From: Ariel Goobar (ariel@physto.se)
Date: Mon May 05 2003 - 00:06:17 PDT
Hi Rob,
Edvard Mörtsell and I adressed that issue in our JCAP paper
http://ej.iop.org/links/54/8NOGBZMksf8j,Akpvi0dsQ/jcap042003003.pdf
"A possible concern is what implications photon-axion oscillations can
have for the CMB observations. As noted by previous authors, assuming
that the magnetic fields form at relatively low redshifts, the
background radiation will be redshifted to such long wavelengths that
the effect will be negligible. This can be seen by studying
Eq.~(\ref{eq:rho11}) for small photon energies."
Cheers,
Ariel
On Sun, 4 May 2003, Robert A. Knop Jr. wrote:
> I don't know a whole lot about this topic, but here's a thought. Does
> anybody know what the limits from the CMB on these oscillations are?
>
> My simplistic thought on this:
>
> * The CMB is optically thick and a blackbody, thus we should know the
> flux emitted by it.
>
> * We know the angular diameter distance to the CMB, thus we know the
> luminosity distance to the CMB.
>
> * Therefore, we should be able to use flux measurements of the CMB to
> set limits on photons oscillating away into other strange things.
>
> Are there holes in this? E.g., would photon/axion oscillations also
> throw off our distance measurement? (I can't see how that would change
> the angular diameter distance.) How well calibrated is the absolute
> flux of the CMB? Enough to do anything useful with this?
>
> Given that the CMB is as far back as we can see photons at all, if we
> can use it as a "standard candle", given good flux measurements it
> should be able to provide the best possible limit on this. The only
> problem is that I don't really have a good idea about how well one can
> calibrate the absolute flux measurement.
>
> -Rob
>
>
-- ___________________________________________________________________ Ariel Goobar (www.physto.se/~ariel) Department of Physics, Stockholm University AlbaNova University Center, SE-106 91 Stockholm, SWEDEN tel: +46 8 55378659 fax: +46 8 55378601
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