Oxford astro-ph Coffee

As soon as you move away from a perfectly homogeneous and isotropic cosmological model, what is meant by the "acceleration" of spacetime becomes ambiguous. It's important to be clear on what type of acceleration is being considered in any given observational or theoretical study, since different types can have very different cosmological implications.

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

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

First kSZ detection! From ACT and BOSS together.

Discovery of a very distant group of galaxies believed to be living in a M > 10^14 solar mass halo.

This work claims a 4-sigma detection of variation in the fine-structure constant over the sky and, furthermore, if a dipole form is assumed, a preference (also at 4-sigma) for evolution over cosmic time.

A sampler, new in both algorithm and code, from Hogg and co. They claim speed ups over Metropolis Hastings and easy shared-memory parallelism using an ensemble method.

A long paper on measures in Cosmology, which I haven't read in its entireity yet. However, I found the final comment in the abstract quite provocative and interesting: "In a universe where the second law of thermodynamics holds, one cannot make use of our knowledge of the present state of the universe to "retrodict" the likelihood of past conditions." This is due to laws being time symmetric, while in practice we have the second law. In practice we *must* resort to Occam's razor and/or beauty arguments. Later: "if one wishes to make an argument in favor of inflation having occurred in the early universe, this argument must be based upon its being a simple and/or elegant hypothesis that accounts for observed phenomena. Any argument about the "likelihood" of inflation based upon the Liouville (or other) measure on phase space will require a justification for the use of this measure." Sometimes, beauty and Occam's razor are incompatible, or rather scale dependent (as in the case of the string landscape), and from a purely philosophical point of view I don't feel entriely comfortable with either being used as a criterion of truth when trying to discover things about the universe. However, this paper makes this seem inevitable. Certainly food for thought.

This set of three papers (the link is to the first one, by Nikhil Padmanabhan) describes a factor of two improvement in the SDSS DR7 BAO distance estimate, just by improving the data analysis. Basically, non-linear gravitational collapse causes the usual BAO feature in the galaxy correlation function to appear smoothed out: it can be partially sharpened back up by using the Zel'dovich approximation to reconstruct the density field given the redshift and position data. The result is an increase in cosmological parameter accuracy roughly equivalent to surveying 3-4 times more sky. Software is vital!

It is interesting to see, in the third paper, how the constraints on H_0 \Omega_m space are robust to different scenarios of curvature and dark energy, and compatible with direct measurements of H_0. But also, as expected, this is effected by what one assumes about the neutrinos.

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

SPT lensing paper

Using N-body simulation, the authors showed that velocity-dependent self-interacting dark matter gives the inner circular velocity profiles of the most massive subhalos that are compatible with the data of the brightest Milky Way dSphs.

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.