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A new tool?

  1. May 13, 2006 #1

    wolram

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    http://arxiv.org/abs/astro-ph/0605278

    Searching for modified gravity with baryon oscillations: from SDSS to WFMOS
    Authors: Kazuhiro Yamamoto, Bruce A. Bassett, Robert C. Nichol, Yasushi Suto, Kazuhiro Yahata
    Comments: 16 pages, submitted to PRD

    We discuss how the baryon acoustic oscillation (BAO) signatures in galaxy power spectrum can distinguish the two different models to explain the cosmic acceleration, the modified gravity and the cosmological constant. For this purpose, we consider a model characterized by a parameter n, which corresponds to the Dvali-Gabadadze-Porrati (DGP) model if n=2 and reduces to a spatially-flat cosmological model with a cosmological constant for n=\infty. We find that the different expansion history of the modified gravity model systematically shift the peak positions of BAO. A preliminary analysis using the current SDSS LRG sample indicates that the original DGP model is disfavored unless the matter density parameter exceeds 0.3. The constraints will be strongly tightened with future spectroscopic samples of galaxies at high redshifts. WFMOS, in collaboration with other surveys such as Planck, will powerfully constrain modified gravity alternatives to dark energy as the explanation of cosmic acceleration.
     
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  3. May 13, 2006 #2

    marcus

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    Hi Wolram, personally I cannot understand this.
    don't seem able to get to square one with it.
    maybe someone else can.

    they seem to be comparing a BRANEWORLD :surprised
    scenario they call DGP
    against the more usual model with dark energy or positive cosmological constant.

    DGP means Dvali-Gabadadze-Porrati

    I usually don't bother with Braneworld scenarios because they don't strike me as Occam enough to be interesting. Too much junk. extra dimensions. If there was some NEED for extra dimensions that would be something else, but there doesnt seem to be any. My personal opinion of course but I think that
    in cosmology at least, the simpler 4D models are developing just fine.

    there is a group at Portsmouth with Roy Maartens that does quantum cosmology phenomenology-----they study how to TEST QUANTUM WORLD MODELS. that is commendable for sure, roy maartens is first rate, portsmouth is on the map and one of the coauthors of your paper is at portsmouth. So far so good.

    I guess the name of the game is you are supposed to be up for testing anything no matter how strange and if possible shoot it down. kill it before it multiplies.

    that seems to be what they are doing here in this paper. they say the Braneworld explanation of accerating expansion effects is 'DISFAVORED' by their analysis.

    You may have spotted a trend, Wolram. Thanks. At first i didnt realize it was going to be interesting. I will keep an eye out for more stuff like this.
     
    Last edited: May 13, 2006
  4. May 13, 2006 #3

    wolram

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    I had to google , Dvali-Gabadadze-Porrati , why are there no Toms ,Dicks
    or Freds, any way i could not tell by the words how thier test works, but if it
    is a step to killing this horrid thing fair enough.
     
  5. May 14, 2006 #4

    selfAdjoint

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    Yeah why? It's sure not the fault of the Dvalis, Gabadadzes, and Porratis of this world! Speaking as a guy named Dick.
     
  6. May 14, 2006 #5

    marcus

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    Father, forgive them their senses of humor
    [looks to the heavens]
     
  7. May 16, 2006 #6

    marcus

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    Hi wolram, I promised to keep a look out for this kind of thing. one came out today:

    http://arxiv.org/abs/astro-ph/0605371
    Using cosmology to constrain the topology of hidden dimensions

    Joan Simon (UPenn), Raul Jimenez (UPenn, OCIW), Licia Verde (UPenn), Per Berglund (UNH), Vijay Balasubramanian (UPenn)
    4 pages

    "A four-dimensional universe, arising from a flux compactification of Type IIB string theory, contains scalar fields with a potential determined by topological and geometric parameters of the internal -hidden- dimensions. We show that inflation can be realized via rolling towards the large internal volume minima that are generic in these scenarios, and we give explicit formulae relating the microscopic parameters (e.g., the Euler number of the internal space) to the cosmological observables (e.g., the spectral index). We find that the tensor-to-scalar ratio, the running of the spectral index, and the potential energy density at the minimum are related by consistency relations and are exponentially small in the number of e-foldings. Further, requiring that these models arise as low-energy limits of string theory eliminates most of them, even if they are phenomenologically valid. In this context, this approach provides a strategy for systematically falsifying stringy inflation models."

    the phenomenology brethren seem to busy themselves with ways to put brane and extra dimension to the test
     
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