As promised, I’m ready to provide a fuller report of the science at the meeting I was at last week - From Quantum to Cosmos: Fundamental Physics Research in Space, held by NASA at the Airlie Center in Warrenton, Virginia.
I mentioned last time …

I have several questions related to the finite or infinite issue which I am hoping a cosmologist could help answer.

1). The low CMB quadrupole is in sharp contradiction with the infinite universe prediction for the quadrupole. Wouldn’t any infinite universe model which tries to accommodate this observation be considered an unnatural stretch?

2). Luminet et al (2004) and Aurich et al (2005) and others have written highly critical papers regarding the topology conclusion reached by Spergel et al (2004). A lot of this criticism is two-pronged: they basically say that (i) the 1st year sky-maps have too much noise in them for Spergel et al to have reached the conclusion they did, and (ii), the methodology itself is in some way flawed. Who is correct? Do the WMAP 3-year sky-maps have a high enough signal-to-noise ratio for one to look for a topological signiture in them, or, will it take another satellite (i.e. the Planck Surveyor) to resolve this issue?

3). Do Spergel et al have plans to write a paper to counter the recent criticisms that have been leveled against their “circles in the sky” analysis?

We do freeze the power spectrum before we do the model fits. We basically
spent 2 years modifying the pipeline so that we could treat the noise properly
and pass various null tests and the self-consistency tests. We didn’t run
any serious cosmological models until about 3 months ago.

The foreground model for the temperature was indeed
fixed before the power spectrum was computed. The new foreground
model has only 2 free parameters— the big change was switching
from using the Haslam 408 MHz map to model the foreground
to using an internal combination of WMAP data (22 GHz-30 GHz).
When we were testing the foreground models, we used
the difference between 40 and 60 GHz power spectra as a test of the foreground model. Since this difference contains no CMB signal,
this fitting scheme is unbiased

The shift in l =3 and l=5 is due to switching from using the
MASTER algorithm to using Maximum Likelihood. George Efsthathiou
wrote a nice paper discussing this issue and we were convinced to
use ML analysis on the low l’s.

The improvement in chisq’ed was due to several effects:

- better beams– these were fit to Jupiter and had no free parameters
to “tweak”

- using smaller pixels in the map making

- an improved foreground model

I should note that we also have done blind tests on model fitting.

When we started this project, I never expected the data to fit the model
(I still dislike the cosmological constant), but we have to present what we find.

Constraining Strong Baryon-Dark Matter Interactions with Primordial Nucleosynthesis and Cosmic Rays

Self-interacting dark matter (SIDM) was introduced by Spergel & Steinhardt to address possible discrepancies between collisionless dark matter simulations and observations on scales of less than 1 Mpc. We examine the case in which dark matter particles not only have strong self-interactions but also have strong interactions with baryons. The presence of such interactions will have direct implications for nuclear and particle astrophysics. Among these are a change in the predicted abundances from big bang nucleosynthesis (BBN) and the flux of gamma-rays produced by the decay of neutral pions which originate in collisions between dark matter and Galactic cosmic rays (CR). From these effects we constrain the strength of the baryon–dark matter interactions through the ratio of baryon - dark matter interaction cross section to dark matter mass, $s$. We find that BBN places a weak upper limit to this ratio $

Hiranya - sorry to harp on #14 - as far as I know, cosmic variance ~ 1/sqrt(l(l+1)) - if this is true, then the width of the grey area should be less at l=200 than it is at l=100, but it actually seems to be thicker! Is this an artifact of the way the plots are made, or am I missing something? Again, sorry: I am a newbie!

Savya