[astro-ph/0508048] Did Boomerang hit MOND?

Authors:  Anze Slosar, Alessandro Melchiorri, Joseph Silk
Abstract:  Purely baryonic dark matter dominated models like MOND based on modification of Newtonian gravity have been successfully in reproducing some dynamical properties of galaxies. More recently, a relativistic formulation of MOND proposed by Bekenstein seems to agree with cosmological large scale structure formation. In this work, we revise the agreement of MOND with observations in light of the new results on the Cosmic Microwave Anisotropies provided by the 2003 flight of Boomerang. The measurements of the height of the third acoustic peak, provided by several small scale CMB experiments have reached enough sensitivity to severely constrain models without cold dark matter. Assuming that acoustic peak structure in the CMB is unchanged and that local measurements of the Hubble constant can be applied, we find that the cold dark matter is strongly favoured with Bayesian probability ratio of about one in two hundred.
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Scott Dodelson
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Scott Dodelson » August 09 2005

Quick question about these results: why is \Omega_{dm} =0.3 made up solely of neutrinos [so that \Omega_{cdm}=0] not allowed? I would think this would give a result very similar to the \Omega_{cdm}=0.3 and would show up in Figure 2 as \Omega_{cdm}=0.

Anze Slosar
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Anze Slosar » August 09 2005

Below are two CMB power spectra with all cosmological parameter set to their standard values but red is CDM no neutrions and green is the other way round + scaling so that the first peak matches. (They were produced by CAMB, the red is actually the default CAMB params.ini)

Image


In my understanding you need some cold gravitating component that doesn't see photons to raise the third peak. Does this answer your question?

Scott Dodelson
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Scott Dodelson » August 09 2005

Thanks Anze. Is it true then that another way to spin your results is that there is now [w/ Boomerang, but not with WMAP alone] a CMB-only constraint on neutrino mass? What is that constraint? Also, I would be interested in seeing the contours in [\omega_{cdm},\omega_{\nu}] space if you have them.

Carrie MacTavish
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Carrie MacTavish » August 09 2005

a CMB-only constraint on neutrino mass can be found in astro-ph/0507503. we get m_{\nu} < 1.0 eV (95% confidence limit) for the CMBall+B03 case. see figure 8 and table 5 of the paper. you can find a 2D contour plot (68% and 95% likelihood regions), for the CMB only case, in [\Omega_{cdm}h^2,\Omega_{\nu}h^2] space here:

http://www.cita.utoronto.ca/~cmactavi/CMBall_B03_neu.ps

Gil Holder
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Gil Holder » August 10 2005

I know that I took a course from Scott where I learned all of these things, but I am a bit confused. If we swap CDM for a single massive neutrino, then the neutrino mass should be on the order of 10 eV. Isn't this almost like CDM for CMB purposes? If matter-radiation equality is still at z=3300, then 10 eV is solidly non-relativistic at that point, and has been for a while.

I don't know exactly what Anze did, but I can produce curves that look like his if I leave the number of massless neutrinos as 3 and add 3 new massive ones. I think that choosing 3 massive neutrinos puts the transition to becoming non-relativistic in an interesting spot for the CMB for the chosen parameters. If instead you only have 1 massive neutrino (to make it non-relativistic earlier) but keep 3 non-massive ones (to keep matter radiation equality in the right spot) by allowing something like a light sterile (which you would probably need to get any sort of neutrino mixing scheme to even come close), the curves look better:
Image

All I think I did was set wcdm=0 and wnu=0.12 in params.ini and changed the number of massive neutrinos to 1 (and toggled to full integration of the neutrino phase space). Apparently there could be a contrived part (a new "just-so" neutrino solution?) of parameter space that is ok if you use only the CMB data. I thought all papers about all combinations of neutrinos and all combinations of data had already been written, so I find this surprising.

Alessandro Melchiorri
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Alessandro Melchiorri » August 10 2005

Hi all,

Thanks for your interest in our paper !
Few answers and comments:

1- To Scott: yes it seems that one can get interesting constraints on neutrino masses (considering them as 3 and degenerate) from CMB alone. I think the first paper to point this out is astro-ph/0409768. We discussed this in cosmocoffee and I was also quite skeptical but it seems to work... From beta decay we know that m_e<1.8 eV at 95 % c.l.. (see astro-ph/040845). In the case of 3 neutrinos, since mass differences are small, we get an upper bound of omega_nu (massive)<0.06. So all the discussion about saving MOND with massive neutrinos appears to me as not really interesting but, anyway...

