Should have written a paper on it already ;-)

Like most of the experimental anomalies and surprises, the Fermi 130 GeV line has also come under dark shadows recently (http://www.newscientist.com/article/dn22466-doubt-cast-on-fermis-dark-matter-smoking-gun.html). It's not that I believed the dark matter interpretation of this line too much, but I still thought this would survive at least for a year ;) This so called game of town in particle astrophysics was initiated by Weniger in April 2012 with a detailed analysis of the publicly available Fermi-LAT data. This was followed by a series of papers from theorists with many well motivated models explaining the origin of this 130 GeV monochromatic line which apparently does not seem to have any obvious astrophysical origin. As the above link to the article in New Scientist says, the Fermi collaboration hasn't denied the presence of this peak in their data, but the dark matter origin of this line is in doubt as the same line is present even when the Fermi detector is pointed towards earth rather than the galactic center (where dark matter is more abundant). Hope Fermi collaboration would soon come up with an official publication telling us more about it. It won't be too much of a surprise if this goes away like B meson anomalies at DO/CDF went away in the wake of LHC results or the phantom of OPERA disappeared after the loose cable connection was found. Nevertheless, one obvious and immediate advantage of these anomalies is that theorists get a chance to write couple of more papers trying to fit their favorite theory or model with the data. Anyways, as someone pointed out correctly at the BENE workshop at ICTP, Trieste two months back, models don't get killed, they sometimes die out of starvation ;-)  So even if future Fermi-LAT analysis kills the dark matter interpretation of this interesting gamma ray line, all the models used to explain it already are still in safe heaven. Vive Le Model-Building! 

PS: For more information on this doubt cast on Fermi gamma ray line, see RESONANCE blog post!

FERMI does not confirm the rise in positron fraction with energy...:(

Today I saw a paper by W. de Boer titled "Indirect Dark Matter Searches in the Light of ATIC, FERMI, EGRET and PAMELA" (http://arxiv.org/abs/0910.2601). It is related to the Invited talk at SUSY09, the 17th International Conference on Supersymmetry and the Unification of Fundamental Interactions, Boston, 2009. The author gives a good comparison between the results from various experiments related to cosmic ray positron excess. I must say after looking at the FERMI results in this paper I am not that much enthusiastic about working on the dark matter interpretation of positron excess as I was when I first saw PAMELA results. The basic difference between latest FERMI data is that it does not confirm the peak in positron fraction at several hundreds GeV. The FERMI spectrum is more or less flat. The plot shown in the paper is as follows

The author has mentioned all the attempts so far for the positron excess explanation and commented that all the explanations seem correct and nobody can rule out any one of them. He has considered contribution of all such effects in the paper. I was particularly interested in dark matter interpretation of this excess which was quite interesting as well as challenging, since you need to make your particle physics model such that the proposed dark matter candidate unlike neutralinos annihilate primarily into leptons and not hadrons. Anyway as the author says we should wait for the future FERMI data which might focus more on possible dark matter link.

FERMI(GLAST) versus LQG-ists...

It was being speculated for a long time since the launch of FERMI (http://fermi.gsfc.nasa.gov/) that Lorentz Invariance Violation (LIV) which is an integral part of Loop Quantum Gravity(LQG) would be tested by FERMI data. I have never studied LQG. After going through first two three pages of Carlo Rovelli's book I had given up. Thus I have no idea how LIV comes out of such theories. Finally as it was expected, FERMI has got some data which apparently make LQG inconsistent. This is what a recent paper by FERMI collaboration titled "Testing Einstein’s special relativity with Fermi’s short hard γ-ray burst GRB090510" says. According to LQG photon speed v_ph is a function of its energy E_ph and can be very different from its low energy limit v_ph = c (E_ph -> 0) at enegies of the order fo Planck mass M_pl or say M_qg. Thus taking high energy photon data from Gamma Ray Bursts (GRB) and then noting down the variation of v_ph from c a lower limit can be set on M_qg. According to this latest paper FERMI data gives rise to the following limit M_qg/M_pl > 120 which contradictory to most quantum gravity scenarios where M_qg <~ M_pl. And it hardly makes any sense to talk about physics at an energy scale beyond Planck scale since at this scale gravity becomes so strong that everything collapses under gravity giving rise to a singularity. However these FERMI predictions may turn out to be wrong which would be a good news for LQG-ists obviously but as of now it seems they are in real trouble....;)