[astro-ph/0409275] Searching for a holographic connection between dark energy and the low-l CMB multipoles

Authors:  Kari Enqvist, Steen Hannestad, Martin S. Sloth
Abstract:  We consider the angular power spectrum in a finite universe with different boundary conditions and perform a fit to the CMB, LSS and supernova data. A finite universe could be the consequence of a holographic constraint, giving rise to an effective IR cutoff at the future event horizon. In such a model there is a cosmic duality relating the dark energy equation of state and the power spectrum, which shows a suppression and oscillatory behaviour that is found to describe the low l features extremely well. However, much of the discussion here will also apply if we actually live inside an expanding bubble that describes our universe. The best fit to the CMB and LSS data turns out to be better than in the standard Lambda-CDM model, but when combined with the supernova data, the holographic model becomes disfavored. We speculate on the possible implications.
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Jochen Weller
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[astro-ph/0409275] Searching for a holographic connection be

Post by Jochen Weller » September 24 2004

can somebody explain me how a future horizon can affect the CMB multipoles we
observe today ? I know this should come from the AdS/CFT correspondence when
applied to the whole universe. But this seems rather strange.

Further if we take their cut-off scheme for granted I find it unconvincing that the combination
of Fig. 1 (WMAP and SDSS) and Fig. 3 (SNe), leads to Fig. 5(WMAP, SDSS and SNe).
The two constraints (Fig. 1 and 3) look rather different and I am not sure if you should combine these then to get the tight constraint if Fig. 5 ?

Yours
Jochen

Constantinos Skordis
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Joined: September 27 2004
Affiliation: University of Cyprus

Post by Constantinos Skordis » September 28 2004

I don't think it necessarily affects the CMB today.
Presumably this occures because they impose a cutoff
in k-space.

A future horizon is like a never ending inflation. In other
words you have sub horizon modes becoming superhorizon
in the future. That by itself i think does not imply any
cutoff at any scale.

Now when you have both a past and a future horizon,
there would be regions of the universe which are never
observable at any time to some observer. (think of the
causal diamond). It was therefore thought that the
effective field theory of some fundamental theory which
give past and future horizons should exclude all modes
larger than the maximum possible size of the observable
universe. It is NOT implied directly from the
existence of horizons but rather was thought that it
should be true, because it would exclude unobservable
information from the theory.

So why (if one accepts the cutoff) should it appear to
us today? This would require fine tuning such that
the cut off is close to 1/H_0. If it was at smaller k
we wouldn't see it today and if it was at larger k
we wouldn't see any power at all down to smaller scales
(which is not true).

cheers,
-c

Carsten van de Bruck
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Joined: September 24 2004
Affiliation: University of Sheffield

Post by Carsten van de Bruck » September 28 2004

Constantinos wrote: [So why (if one accepts the cutoff) should it appear to
us today? This would require fine tuning such that
the cut off is close to 1/H_0. If it was at smaller k
we wouldn't see it today and if it was at larger k
we wouldn't see any power at all down to smaller scales
(which is not true).]

Its not really fine tuning if you accept their starting point:
the horizon (or the IR cutoff) in question is given by the volume
we will eventually see (given by the future event horizon). And
this horizon depends on the matter content in the universe. In
particular it depends on the equation of state of dark energy, etc.
From the theoretical point of view, this makes sense, I think: the
future event horizon limits the amount of information accessible.
But if this is really the way the holographic principle should applied,
I am not so sure.

Anyway, the future event horizon is automatically proportional to
1/H_0. The prefactor depends on the amount of dark energy, etc.
If you follow this up, its worth reading the original article by
Li (hep-th/0403127) and the first paper by Enqvist and Sloth
(hep-th/0406019).

Cheers,
Carsten

Jochen Weller
Posts: 45
Joined: September 24 2004
Affiliation: Ludwig-Maximilians-University Munich
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future horizon

Post by Jochen Weller » September 28 2004

OK I understand all that, but how does this work causally.
How do the perturbation modes today "know" about the future horizon.
In a closed universe this is much clearer to me, because there is a real cut-off scale.

A further problem I have
Imagine we are still in the matter dominated era in a flat universe, what would we imply then
for the cut-off scale ?
This seems strange.

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