Sunday, November 11, 2012

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 ( 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!

Monday, November 5, 2012

Looking for a common theme of work!

Pursuing research in an academic institute or university in India is not easy with so much teaching load as well as other administrative works. And probably that's the reason why most of the good research in India are carried out in special research institutes or laboratories where the teaching load is almost zero. This is quite a different picture compared to universities/institutes in other countries (developed ones, in particular) where most of the research output comes from universities. I don't know whom to blame for the poor research conditions of Indian universities, but hopefully the situation will change slowly with the central government authorities seem to be taking a series of initiatives. Anyways, without going further into the blame game, the best way is to make maximum use of the existing system and produce maximum possible quality output. In the physics department of Tezpur University ( where I work, there are around 16 faculty members working in different areas like nano-physics, astrophysics, high energy physics etc. The experimental people are comparatively more active in research as they have a large number of research students under their supervision as well as good number of equipments. Whereas, the members of the theory people do not have many students under them and so is the number of publications. Recently, we have decided to choose a common theme for the theory people so that the theory people can work together on it with a long run perspective. That should hopefully take some load of an individual faculty who do not have the "eligibility" yet to take students under him/her. Here "eligibility" doesn't refer to intellectual eligibility of course, but the "eligibility" criteria defined by the system here which I neither try to justify nor ridicule. But, choosing a common theme of work is not as easy as it may sound, since almost all of us had worked on quite different things during doctoral research. But looking at the fact that the present era is the era of inter-disciplinary research with people explaining condensed matter problems using theory of gravity (just an example), the possible options for such a theme should not be a scarcity.

The expertise the theory people here have are mainly neutrino physics, hadron physics, cosmology, astrophysics/astronomy and plasma physics. As a first trial, we are thinking of considering the problem of dark matter as a common theme (yet to be decided though). Since this is a huge research area, the general feeling is that it should touch upon the field of expertise of each one of us to some extent at least. To go ahead with this theme, it was necessary to highlight some of the interesting and recent things happening in this area to the members since not all of us are actively working on it. I gave an overview seminar on dark matter starting with astrophysical hints like galaxy rotation curve, bullet cluster, structure formation and then going into some details of particle characteristics of dark matter, direct/indirect experimental evidence highlighting many recent anomalies (130 GeV Fermi-LAT line for example) which indirectly point towards the existence of dark matter. Of course, in my ways of looking at this problem, the knowledge of particle physics would be very important to find out the dark matter abundance, its cross section with nuclei in direct detection experiments, the cross section for producing gamma rays or other stuff which we treat as indirect evidence of dark matter etc. One of my colleague here (who specializes in UV astronomy, high energy astrophysics) gave a follow up seminar bringing up an astrophysics problem which could be linked to dark matter in some ways which I do not understand yet. It's about the Missing Baryon problem. This is about the fraction of baryons predicted by big bang nucleosynthesis (BBN) which remain unobserved (about 30% if I am not wrong). Initially I thought this is similar to the Missing Satellite problem which is generic in cold dark matter scenarios which predict more number of satellite galaxies in the clusters which are not observed. Missing Satellite problem can be fixed in scenarios of warm dark matter or non-thermal production of dark matter scenarios well studied in the literature. But this missing baryon problem seems to be different as my colleague says. Its independent of cold or warm dark matter scenarios. Its hard to understand from theory point of view, where those baryons could have gone. Certainly they cant decay into something else, may be BBN scenario has to be modified, but that's also tricky as BBN is one of the very successful predictions of big bang cosmology. I got a Nature news today ( which talks about a paper claiming that the missing baryons have been spotted in the X-ray data. If confirmed, it would imply that the missing baryons are not exactly missing but just were not being detected somehow. Anyways, it might be too early to settle this mystery and more future data analysis like this group would be needed.