# Too Big to Fail?

1. Mar 6, 2014

### Chronos

This paper; http://arxiv.org/abs/1403.0954, Resonantly-Produced 7 keV Sterile Neutrino Dark Matter Models and the Properties of Milky Way Satellites, discusses how WDM can account for the dwarf galaxy deficit in galactic halos - otherwise known as the 'too big to fail' problem.

2. Mar 6, 2014

### marcus

The author Abazajian is someone to be aware of. He is junior faculty at UC Irvine and got PhD in 2001 and already has over 60 papers, with an AVERAGE citation count of over 100 per paper.
http://inspirehep.net/author/profile/K.Abazajian.1

And when you look at the list of people he has coauthored with it is pretty OK (to my limited ability to judge). and his specialty is listed as combined HEP-phenom & Astro/Cosmo, having worked with the SDSS (sloan digital sky survey). So it's the kind of person you might want to keep track of. If there IS something good about 7 keV sterile neutrinos this is the kind of young person who might be expected to jump on it.

I'll copy the abstract in part or full so we can have it in front of us and together think some about it.
http://arxiv.org/abs/1403.0954
Resonantly-Produced 7 keV Sterile Neutrino Dark Matter Models and the Properties of Milky Way Satellites
Kevork N. Abazajian
(Submitted on 4 Mar 2014)
Sterile neutrinos produced through a resonant Shi-Fuller mechanism are arguably the simplest model for a dark matter interpretation origin of the recent unidentified X-ray line seen toward a number of objects harboring dark matter. Here, I calculate the exact parameters required in this mechanism to produce the signal. The suppression of small scale structure predicted by these models is consistent with Local Group and high-z galaxy count constraints. Very significantly, the parameters necessary in these models to produce the full dark matter density fulfill previously determined requirements to successfully match the Milky Way Galaxy's total satellite abundance, the satellites' radial distribution and their mass density profile, or "too big to fail problem." I also discuss how further precision determinations of the detailed properties of the candidate sterile neutrino dark matter can probe the nature of the quark-hadron transition, which takes place during the dark matter production.
4 pages, 3 figures.

3. Mar 6, 2014

### marcus

It seems the first or among the very first to propose "warm" DM were Bode Ostriker Turok, who submitted a version of this paper in October 2000.
http://arxiv.org/abs/astro-ph/0010389
Halo Formation in Warm Dark Matter Models
Paul Bode, Jeremiah P. Ostriker, Neil Turok
(Submitted on 19 Oct 2000 (v1), last revised 29 May 2001 (this version, v3))
Discrepancies have emerged between the predictions of standard cold dark matter (CDM) theory and observations of clustering on sub-galactic scales. Warm dark matter (WDM) is a simple modification of CDM in which the dark matter particles have initial velocities due either to their having decoupled as thermal relics, or having been formed via non-equilibrium decay. We investigate the nonlinear gravitational clustering of WDM with a high resolution N-body code, and identify a number of distinctive observational signatures. Relative to CDM, halo concentrations and core densities are lowered, core radii are increased, and large halos emerge with far fewer low mass satellites. The number of small halos is suppressed, and those present are formed by top down' fragmentation of caustics, as part of a cosmic web' connecting massive halos. Few small halos form outside this web. If we identify small halos with dwarf galaxies, their number, spatial distribution, and formation epoch appear in better agreement with the observations for WDM than they are for CDM.
37 pages Published in Astrophysical Journal in May? 2001.

they actually CITE the January 2001 paper by Abazajian, Fuller, Patel
http://arxiv.org/abs/astro-ph/0101524
Sterile Neutrino Hot, Warm, and Cold Dark Matter
K. Abazajian, G.M. Fuller, M. Patel (Univ. of California, San Diego)
(Submitted on 30 Jan 2001 (v1), last revised 11 May 2001 (this version, v3))
We calculate the incoherent resonant and non-resonant scattering production of sterile neutrinos in the early universe. We find ranges of sterile neutrino masses, vacuum mixing angles, and initial lepton numbers which allow these species to constitute viable hot, warm, and cold dark matter (HDM, WDM, CDM) candidates which meet observational constraints. The constraints considered here include energy loss in core collapse supernovae, energy density limits at big bang nucleosynthesis, and those stemming from sterile neutrino decay: limits from observed cosmic microwave background anisotropies, diffuse extragalactic background radiation, and Li-6/D overproduction. Our calculations explicitly include matter effects, both effective mixing angle suppression and enhancement (MSW resonance), as well as quantum damping. We for the first time properly include all finite temperature effects, dilution resulting from the annihilation or disappearance of relativistic degrees of freedom, and the scattering-rate-enhancing effects of particle-antiparticle pairs (muons, tauons, quarks) at high temperature in the early universe.
24 pages, 8 figures, published PRD May? 2001

