September 15, 2005

September 15

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

September 13

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

September 12

BBC Monday, 12 September 2005, 18:03 GMT 19:03 UK

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.