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From N-body simulation, the authors find that concentration-mass relation displays a turnover for group scale dark matter haloes, for the case of WDM particles with masses of the order ~0.25 keV. This may be interpreted as a hint for top-down structure formation on small scales. Is there any reionization mechanism in this scenario?

1)Because the size of the simulated boxes were ten times smaller in previous studies. 2)Weak lensing at scale below ~1arcsec could work. Their results might be helpful for estimating non-linear power spectrum based on a certain halo model.

Cooool. Was Malin there this morning? This could be right up her street, with her flexion stuff! Also, weak lensing at < 1" sounds a bit like strong lensing to me - I'll read the paper in detail and see if there's anything we can already say from our (admittedly modest) SDSS samples. Thanks!

Boylan-Kolchin et al identify a new problem with CDM at sub-galactic scales: the Aquarius simulated MW galaxy halos have subhalos that are about 5 times more massive than the actual dwarf satellites we see. Are we underestimating the MW satellites' masses somehow? Or is their something wrong with the simulations? Or both? Anyway, as Phil B said: add it to the list of things to investigate about CDM :-)

The observational counterpart? http://arxiv.org/abs/1111.2611

Interesting: Strigari & Wechsler prefer to state the problem as the sims predicting 25-75 times as many subhalos at the Fornax mass scale as are observed in the MW system - and in the paper you posted they look at thousands of MW analogs in the SDSS survey and find that the MW is not atypical. This strengthens MBK's conclusion, that there is a problem with CDM - although note that S&W put the emphasis on galaxy formation not being well understood at this mass scale. They imagine that there really are all those dark Fornaxes out there! Pretty cool - now, if we could just see them somehow...

Hezaveh et al simulate ALMA cycle 1 (ie 0.16" resolution) observations of Herschel/SPT sub mm lensed galaxies, and claim that the magnification is high enough, and the sources likely to be complex enough, to enable the detection of at least one DM subhalo of mass 10^8 or greater *in every system*

The current upper limit on the tensor-to-scalar ratio r is ~0.2, and should improve by an order of magnitude with future experiments. These authors claim that measuring the curl component of the lensing power spectrum of 21cm emission could yield incredible constraints r~10^(-9) (though this headline figure corresponds to their most optimistic case). The angular resolution of our planned 21cm telescopes is the crucial quantity in determining these constraints.

This is a very thought-provoking paper. At z=50 - the redshifted wavelength of HI is 21 cm * 51 which is 21m [about the length of a cricket wicket]. To image fluctuations you would need to space antennae by about half a wavelength, or by ~10 m. So far, so good, LOFAR is trying this already, filling many cricket pitches worth of land with antennae in Northern Holland. The UK even has its own little version at Chilbolton near Winchester. So far, so good. However, to get to r~10^-9 you need (apparently) to get to l_ max ~ 10^7, or an angular resolution of about 0.01 arcsec (Better than Hubble Space Telescope resolution). This means that, according to lambda/D, the total size of your 21-cm instrument has to have a diameter of ~ [21 m] / (10^-7), or ~10-times larger than the Earth. Of course, the atmosphere is getting close to opaque at these wavelengths, and the radio frequency interference is so bad that you'd want to put such an instrument on the back side of the moon. Unfortunately, the moon isn't large enough either, so you'd have to launch (or remotely deploy) something ~10-times the size of the Earth into deep space. This might be quite expensive, but in the SKA project we have most of the machinery to simulate such an instrument if any of you theorists out there are interested in collaboration.

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.

There's been quite a bit of discussion about this issue this summer, it came up at the Bologna dark matter meeting as well as the Aosta strong lensing workshop. Basically, in strong lens systems we infer *more* subhalos/satellites than CDM predicts for massive lens galaxies (the satellites cause "millilensing", where the quasar/radio source image fluxes are affected by the small amounts of additional magnification and demagnification). One suggested resolution to this problem is to include all the subhalos along the line of sight - Metcalf (2008) claimed this was the answer, and now Dan Dan Xu has tested this claim using the Millenium Simulation, and various assumptions for the satellite subhalo density profile.