http://arxiv.org/abs/astro-ph/0106002
Direct Detection of Warm Dark Matter in the X-ray
K. Abazajian, G. M. Fuller, W. H. Tucker
(Submitted on 31 May 2001)
We point out a serendipitous link between warm dark matter (WDM) models for structure formation on the one hand and the high sensitivity energy range (1-10 keV) for x-ray photon detection on the Chandra and XMM-Newton observatories on the other. This fortuitous match may provide either a direct detection of the dark matter or exclusion of many candidates. We estimate expected x-ray fluxes from field galaxies and clusters of galaxies if the dark matter halos of these objects are composed of WDM candidate particles with rest masses in the structure formation-preferred range (~1 keV to ~20 keV) and with small radiative decay branches. Existing observations lead us to conclude that for singlet neutrinos (possessing a very small mixing with active neutrinos) to be a viable WDM candidate they must have rest masses < 5 keV in the zero lepton number production mode. Future deeper observations may detect or exclude the entire parameter range for the zero lepton number case, perhaps restricting the viability of singlet neutrino WDM models to those where singlet production is driven by a significant lepton number. The Constellation X project has the capability to detect/exclude singlet neutrino WDM for lepton number values up to 10% of the photon number. We also consider diffuse x-ray background constraints on these scenarios. These same x-ray observations additionally may constrain parameters of active neutrino and gravitino WDM candidates.
11 pages, 6 figures. published ApJ Oct? 2001

It looks like everything was set up and in place for a discovery, just waiting for the Bubul et al paper of February 2014 to announce an "unexplained 7 keV emission line" in the x-ray from various galaxies/clusters where you'd expect quantities of dark matter.

4. Mar 6, 2014

### marcus

To get the Bulbul et al paper, that broke the news, all you need to do is google "bulbul x-ray"

I think in Persian the word "bulbul" means nightingale (a type of songbird). I could be wrong. Anyway Esra Bulbul is a guy at Harvard-Smithsonian Center for Astrophysics and if you google "bulbul x-ray" you get
http://arxiv.org/abs/1402.2301

It's a paper that might turn out to deserve fame because it broke the news about observing 7 keV x-ray. If that turns out to be a dark matter signature.

5. Mar 7, 2014

### Chronos

Alexey Boyarsky, as well as Oleg Ruchayskiy have also been very active in this field. Examples include:

http://arxiv.org/abs/1001.0644
Searching for dark matter in X-rays: how to check the dark matter origin of a spectral feature

http://arxiv.org/abs/0906.1788
The search for decaying Dark Matter

http://arxiv.org/abs/0901.0011
The role of sterile neutrinos in cosmology and astrophysics

http://arxiv.org/abs/0812.3256
Realistic sterile neutrino dark matter with keV mass does not contradict cosmological bounds

http://arxiv.org/abs/astro-ph/0612219
Search for the light dark matter with an X-ray spectrometer

http://arxiv.org/abs/hep-ph/0601098
The masses of active neutrinos in the nuMSM from X-ray astronomy

6. Mar 7, 2014

### marcus

It's certainly exciting.
This 3.55 keV emission line is not the only unexplained radiation that people are studying as possible traces of decay of a dark matter particle. You probably noticed a recent posting by Doug Finkbeiner et al regarding some GeV radiation from regions where you'd expect DM. But that was not a *line*, the spectrum was more spread out.
and as I understand it that would probably involve assuming/inventing a NEW PARTICLE outside the conventional standard model.

This sterile neutrino idea is special (as I think you appreciated early on) because several things come together. There is room for it in the conventional standard particle framework. there is a funny gap in the standard menu where a particle like that ought to be. We don't need some exotic dispensation like "supersymmetry" for it. It belongs already.

And as Abazajian Fuller Patel asserted in 2001 (and your Boyarsky et al 2006-2010 papers confirmed) the early universe could have produced ENOUGH of that type that it could account for the dark matter. And the particles would be WARM (still moving fairly fast), which

as Turok and friends pointed out in 2000 would actually fit the data on satellite galaxies better, WDM is better than CDM for structure formation, or some people think so anyway.

So this may not be the RIGHT idea and it may eventually lose the Dark Matter sweepstakes, but this particle has 4 things going for it:

1. it fits in a conventional particle slot
2. early universe reactions could plausibly have made it abundant enough.
3. it would still be moving fairly rapidly (i.e. warm
4. an emission line at 3.5 keV seems to have been observed

7. Mar 7, 2014

### Chronos

Interestingly enough, this may not be the only dark matter signature. Juan Collar [U of Chicago], among others, has suggested heavier, more wimp-like particles may also stake a claim to membership in the DM particle family: http://clumma.newsblur.com/story/kaley-kerri-l-et-vir/a17bfe. A fair number of axion related claims have also surfaced in the last week. Incidentally, there is also a photo of Bulbul there. She is quite attractive. X-ray and gamma ray spectrography appears destined to become a hotbed of activity.

Last edited: Mar 7, 2014