Thursday, June 18, 2009

The day has come finally....:)

The day which I was looking for has finally arrived today. I will leave this place, I mean IIT Gandhinagar and go back to IIT Bombay, my loving home institute. I was having a real hard time here due to extremely hot weather, no mess facilities for food for the last two months. I fell sick many times for those outside food. Anyway I am happy that I am going back. Hope my guide will also come back soon to IITB.

Monday, June 15, 2009

The Darker Black Hole...

Black holes as we know are the infinitely dense objects in the Universe which keeps sucking the matter around it. They are generally formed from the gravitational collapse of stars . They are dark in the sense that even light can't escape their gravitational field. But from quantum mechanical point of view they are not so dark as they keep radiating( so called Hawking Radiation). So far the observed black holes are formed from the collapse of ordinary matter we see around us. However its worth investigating the possibility of a black hole which cud have formed from the collapse of dark matter: the darker black hole so to say. I had a few words with Dr. Yajnik regarding this couple of days back. He was saying the number of such darker black holes may be very much constrained from the structure formation data. Since dark matter particles will decouple very early (compared to usual standard model particles) and hence will start forming potential wells....and finally collapsing on its own. If such formation takes a long time like billion years from the big bang then it won't be constrained from structure formation data. But early formation will be tightly constrained.
I am just wondering how such black holes can be formed. One obvious thought comes to mind which says it may be formed from the collapse of a dark star. But does such dark star exist? Very difficult to predict. I found a paper( by two fellows from SUNY, Buffalo where they assume neutralino as dark matter particle and show that neutralino star can't exist. I have no idea how reliable their calculation is but it sounds really interesting. So is there any other way by which such darker black holes can form? If yes how and how tightly it will be constrained from cosmology observations?
After few day I saw a news which indeed talked about such stuffs. According to some physicist in University College London very highly massive black holes can be formed from collapse of dark matter. They call it "Dark Gulping". Only future observations will tell how much truth is there in their model. But the topic is really interesting. In fact although in the above mentioned paper people have shown that dark stars can't exist, they are assuming that the dark matter particles only have weak interaction. But it may well be true and worth exploring that there is a dark sector where the dark matter particles may have strong self-interaction which can arise from some hidden sector gauge group. People have worked on such dark sector models but I have not found any paper where they talk about star or black hole formation from dark particles. I am really excited about this new field and would be looking forward to work on it as well...:)

Tuesday, June 9, 2009

Finally got rid of sneutrino vev...:)

Finally I could get a vacuum in our model with no sneutrino(super-partner of the neutrino) vev(vacuum expectation value). That is quite relaxing for me since R-parity will be preserved now in the model. I have seen many models where people work with sneutrino vev also, but somehow I don't prefer that kind of scenario. The main problem in that case would be the stability of the dark matter candidates. In our model however one sparticle gets a vev. It is the superpartner of a sterile neutrino which we have added as a gauge singlet with zero B-L charge. I think even if it gets vev, R-parity won't be violated since it has zero B-L charge and R-parity is defined as $R_P =(-1)^{3(B-L)+2s}$, where s is the spin of the particle. I hope the remaining things will be pretty simple after getting the vacuum solution..........:)

Sunday, June 7, 2009


I was in PRL (Physical Research Laboratory), Ahmedabad last two days. It was really fun (not from research point of view by the way..:P). After so many lonely days in Gandhinagar, I found myself among so many PhD students there. The crowd was really cool. I stayed in the hostel there with one of my friend. It was ten minutes walk from PRL. The best part was cricket. They play cricket every evening(during weekend). They have a small concrete court (which was basically made for basketball) with six halogen lights (good enough to illuminate it). I played cricket after a long long time. Although it was real fun, the whole body is paining now...:(. I came back today although people there insisted to stay back for today's cricket. Hopefully will visit PRL again..(may not be for research purpose but surely for cricket)...

Friday, June 5, 2009

My recent visit to CTP

While I was in New Delhi last week, I got a chance to visit CTP (Centre for Theoretical Physics), Jamia Millia Islamia ( It was an unofficial visit however. I mailed Dr. Rathin Adhikari there before I left for Delhi and he happily agreed to have some chat with me to discuss about the recent model worked out by him and other co-authors including Ernest Ma. It was a pleasant weather. I reached there at noon. The campus as well as the surrounding place was fantastic. It is very close to New Friend's Colony which is supposed to be a very posh area in South Delhi. Specially the facilities research scholars get there is mind-blowing (well that may be because we here in IIT Bombay get absolutely nothing in terms of such facilities). There the students have their own individual cabin with computers, internet, book-shelves etc etc. I wish my home institute made such effort to provide some facilities. Anyway my meeting with Dr. Adhikari was very nice. We talked about the prospects of dark matter in his model in the context of positron excess data observed by PAMELA, ATIC etc. He asked me to come next day also but unfortunately I had other plans and I told him I would keep communicating through mails regarding any progress in this work. Link

Thursday, June 4, 2009

JaxoDraw Rocks!!

It has always been a problem for me to draw feynman diagrams until today. Today I came to know about JaxoDraw( is similar to axodraw but has graphical user interface. It has become so trivial now, we can just draw it, export it in an eps format and just put it in the Latex file we are making. It truly rocks!! more feynman diagram nightmares....:)..:P