Group items tagged

Our peculiar velocity with respect to the CMB rest frame can be measured through off-diagonal correlations in harmonic expansion coefficients due to aberration. The author shows that a new technique called "pre-deboosting" will work for detecting such correlations up to l~10000. If the measured residual peculiar velocity is different from the expected value, it would be a hint of some anomalies on superhorizon scales.

The statistical anisotropy of the mean of the CMB temperature fluctuations is tested. The naive inflationary prediction is that the mean a_lm's are zero, but the authors find a deviation from this expectation for l=221 - 240.

A neat paper demonstrating constraints on faster than light neutrinos using cosmological bounds on the number of effective relativistic species at BBN and at the CMB. For a simple Lorentzian tachyon there is an imaginary mass \mu, and an anergy dependent speed v(\mu,E)>1 (where c=1). The bounds on N_eff translate to bounds on the mass, and therefore bounds on the speed at different energies for this type of super-luminal neutrino. From the CMB the speed at OPERA energies (\sim GeV) is bounded to be v-1<10^{-23}ish, whereas OPERA claimed v-1\sim 10^{-5}. The constraint at \sim MeV is also tighter than SNe1987A constraints. These constarints further rule out explanation of the OPERA results with this type of neutrino. Even though I would not think OPERA is explained by anything like this anyway, I still think it is a simple and neat way to use cosmology. It would probably make a good problem sheet/exam question!

One of the interesting things about this paper, is that they have a modular code, StringFast which they release here: http://www.astro.ubc.ca/people/scott/stringfast.html

Nice to see our (Morganson et al, ref 17) lensing limit on the string tension (from not finding any sets of split pairs of faint blue galaxy images in the HST archive) is still competitive - its equal to the CMB limit they take as their best case scenario :-) Mind you, we could only rule out long straight strings.We could probably put some limit on their wiggliness parametr too I suppose - but its nice that the CMB power doesn't care about wiggliness or anything.

Perhaps an ACT team member could give us a verdict on this?

You can fix the acoustic scale using low-z luminosity distance measurements instead of the high-z CMB measurement. This would be a useful consistency test for LCDM, and can be used to constrain N_eff.

Does anyone understand what's new in this vs their previous work? Is this still just the affect of confusion over the TOD/pointing?

A recent-historical analysis of cosmological parameter estimation. "Of the 28 measurements of Omega_Lambda in our sample published since 2003, only 2 are more than 1 sigma from the WMAP results. Wider use of blind analyses in cosmology could help to avoid this."

Their detection of confirmation bias (aka unconscious experimenter bias, or groupthink) may not be so significant: most if not all of those Omega_Lambda measurements will have used WMAP CMB priors. Next step would be to try and correct for that. Their warning for future analyses is spot on though: parameter estimation needs to be done blind.

Point sources from the WMAP 7 catalogue are stacked, and the results are found to be consistent with the WMAP beam models. The correctness of the beam models used had been questioned by Shanks and others, who found that inaccurate models could introduce a significant bias into the measured CMB power spectrum. The authors here also find evidence for spectral steepening above 61GHz. This changes the estimates for the spectrum of unresolved point sources. Accounting for this effect, the primordial power spectrum seems to be closer to scale invariant than first thought.

Maybe an ACT insider could tell us more...

I'll let Phil do the talking on this one!

There is a discrepancy between cluster Y_SZ measurements made by Planck and AMI. Yikes!

Astrophysics > Cosmology and Extragalactic Astrophysics Title: First measurement of the bulk flow of nearby galaxies using the cosmic microwave background (Submitted on 6 Jul 2012) Abstract: Peculiar velocities in the nearby Universe can be measured via the kinetic Sunyaev-Zel'dovich (kSZ) effect.

The authors find a dipole in the variance of the Hubble flow, which they attribute to the effects of local structure. They find that local structure induces a ~0.5% variation in the distance to last scattering over the sky.

Another analysis of the kSZ signal in the WMAP data finds no evidence for Kashlinsky's claimed anomalous bulk flow.