# Some Recent Papers

### Year 2003

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 ...

### 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 2005

*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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