang-Mills and the Quantum Hall System:
A. Ghodsi, A. E. Mosaffa, O. Saremi, and M. M. Sheikh-Jabbari, LLL vs. LLM: Half BPS Sector of N=4 SYM Equals to Quantum Hall System,
Brian P. Dolan, N=2 Supersymmetric Yang-Mills and the Quantum Hall Effect, and
David Berenstein, A matrix model for a quantum hall droplet with manifest particle-hole symmetry.
Frankly, I cannot say much more of them than is "emergence" emerging? Lubos will give soon a deep analysis, I believe ;).

May 4

2005-05-04T08:37:00.000+03:00

From time to time a student or teacher (or a retired physicist) wants to consult a well written review, with a solid introduction and summary, of a subject of current interest. On the AdS/CFT correspondence and related questions the thesis of Ian Swanson, Superstring holography
and integrability in AdS_5 x S^5 seems to fulfill such a need.

April 27

2005-05-02T09:09:00.000+03:00

The question of "playing dice" pops up every now and then. 't Hooft has inspired many people like M. Blasone, P. Jizba, and H. Kleinert who wrote Quantum Behavior of Deterministic Systems with Information Loss. Path Integral Approach. They have utilized the Faddeev-Jackiw treatment of singular Lagrangians which entirely obviates the need for the Dirac-Bergmann distinction between first and second class, primary and secondary constraints used in their earlier work. Finally, the authors conclude: "Our result supports the strong version of the holographic principle [6], namely that while deterministic degrees of freedom of a system scale with the bulk, the emergent quantum degrees of freedom (i.e., truly observed degrees of freedom) scale with the surface."

April 13

2005-04-13T22:01:00.000+03:00

Rafael D. Sorkin's Ten Theses on Black Hole Entropy struck me as very fundamental, and beautifully written. I even got a crazy idea what the bits of information could be. I just have not succeeded anybody else to get interested.

March 24

2005-03-24T16:45:00.000+02:00

Bj in Helsinki

Every now and then we get outstanding visitors coming to Helsinki in winter time. Today we had James Bjorken, giving a talk on The Classification of the Universes that was of great interest to many of us. I took some pictures in bj's seminar.

March 18

2005-03-18T16:49:00.000+02:00

The most interesting paper in some time is in my opinion (ok, this is very subjective as you see below) Quantized tension: Stringy amplitudes with Regge poles and parton behavior, by Oleg Andreev and Warren Siegel.

For now being out of town, I only comment the first and last paragraph. The first paragraph refers to the nostalgic time of the late sixties and early seventies, when I did some modest phenomenology in all the four regions of phase space. The last paragraph contains an idea "...that gravity would disappear at short distances ..." that came to my mind in August 2004 (hep-ph/0210446 v5 16 Aug 2004, still under low priority debug and upgrade) - and perhaps in raw form two years earlier. Whether the idea is correct ... who knows.

The real content of Quantized tension is, of course, in the paragraphs between and requires some more reading, and it is most likely subject to (rapid?) further development.

March 10

2005-03-10T14:42:00.000+02:00

At Aspen in February, Mirjam Cvetic gave a talk on particle physics
based on Intersecting D-branes. She claims progress being made. But they can't get "the devil from details": Higgs, chiral exotics.
More discussion on Higgs is given by Jesse Thaler and Itay Yavin.

March 9

2005-03-09T21:43:00.000+02:00

March

E. Witten has brought some long ago developed mathematics (by Roger Penrose) on the arena of the string theory, the twistors. This has stimulated many authors for further work. There has been Twistor Strings Workshop in Oxford in January 2005. Among the speakers were both Penrose and Witten. My view is that Sir Roger does not mind computing graviton and gluon scattering using twistors, but he is worried of problems on even more fundamental level. He has a new book The Road to Reality, which has been criticized by Frank Wilczek and, more favorably, by Peter Woit.

January

V. Braun, Y-H He, B. Ovrut and T. Pantev make a step toward string phenomenology in A Heterotic Standard Model.

Year 2004

Andrei Linde and coauthors have found the landscape's beauty attratctive. They state that "... some of the surprising properties of our world might arise not through pure chance or miraculous cancellations, but through a natural selection mechanism during dynamical evolution."

P. Brax, C. van de Bruck and A.-C. Davis have written a very readable (" ... get a feeling of the physics ... " ) review (cover page only on this site) of Brane World Cosmology (total 57 pages, 6 figures), and start your own "brane wars".

A. Ashtekar and J. Lewandowski have prepared a pedagogical status report titled Background Independent Quantum Gravity: A Status Report (125 pages, 5 figures).

Elias Kiritsis has written an interesting rewiew D-branes in Standard Model building, Gravity and Cosmology (132 pages, 7 figures).

A quick look at some late summer papers:

C. Burgess, Inflatable String Theory? This review consists of 15 well written pages.

T. Banks, W. Fischler, L. Manelli, Microscopic Quantum Mechanics of the p=rho Universe. This paper has to be read carefully, or be set aside for future measures.

More of strings, branes and tachyons:

A. Sen, Tachyon Dynamics in Open String Theory.

D. Klemm, Black Holes and Singularities in String Theory .

C. Kokorelis, Standard Model Building from Intersecting D-Branes .

H. Nilles, Five Golden Rules for Superstring Phenomenology .

After the above papers on theory and model building it's interesting to read M. Dine who writes that a large group of people have found "... at the very least, .. a very large elephant in the closet".

T. Banks is skeptical about the Landscape.

R. Bousso discusses the deeper questions of string Cosmology and the S-matrix.

Year 2003

See my web site.