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Super hubble and subhorizon fluctuations

  1. Mar 3, 2009 #1
    It is emphasized by Mr. bradenberger the concept of super hubble subhorizon fluctuations. I appreciate the idea that hubble radius and horizon are different ideas since they are physically distinct and partical horizon depends on the dynamics of cosmos evolution while hubble radius only depends on current state of scale factor. But when we talking about the metric fluctuation of a certain initial physical wavelength streches outside the hubble radius during inflation ,is it still inside the horizon?the answer is no if inflation have no start.But if before inflation there's an radiation of matter domination era, simple calculation shows up the the answer is yes.And the preinflation cosmic dominating guys should have an equation of state index bigger than 1/3,which is that for photon.Can there be something have EQS bigger than 1/3 and dominate the universe before inflation?
  2. jcsd
  3. Mar 4, 2009 #2


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    It would help if you gave an arxiv link to a relevant Robert Brandenberger paper. We aren't all familiar with the same papers, so giving a link can save everybody a lot of time

    In this case I suspect you may be referring to
    Alternatives to Cosmological Inflation
    but you might have a different one in mind and I'd like something definite.

    BTW if you too are thinking about alternatives to cosmo inflation, congratulations and welcome!
    Last edited: Mar 4, 2009
  4. Mar 9, 2009 #3
    thank you very much for citing this paper. I heard this idea in lectures given by him . In this paper it is depicted in fig 1. there was a radiation dominated era before inflation. it is this very era that keeps hubble radius and partical horizon coincide before inflation starts ,and partical horizon grows bigger than hubble radius once inflation starts. it there any evidence for this pre infation era of radiation domination? I think If preinflation era is dominated by some guy of EOS bigger than 1/3,then partical horizon will be smaller than hubble radius during this period, which generates a paradox. Since the phrase "perturbation with wave length of superhubble and subhorizon scale" may indicaes that partical horizon is always bigger than hubble radius.
    Yes, alternatives to inflation is a very interesting area to work on. I'm a graduate guy just started my research.And I'm on the edge of killing myself.We have just one year of graduate courework here and have little homework exercise to enhance our comprehension of foundamental theory.This make things very difficult for me since I was en engineering bachelor and trensfered to theretical physics looking for fun .Time and time again I feels the voids in my knowledge storage that hampers my research.And time and time again I was told that I need not to ask why but just follow the calculations is ok.
    I'm also interested in the decoherence of quantum fluctuations. But it seems that in some altanative scenario of inflation ,we need not quantum fluctuation to seed structure formation, just thermal fluctuation is ok , so we don't need to talk about decoherence at all.
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