A serious misunderstanding..........:(

I had a serious misunderstanding in my knowledge of CP violation in the standard model sector as you might have noticed from my previous posts. What I was thinking is before electroweak symmetry breaking(EWSB) takes place there is no CP violations in the standard model sector. I thought since the standard model particles do not acquire any mass before EWSB hence there is no difference between mass eigenstates and flavour eigenstates. Hence there is no mixings in quark as well as leptonic sector.
I was attending a talk by Rajasekaran from IMSc, Chennai in the NuGoa'09 Conference (http://www.icts.res.in/program/AspectsOfNeutrinos) where he talked about the unification of quark mixing and neutrino mixings at high energy. I raised the doubt what is the meaning of mixings at very high energy say at the GUT scale. Then Prof Uma Sankar and Prof C S Aulakh pointed out that the mixing means mixing between Yukawa's , not between masses. So it does not matter whether EWSB takes place or not, the mixing is always there. Thanks to NuGoa conference, I could clear this major doubt among many others which I will write shortly.

SERC Main School in THEP, 2009

Last week I came back from the SERC main school which was in IIT Guwahati. It was a very tiring train journey which was pretty obvious looking at the distance between Ahmedabad and Guwahati. But the school was really enjoyable. The following courses were taught in the School

1. Introduction to String theory by Sunil Mukhi
2. RHIC & LHC by Rajeev Bhalerao
3. Extra Dimension Physics by Prashanta Tripathy & Dileep Jatkar
4. Cosmology and Particle Physics by Subhendra Mohanty

The first course was truly amazing as you may have already guessed. It was like a dream come true after attending the lectures by Sunil Mukhi. He is also a part of blogosphere. You can have a look at his blog "Tantu-Jaal"(http://sunilmukhi.blogspot.com/). He started with very basic bosonic strings on the world-sheet and to every one's surprise could also reach AdS-CFT correspondence in his 8th lecture. Although he could not do much of compactification stuffs yet the course was really fruitfull for the non-experts in string theory like me. I at least got a decent feeling of what string theory is all about. The tutor was also awesome. He was Nemani Suryanarayana and did his PhD under Sunil. Both of them kept the classroom really vibrant and active.
The course on RHIC and LHC which I thought wud be the most boring wass surprisingly proved very fruitful as well as interesting. All the credit goes to Rajeev Bhalerao of course. He is one of the coolest prof I have ever seen. He covered a great detail of quark gluon plasma in his course. I really liked the contents.
The extra dimension course was partly good. I really liked the part taught by Dileep Jatkar. He is really cool. He was supposed the be the tutor there. But Gautam Bhattacharya could not come due to cancellation of his flight and Dileel on the spot prepared lectures for the remaining half of the course. That was really remarkable. Since he is a string theorist, he changed the course title from "Extra Dimension Physics" to "Flux Compactification" ...:P
The Cosmology and Particle Physics course was OK type. I got to know some informative things rather than learning something. The teacher was in a hurry to cover many things in just nine lectures and hence missed out many important and crucial steps in between. But I liked the tutor Kaushik Bhattacharya from IIT Kanpur. Whatever he did in the class, he made sure that nobody is losing track of what is goin on in the class. I liked the Baryogenesis part of that course, the sphaleron processes etc.
The non-academic part of my stay in Guwahati during the school was even more interesting. I used to take advantage of the bus services provided by the IIT Guwahati to the city everyday after the classes. I used to go to the city to visit my friends as well as relatives almost everyday and come back in the morning next day before the class starts. Although I could not visit my native place which is about 160 km away from the coty due to lack of time yet the stay in my relative's as well as friend's place was enjoyable.
After all going to SERC school is always fun. We make new friends, see some new places and most importantly learn some good stuffs. I would definitely be looking forward to the next SERC school which I hope will be in a nice place as well as will have some interesting courses.

CP violations in Standard Model

In my previous post I wrote about my confusions regarding the contribution of CP violations present in the standard model to leptogenesis/baryogenesis. I have now got it cleared now. Basically the Shakarov's conditions talk about the violation of total baryon number, not generation wise violation which is intrinsic in the standard model also because of CP violation. Before electroweak symmetry breaking there was no CP violations in the Standard Model since the mass eigenstates and the flavour eigenstates were identical. But for Baryogenesis to occur we must have total baryon number violating processes at high energies which are of course suppressed at low energies.

CP violation

While reading some stuffs related to neutrino oscillations, I realized that neutrino oscillations can happen only after Electroweak Symmetry Breaking (EWSB). Since before EWSB happens, neutrinos( in fact all leptons and quarks) are massless and hence there is no oscillation and thus there is no CP violations. I started wondering about the cosmological significance of the CP violation in the leptonic sector. According to Shakarov's criteria CP violation is a must for leptogenesis to start. Now if the CP violation we see in the leptonic sector has something to contribute to leptogenesis then EWSB must happen before leptogenesis started. But according to current understanding of the thermal history of the Universe the matter-antimatter asymmetry started long before the Gev scale (EWSB). Thus whatever CP violation is there in the leptonic sector has no contribution to the leptogenesis. Although I have very little knowledge in leptogenesis, I found this point interesting. I asked my supervisor regarding other sources of CP violations which can contribute to leptogenesis. Then he said right handed heavy neutrinos is one such source. I have seen many models with B-L extended gauge symmetries which can accomodate right handed neutrinos. Now there are certain things which are not clear to me:
1. Why right handed neutrinos should preferentially decay to leptons rather than anti-leptons. I want to know how the CP violations take place in this case. Its definitely not like the oscillation of leptons which gives rise to CP violation in the usual leptonic sector.
2. Is it true that total lepton number is violated in such decay of right handed neutrinos? If yes then how can we incorporate these lepton number violating interactions in B-L extended gauge models where B-L breaking scale is not as high as the scale of leptogenesis.
I think I need to do some more careful studies rather than blindly coming into any conclusions. If anyone can help me with some references or comments that will be highly applauded.

