On cosmology read Sean Carroll's paper Why is the Universe Accelerating? , dated October 13, 2003.
One of the originators of the holographic principle, Leonard Susskind has written an interesting paper The Anthropic Landscape of String Theory. Quote from his papers abstract: "The landscape of string theory vacua. Based on the recent work of a number of authors, it seems plausible that the lanscape is unimaginably large and diverse."
Quite recently Linde & al. wrote a paper Dark energy equation of state and anthropic selection. Quote from his papers abstract: "We explore the possibility that the dark energy is due to a potential of a scalar field and that the magnitude and the slope of this potential in our part of the universe are largely determined by anthropic selection effects."
The nature of the Big Bang classical and quantum initial singularity is discussed by M. Bojowald and H. A. Morales-Tecotl, Cosmological applications of loop quantum gravity. Quote (from p. 28) "In the Wheeler--DeWitt quantization the singularity problem has been glossed over by imposing initial conditions at a = 0, which does have the advantage of selecting a unique state (up to norm) appropriate for the unique universe we observe. This issue appears now in a new light because n = 0 does not correspond to a ``beginning'' so that it does notmake sense to choose initial conditions there. Still, n = 0 does play a special role, and in fact the behavior of the evolution equation at n = 0 implies conditions for a wave function [46]. The dynamical law and the issue of initial conditions are intertwined with each other and not separate as usually in physics. One object, the constraint equation, both governs the evolution and provides initial conditions. Due to the intimate relation with the dynamical law, initial conditions derived in this way are called dynamical initial conditions."
Occasionally theoretical physics papers can be from real life, as Carlo Rovelli's A Dialog in Quantum Gravity. The abstract reads as "The debate between loop quantum gravity and string theory is sometime lively, and it is hard to present an impartial view on the issue. Leaving any attempt to impartiality aside, I report here, instead, a conversation on this issue, overheard in the cafeteria of a Major American University."
Brian Greene, the author of The Elegant Universe (*), and Scientific American staff editor George Musser have had a very readable discussion article in the November 2003 issue of the magazine. Read Greene's last paragraph in the associated pdf-file.
Donald Marolf has written an excellent article on string theory resources including popular books, web sites, tehcnical papers and and confence proceedings - all one needs.
Lee Smolin and Artem Starodubtsev study
gravitational theories as constrained topological field
theories
using an action principle as the unifying factor. This paper is
climbing to the mountains of mathematics, yes mountain climbing is
exciting!
This paper by Smolin and Fotini Markopoulou, Quantum Theory from
Quantum Gravity looks to me much more interesting, check it!
There eg, the Planck constant h is a derived quantity,
as every reasonable person expects.
Very beautiful view of physics, and some of its history, is revealed by Peter Freund in a conference talk Physics and Geometry. Quoting his last sentence: "In fact force, matter, space and time, all the basic concepts, now determine each other and we face a unified whole". If only nature would know it ...
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.
V. Braun, Y-H He, B. Ovrut and T. Pantev make a step toward string phenomenology in A Heterotic Standard Model.
Page updated Jan 12, 2005; more in my blog.
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