A Perspective on the Landscape Problem (15/2/12)

[marcus]

http://arxiv.org/abs/1202.3373
A perspective on the landscape problem
Lee Smolin
(Submitted on 15 Feb 2012)
I discuss the historical roots of the landscape problem and propose criteria for its successful resolution. This provides a perspective to evaluate the possibility to solve it in several of the speculative cosmological scenarios under study including eternal inflation, cosmological natural selection and cyclic cosmologies.
Invited contribution for a special issue of Foundations of Physics titled: Forty Years Of String Theory: Reflecting On the Foundations. 31 pages

The 40 Years of String issue of Foundations of Physics is being assembled and edited by Gerard 't Hooft and friends. It should be an interesting, possibly influential, collection of articles.

Here's the journal's home/index page: http://www.springer.com/physics/journal/10701

 

[marcus]

I'll look to see what other authors are contributing to the special String issue of the FoPh journal. One reason the journal interests me is that 't Hooft is listed as the Chief Editor. Maybe some of his vision informs the selection of authors and articles they have gathered. Erik Verlinde is a co-editor. Some of the other invited articles to be included in the special issue:
http://arxiv.org/abs/1103.3636 Steven S. Gubser
http://arxiv.org/abs/1108.0868 Carlo Rovelli
http://arxiv.org/abs/1105.6359 Steven B. Giddings
http://arxiv.org/abs/1112.0788 Michael J. Duff
http://arxiv.org/abs/1107.2897 Vijay Balasubramanian

When I looked just now at the Foundations of Physics website I saw that their current online bunch includes this by Louis Crane:
http://arxiv.org/abs/1006.1248
Holography in the EPRL Model
Louis Crane
(Submitted on 7 Jun 2010)
In this research announcement, we propose a new interpretation of the Engle Pereira Rovelli (EPR) quantization of the Barrett-Crane (BC) model using a functor we call the time functor, which is the first example of a co-lax, amply renormalizable (claren) functor. Under the hypothesis that the universe is in the Kodama state, we construct a holographic version of the model. Generalisations to other claren functors and connections to model category theory are considered.
[this is the revised abstract as groomed for publication, not the original arxiv version]
See http://www.springerlink.com/content/101591/?Content+Status=Accepted

http://www.springer.com/physics/journal/10701

 

[marcus]

Lee Smolin's take on the landscape problem involves a corrected prediction of 2 M_⊙ as upperbound on neutron star mass. In the present paper he cites this:
http://arxiv.org/abs/1012.3208
What a Two Solar Mass Neutron Star Really Means
James M. Lattimer, M. Prakash
(Submitted on 15 Dec 2010)
The determination of neutron star masses is reviewed in light of a new measurement of 1.97 M_⊙ for PSR J1614-2230 and an estimate of 2.4 M_⊙ for the black widow pulsar. Using a simple analytic model related to the so-called maximally compact equation of state, model-independent upper limits to thermodynamic properties in neutron stars, such as energy density, pressure, baryon number density and chemical potential, are established which depend upon the neutron star maximum mass. Using the largest well-measured neutron star mass, 1.97 M_⊙, it is possible to show that the energy density can never exceed about 2 GeV, the pressure about 1.3 GeV, and the baryon chemical potential about 2.1 GeV. Further, if quark matter comprises a significant component of neutron star cores, these limits are reduced to 1.3 GeV, 0.9 GeV, and 1.5 GeV, respectively. We also find the maximum binding energy of any neutron star is about 25% of the rest mass. Neutron matter properties and astrophysical constraints additionally imply an upper limit to the neutron star maximum mass of about 2.4 M_⊙. A measured mass of 2.4 M_⊙ would be incompatible with hybrid star models containing significant proportions of exotica in the form of hyperons, Bose condensates or quark matter.

The critical passage is on page 20. Based on new work by Lattimer and Prakash, if strange quark mass is tuned so that neutron stars contain kaon condensate then the UML (upper mass limit) on neutron stars is somewhere under 2 solar.

Otherwise, if kaon condensate does not form, neutron stars can be more massive. And indeed one has been found which has a preliminary estimate of 2.4 solar. This needs to be narrowed and confirmed but one can say that Smolin's evolutionary hypothesis is ALMOST refuted.
It would require that the quark mass be adjusted so that kaon condensate would form enabling a lower UML of 2 solar or less.
Lattimer Prakash's work caused this figure to be revised up from 1.6. Here is from page 20:

To maximize the number of black holes produced, the upper mass limit (UML) for stable neutron stars should be as low as possible. As pointed out by Brown and collaborators [30], the UML would be lower if neutron stars contain kaon condensates in their cores. That is,
UML_kaon < UML_conventional (1)
This requires that the kaon mass, and hence the strange quark mass be sufficiently low. Since none of the other physics leading to black hole production is sensitive to the strange quark mass (within the relevant range) cosmological natural selection then implies that the strange quark mass has been tuned so that neutron stars have kaon condensate cores.
Both the theoretical understanding of the nuclear physics of kaon condenstate stars and the observational situation has evolved since this prediction was published in 1992[31].
Bethe and Brown[30] argued that a kaon condenstate neutron star would have an U M L_kaon ≈ 1.6M_solar , so that is the figure I used initially. However, as emphasized recently...​