Mt Abu trip

After around two months my stay in Ahmedabad, India I could go outside the city for a small trip. Life in Ahmedabad is like in a prison for me since I have to be in the institute from 9 am(breakfast time) to 9 pm(dinner time). Anyway thanks to Dr Ramesh K Singh (Professor in ME, IITB) who made our dream trip a reality. Believe me if you are planning to go for some trip please include him in your team. He is such an enthusiastic and energetic person that he can make anything happen. Anyway, we went to Mt Abu, Rajasthan. We were six together in the trip; me, Brijesh, Ramesh, Vishnu(Professor in IEOR, IITB), Subrata( Lecturer in Chemistry,IITGN), Abhijeet(lecturer in Economics, IITGN). We started from Ahmedabad on 21st Feb(Saturday) and reached Mt Abu at around 2 pm on the same day. We hanged around the town that day and in the evening went to the sunset point. I had lots of junk foods there which fortunately didn't make me sick.
The next day morning we went for trekking which was the most interesting part of our trip. We chose the so called "Tiger Path" for trekking. Thank God we did not see any tiger there!!! According to the local people there, that wild-life sanctuary has some bears, tigers also. It was an 8 km long trek and was really awesome. I did not even feel tired. We went to some tourist spots after that (e.g. Guru Shikhar, Dilwara temple etc) and came back to Ahmedabad. We reached around 8 pm. It was an awesome trip. Ramesh was really amazing. Now we are planning a trip to Leh in May-June with Ramesh and Co. I hope he will make it happen once again. Leh is like heaven on earth...if this trip happens my dream of going to Kashmir will come true..

Neutrinos: Yesterday, Today and Tomorrow

Recently I went to Physical Research Laboratory Ahmedabad, India to attend a colloquium titled "Neutrinos: Yesterday, Today and Tomorrow" by Sandip Pakvasa, University of Hawaii. The talk was really interesting. He presented almost everything within that one hour talk. The best thing was he talked about both experiments as well as theories regarding neutrinos. I was totally pissed off with the neutrino physics when my friend Sushant (working in neutrino physics) used to tell me the kinds of stuffs he was doing. Almost eighty percent of his work was some coding only without any touch of physics. According to him the people who work in neutrino oscillations phenomenology keep playing with the parameters involved and try to fit the models with observed data from neutrino experiments like SuperkamiokaNDE, kamLAND etc. But after Pakvasa's talk suddenly the neutrinos have become interesting to me again.
Sandip was talking about some constraints on neutrino magnetic moments. I have got confused at some point. What I want to know is can we measure neutrino magnetic moment? And if neutrino is a Majorana fermion how can it have magnetic moment? If we can measure neutrino magnetic moment can we safely rule out the possibility of neutrino being a majorana fermion? If neutrino is not a Majorana fermion it can not be its own anti-particle which means neutrinoless double beta decay experiments are not going to give any positive results. I do not know how profound these questions are but I would need to do some careful study to clear these doubts.
I was surprised when I was going through one of Bilenky's paper on neutrino where he talked about neutrino oscillations. He said that neutrino oscillations can not say anything about the neutrino nature that is, whether its a Dirac or Majorana fermion. It is because of the fact that the expression for probability of oscillation is same for Dirac as well as Majorana fermions. So oscillation data can not say anythng about the nature of neutrino. It can only give the mass squared differences of the neutrinos.
I welcome your comments regarding my confusions or anythng you like.

11-26 Mumbai...

Mumbai..the commercial hub of India is targeted once again. In India terrorist attacks have become a part of daily life for the civilians. They face it one day..forget the other day. I dont even feel like posting these never-ending tragedy in India. We witness such events at least once in a month. Its hardly one month after the blast in Guwahati which took around 90 lives, yesterday it happened again. As alwys been a soft target for terrorist Mumbai became a victim once again. But this time they attacked with a new and never seen strategy. It was not just blasts as happened before , there were indiscriminate firing in public places like railway stations, hospitals, hotels etc which finally lead to a hostage situation. They captured hundreds of people (some of them are foreign nationals) in hotel Taj, Oberoi Trident and in Nariman House, made them hostages. Sources say they were looking for specifically US and UK citizens. Although the situation seems under control now after 24 hours of gunbattle,panic across several places I hope the lessons learnt wont be forgotten. I wont start a blame game here but the way the terrorists entered Mumbai yesterday( through the coastal areas, they reportedly came by a boat loaded with weapons) was similar to the situation in 1993 when Mumbai( then Bombay) was shattered with serial blasts. May the souls of those killed (125 so far) rest in peace and those who were injured get well soon. I am hopeful of full fledged normalcy by tomorrow across Mumbai...