Magic Monday Journal Club

1st September 2014

Back to the  main page


What a cute MMJC. Was really a nice moment to meet all of us after such a looooong absence. Your both magician are (and will be) traveling a lot this end of the year. However, we will do our best to keep a regular meeting as our field evolves very fast recently, and we really need to follow it.. Here are the articles we discussed on the 1st of September.

Dark matter searches going bananas: the contribution of Potassium (and Chlorine) to the 3.5 keV line

by T. Jeltema and S. Profumo

The paper analyzes  XMM observations of the Milky Way center and does not find any dark matter emission x-ray line.  It argues that all spectral features near 3.5 keV are accounted for if Potassium XVIII lines at 3.48 and 3.52 keV. The same lines can also explain the observed 3.55 keV dark matter signal in galaxy clusters, as long as their of these lines are allowed to vary freely in the fit (rather than constrained by the measured strength of other lines). You can  find comments on the subject in this blog.

Consistent Use of the Standard Model Effective Potential

by  A. Andreassen,  W. Frost  and M. D. Schwartz

The paper discussed the subtleties related to the gauge variance of the effective Higgs potential in the SM. It gives a prescription how to calculate a value of the potential at  a minimum in gauge invariant way. Applying this prescription  to the SM changes slightly (by a few hundred  MeV) the limiting Higgs mass below which our vacuum is metastable.You can find an annotated version of the paper there.

Non-Detection of X-Ray Emission From Sterile Neutrinos in Stacked Galaxy Spectra

by Michael E. Anderson, Eugene Churazov and Joel N. Bregman

One more paper in the raging war between pros and cons 3.5 keV lines.. So many articles these days that we are not really sure where to look about even if I have my personal impression on the subject. For people who do not follows all the story, we will make a little summary in the «popularization» section soon. So, what’s new in this work? Mainly that the authors looked in different galaxies observed by XMM and Chandra (and not only the dwarf one) and seem to find no evidence for a 3.5 keVish line. For the running (wo)men, you can just go directly to their Fig.4 which summarize well there results. They rule out the hypothesis of a 7.1 keV sterile neutrino with mixing angle fitting the Bulbul and Boyarski analysis at more than 3 sigma for both experiments. Notice that their work only concerns sterile neutrino model and NFW profile (not sure so valid one in the case of warm dark matter by the way)   The annotated version of the paper can be found around there.

Fitting the annual modulation in DAMA with neutrons from muons and neutrinos

by Jonathan H. Davis

At least.... At least an astrophysical explanation for the soooooo long claimed DAMA signal.. We were desperate. Indeed, the only available proposition, just after the release of the first DAMA results was the possibility that muons produced by cosmic rays and interacting with particles from the shield (extracting a neutron, indistinguishable from a dark matter candidate) in the atmosphere can account for the modulation. Indeed this flux depends on the temperature of the atmosphere. The colder is the temperature, the more collision of the parent particle exists and so less muons (coming from the decay of the parents particle). We then expect more events in July, 21st of July to be precise than in winter (DAMA bring near Roma, North Pole). However, the peak of DAMA is observed around beginning of June and thus, only muons cannot account for the total modulation. Davis had a great idea. He noticed that another event can produce neutron from the shield: neutrino interactions. For that, the neutrino should be energetic (above the MeV threshold) and then generated by boron 8 in the sun. The interesting feature of such a flux is that it is maximum when the earth is near the sun, so the 3d of December! It is them easy to understand that there exist a possibility, combining the two sources which have almost opposite phases (one maximum end of June whereas the other maximal beginning of January) to fit the DAMA signal. Davis succeed in it for a ratio of 10% of neutrino scattering. It's figure 1 summarize better than anything all my blabla. The amplitude should be realized in a volume of 1000m3 around the detector which is completely reasonable. At least, a nice alternative for the DAMA signal!! You can find an annotated version of the paper there.

First dark matter search results from the PandaX-I experiment

by PandaX collaboration

That’s it. China is on the race, and very well engaged. I think you should just directly go to the figure 6 of the paper to understand why.  Of course, you can tell «what for?» as you see that their results gives weaker bound than LUX or XENON100of a a factor 100. PandaX exclude DM with spin dependent cross section larger than 10-43 cm2 for a DM mass of 50 GeV wheres LUX already exclude cross sections as low as 10-45 for the same range of mass. However, do not forget that the idea (just the idea) of PandaX appear in 2010, a the time where XENON100 was already running. And the design of PandaX is such that they can increase their sensitivity just by... adding liquid Xenon in the  apparatus, nothing more. They gave the result for 17 days of data taking and 37kilograms of Xenon. What we can say, is that Chinese claims to be able to have the best world limits on this field in 2 years, and when we see how they run, I think we can trust them.....

A realistic assessment of the CTA sensitivity to dark matter annihilations

by Hamish Silverwood, Christoph Weniger, Pat Scott and Gianfranco Bertone

In this article, the authors remake a full analysis of the prospect of the future Cerenkov Telescope Array which should be operating in 2019-2020 (still in design phase). Whereas the north location has been found, the south part oscillate between chile or Namibia (in both cases, nice trip for conferences in perspective). They show that taking into account the galactic diffuse emission of photons and the cosmic ray background reduce significantly the sensitivity if the CTA especially when looking at point sources (see their Fig.3, where the reach for a thermal cross section is far from any hope!!). However using a "morpholigical method " (meaning selecting specific parts of the sky that they divided into pieces of puzzle), they increase sensibly the CTA sensitivity, especially around the galactic center as you can see in their Fig.6. Good job, and I guess several of these plots will be presented in conferences... An annotated version of the paper is available here.

Annihilating Asymmetric Dark Matter

by  Nicole F. Bell,   Shunsaku Horiuchi  and Ian M. Shoemaker

So, there was some excitation about the asymmetric dark matter idea some years ago. In this paper, the authors decided to see how is the exclusion/perspective to observe a dark matter candidate in asymmetric models through its annihilation in the Milky Way.The idea is quite simple. Asymmetric dark matter as a kind of two free parameter which is the relative density between the DM and anti-DM and the annihilation cross section. So, one can always permit higher annihilation cross section at the price to make the DM more asymmetric, and allowed some regions of light DM which were excluded by FERMI now avaiable. Have a look at their Fig.2 and you will understand everything. As a conclusion, it works, and you can have much higher sigmaV and yet not to be excluded by FERMI. Hurrah! You can find an annotated version of the paper there.

Superheavy dark matter and IceCube neutrino signals: bounds on decaying dark matter

by Carsten Rott, Kazunori Kohri, Seong Chan Park

Mmmmmm... This article is strange. Strange fir several reason. Firstly because I was working on similar subject when I read the title and first thought.. "Sh*t, I'm done like a rat" then I read it more carefully. And at the first sight when I watched at their equation (1) I thought "double holy sh*t" as it was really similar to what I was doing.. Except that.. Excepté that I think they missed the point. They just take a similarly see-saw model (more a toy model than a see-saw one by the way) just to justify a Dirac term of the form h nuL nuR justifying the decay of right handed neutrino into a Higgs and (monochromatic) left handed one, And then applying constraints from Icecube detector for very massive (above PeV scale) dark matter that you can find looking on their red curve of figure 2. Their constraints are quite strong, and in the absence of details concerning their analysis, adding to the fact that they find constraints 2 order of magnitude stronger than the official analysis of a Icecube for lower mass (when extrapolated), I have some little doubts about such results. In any case, still an easy paper to read during your breakfast time. look at the annotated paper there.