2- To Carrie and Scott: the B03 upper limits have been obtained using the standard cosmological model. In the standard model also WMAP alone can put bounds on the neutrino masses as showed by astro-ph/0409768. In Anze's paper we have put bounds taking into account the possible inclusion of MOND in the formulation made by Bekenstein. As showed by Skordis et al. astro-ph/0505519 (BTW very nice paper) in those models the large angular scale CMB anisotropies are strongly affected by MOND. This may affect the standard constraints. Boomerang, VSA and others help in getting the standard constraints back since small scale CMB are less affected by MOND.

3- To Gil. Good point and nice plot ! yes it could be interesting to have a fourth sterile neutrino with such mass. But I think this would be too exotic in view of current neutrino oscillation results (see hep-ph/0405172) and it should be ruled out by LSS in the standard model. So CDM as neutralino is definitly a better dark matter candidate. Anyway experiments as LSND are suggesting this fourth neutrino... so interesting !

In our paper we were already considering such an exotic thing as modified newtonian gravity (...). In Mond scenarios (motivated by galaxy rotation curves) you like to have just standard particles as baryons and 3 (possibly massless) neutrinos. Otherways the price you pay is definitly too high !

BTW I think Anze's plot is with zero massless neutrinos and 3 massives.

Anze Slosar
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Anze Slosar » August 10 2005

Hi all,

Gill, yes your are correct and your point is a very intersting one. However, the entire idea of MOND was to get rid of the cold dark matter and explain everything with standard physics + modified inertia (and massive neutrinos are ok, as they belong to the "known" physics). A single massive sterile neutrino is heavy enough to be a good dark matter particle and this defies the main idea behind MOND which is to get rid of all dark-matter particles. And yes, you were correct to point out that I messed out the plot (it had 3 massless and 3 massive), but nevertheless it illustrated my point that if you don't have a non-relativistic component the third peak will be low... :)

BTW - it is still quite interesting, because your +1 massive neutrino is slightly different than CDM (because it is warmish?): it would be quite interesting to look for other signatures of such models, e.g. planck is bound to be able to distinguish the two curves...

I think Alessandro clarified other points quite well!

Simon DeDeo
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Simon DeDeo » August 10 2005

Am I right in understanding the detection here is coming from a shifting of z_eq and thus a boost in (what Scott in his book calls) the Early ISW effect?

I don't believe that the weak interaction of neutrinos with photons can affect anything as late as decoupling (as possibly suggested above.)

Gil Holder
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Gil Holder » August 11 2005

I think a lot of the neutrino mass detection must be coming from the shift in z_eq, as Simon suggests. I'm not sure what he is talking about on the weak interaction point, though. There is no way the neutrinos are having any interesting interactions at decoupling, so I hope it wasn't something I said that hinted at this.

To beat a dead horse:
A 10 eV sterile neutrino might not be ruled out by the galaxy clustering data, since the free-streaming cut-off is probably pretty close to the non-linear scale today. I figure the free-streaming length is somewhere on the order of a few Mpc.

The "model" is probably way off on the Ly-alpha forest, could be in trouble with clusters, and has huge problems forming galaxies. You would need to add some more epicycles to get anything reasonable. We're looking at a massive sterile neutrino, either MOND or some other thing to take care of galactic dark matter, a careful tuning so that the free-streaming scale is just barely hidden in the non-linearity, and we still have dark energy. Let's see the landscape explain this...

Anze Slosar
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Re: [astro-ph/0508048] Did Boomerang hit MOND?

Post by Anze Slosar » August 11 2005

Gil Holder wrote:
A 10 eV sterile neutrino might not be ruled out by the galaxy clustering data, since the free-streaming cut-off is probably pretty close to the non-linear scale today. I figure the free-streaming length is somewhere on the order of a few Mpc.

Well it looks even worse... I plot the matter power spectrum (I hope I hadn't messed up again, set 3 massless and 1 massive in the params.ini, accurate neutrinos and camb reports m_\nu=11ev, but the free-streaming length looks more like tens of Mpc on this plot, which looks slightly suspicious):

Image

Looks to me like galaxy clustering would have seen it as well, baryonic peak would change in amplitude, it would be the end of the world. The Viel et al paper [astro-ph/0501562] would have seen it by miles. Ah, bad luck, I was quite excited by that.

Gil Holder
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[astro-ph/0508048] Did Boomerang hit MOND?

Post by Gil Holder » August 11 2005

We seem to have hit on some ignorance on my part. I was figuring the free-streaming scale would be on the order of the horizon when T=m. That turns out to be a bad approximation. It gets the pre-factor right, but misses by a factor [2+ln(t_{eq}/t_{nr})] according to Kolb & Turner, which in turn apparently misses by another factor of 2. For the numbers here, this adds up to about a factor of 10, which puts the free-streaming scale indeed about where you show it, close to k_{eq}.

How do I reconcile this with the conventional wisdom that a high third peak indicates driven oscillations? They are initially driven, but hasn't the driving force free-streamed away? Maybe I should move this question to the dumb question section.

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