May 26, 2005

May 26

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 23, 2005

May 22

"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

, 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

May 18

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

May 17

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 04, 2005

May 4

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.

May 02, 2005

April 27

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."