Oxford astro-ph Coffee

Maybe an ACT insider could tell us more...

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.

Calculation to 2nd order of the effects of inhomogeneities on averaged observables.

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!

Authors: Lado Samushia,Beth A. Reid,Martin White,Will J. Percival,Antonio J. Cuesta,Lucas Lombriser,Marc Manera,Robert C. Nichol,Donald P. Schneider,Dmitry Bizyaev,Howard Brewington,Elena Malanushenko,Viktor Malanushenko,Daniel Oravetz,Kaike Pan,Audrey Simmons,Alaina Shelden,Stephanie Snedden,Jeremy L. Tinker,Benjamin A. Weaver,Donald G.

Massive Gravity is this year's must-have theory of modified gravity. The concept is simple - what if the graviton had a (very small) mass? However, building a consistent and viable theory from this idea has proved very difficult. It has now been achieved for the background-level cosmology, and can fit the accelerated expansion (with the usual fine-tuning problems, of course!) This paper takes the first steps towards the perturbation theory that needs to be developed if we are to test Massive Gravity with measurements of structure growth, etc.

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

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.

SPT lensing paper

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.

Astrophysics > Cosmology and Extragalactic Astrophysics Title: Large-Scale Structure with Gravitational Waves I: Galaxy Clustering (Submitted on 7 May 2012) Abstract: Observed angular positions and redshifts of large-scale structure tracers such as galaxies are affected by gravitational waves through volume distortion and magnification effects.

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.

Celia visited us for several months last summer - this paper is the outcome of her work here. In EBI gravity there is an 'Eddington-dominated' epoch in the universe prior to radiation domination, which can avoid the need for a big bang singularity. However, it turns out that tensor perturbations in this early phase are unstable. It's particularly interesting that the instability only shows up at the perturbative level, whilst the background cosmology remains non-singular.

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

This group continue Steinhardt and Turok's on going interest in cyclic cosmology by using an anti-gravity phase to resolve a crunch/bang transition.

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.

Axions are ultra-light particles that arise in string theory, and could make up some part of the dark matter in the universe. If so, what are the prospects for detecting their effects with galaxy surveys/CMB/weak lensing with future experiments? Come and ask the authors.

Pontzen and I were sitting there reckoning axions look a lot like hot dark matter - but I guess there must be some key difference at large angular scales to enable Dodi et al to distinguish between massive neutrinos and axions in a Planck+Euclid combo. Pretty cool :-)

Interpolation schemes for modelling the PSF, including some fun stuff like Gaussian Processes.

Now we need to get our paper out ASAP and start doing comparisons! :-) Re: "optimal" interpolation: I think they do a nice job of showing (and agreeing with us ;-) that you do best by having a very flexible, multi-scale model for the underlying maps. We also incorporate information about the statistics of the atmospheric PSF pattern in our prior; Kriging is more local, in that the covariance function is estimated only from the data in hand. Which makes me wonder what happens when the data sparseness goes up...